Turbo / Boost Problem Troubleshooting

Last updated: February 23, 2003

From: dvandit@istar.ca
(by way of Tom Jelly (thanks Tom)

Derek Vanditmars has a must-read site on this. Go here for the original - I just saved this in case something happens to it.

Troubleshooting Sequential Turbocharger problems:

Most of the problems with the Turbochargers is not the Turbochargers themselves, but the Control System for the Turbochargers. Prior to attempting any Turbocharger troubleshooting get a boost gauge and install it. The boost gauge is your primary instument to monitor the general health of your turbochargers. It is also highly recommended that you get the boost gauge BEFORE you have any problems so you will be able to notice what is different. The most common problem is air lines popping off solenoids or actuators that are supplied from the Pressure Tank or directly from the Primary Turbocharger compressor. So don't sweat it when the turbochargers suddenly don't work, as it is most likely something to do with the Control System. It is recommended that you follow the order of items below when troubleshooting problems.

Primary Turbocharger

You first need to get the Primary Turbocharger working before attempting to fix anything on the Secondary Turbocharger. The Secondary Turbocharger requires the Primary Turbocharger to generate more than 8 psi to operate actuators that control the Secondary Turbocharger.

Primary Turbocharger Leaks

In order for the Primary Turbocharger to operate and generate more than 8 psi check the items indicated on the Primary Turbocharger Leak Diagram. The items below are on the diagram and are listed in most likely to fail order:

  1. Y-Pipe connector hose, (coupling):

    This is a very common failure part. This short hose, (coupling) will split and vent boosted air in copious amounts. The trick with this one is that when just looking at the part on the car it will look just fine. You need to remove the 90 degree plastic duct on top and examine the rubber coupling by gently stretching it to see if there are any splits. Typically costs about U$47 at dealer.

  2. Check ~1" dia hoses for leakage:

    If you can rotate these hoses while attached, then the clamps are too loose. Get properly sized screw-clamps if the stock ones are not up to the job. New hoses will also help, but usually tightening the hose clamps is enough. A sign that there is air leakage is the presence of oily dirt on the aluminum casting around the hoses. New hose-clamps will set you back about U$10 maximum for good ones.

  3. Primary Turbo Inlet:

    Typically collapses under high volume air through air cleaner into Primary Turbocharger. When the engine is cold the rubber is less prone to collapsing. Typical symptoms are having boost at lower RPMs and then a loss of boost at higher RPMs, this is agravated when engine warms-up softening the rubber allowing for easier and more complete colaspe of the hose. Typically costs about U$90 at dealer.

  4. To/From Intercooler:

    Same symptoms as the Y-Pipe coupler. When under boost, the hose-clamps prevent the hose from expanding due to the air pressure inside the hose. Do not under-estimate the force of 10 psi or more on 3" diameter hoses, what looks OK with engine not tunning may not work under boost conditions.

  5. Air Bypass Valve:

    Test for leakage and operation. At 14-22 kPa {100-170 mmHg, 3.9-6.7 inHg} of vacuum to the control port air will flow through the two larger ports. At 31.3 kPa {235 mmHg, 9.2 inHg} of vacuum to the control port the valve will be fully open. Note that the operating points of the Air Bypass Valve are different from the Charge Relief Valve. The Air Bypass Valve is essentially the factory blow-off valve. It isn't computer controlled, but simply operates by the vacuum within the Intake Extension Manifold, (pressure = closed, vacuum = open). You will hear the Air Bypass Valve vent boost when you let off the gas and get a vacuum in the Intake Extension Manifold. Typically costs about U$150 at dealer.

  6. Charge Control Actuator:

    When closed, this prevents Primary boost from going into the Secondary Turbocharger. This valve seals the air passage the same way as the throttle butterfly valves. This remains closed until 4,500 RPM AND Secondary boost pressure is the same or more than Primary boost pressure.

Primary Turbocharger Control

Wastegate Solenoid / Actuator

The Wastegate allows exhaust to be bypassed around the turbocharger to allow control of boost pressure. Once boost pressure reaches a set value, (ie 10 psi) then the wastegate opens to slow down the turbocharger.

Secondary Turbocharger

You first need to get the Primary Turbocharger working before attempting to fix anything on the Secondary Turbocharger. The Secondary Turbocharger requires the Primary Turbocharger to generate more than 8 psi to operate actuators that control the Secondary Turbocharger.

Secondary Turbocharger Leaks

Assuming you have checked and verified the Primary Turbocharger for leaks there are several leakage paths specific to when the Primary and Secondary Turbochargers are operating, see the Secondary Turbocharger Leak Diagram. The item(s) below are on the diagram and are listed in most likely to fail order:

  1. Charge Relief Solenoid / Valve:

    Test for leakage and operation. At approximately 22.7-30.7 kPa {165-235 mmHg, 6.5-9.3 inHg} of vacuum to the control port air will flow through the two larger ports. Note that the operating points of the Charge Relief Valve are different from the Air Bypass Valve. The Charge Relief Valve vents boost during the pre-spin stage of the Secondary Turbocharger, (3,000 to 4,500 RPM). The Charge Control Valve isolates the Primary Turbocharger boost from the Secondary Turbocharger during the pre-spin stage. After 4,500 RPM the Charge Relief Valve is closed to allow Secondary boost to be added to Primary boost.

Secondary Turbocharger Control

At this time you should haved the Primary Turbocharger functions completely, and checked the Secondary Turbocharger for leaks.

  1. Turbo Control Solenoid / Actuator

    The Turbo Control Solenoid / Actuator is one of the more complicated actuators as it requires vacuum and pressure to operate properly.


The normal boost pattern and method of testing is as follows:

  1. Steps should be done in order. Failure of any step will require further inspection prior to continuing.

    WOT = wide open throttle

    KOKO = Key On Key Off

  2. Verify engine is at operating temperature.

    Remove Double Throttle Actuator vacuum line

    At operating temperature, no vacuum should be present with engine idling.

    Re-attach hose

  3. Check engine vacuum at idle

    Vacuum reading should be above 15" with Air Conditioner OFF, typically 17" to 19"

  4. Check no-load operation of Primary Turbocharger

    Briefly accelerate engine to WOT in neutral, +4 psi should be obtained.

    If you do not get this you most likely have a leak of the boosted air. This is anywhere from the turbos to the intake manifold. See Turbo Leak Diagram for helpful hints.

    If get +4 psi, then watch the Turbo Pre-Control Actuator rod for movement

  5. Check vacuum chamber's storage ability with engine off

    Pull off vacuum hose at Charge Relief Actuator

    Should hear air entering hose vacuum, re-attach hose

    Start engine - briefly accelerate engine to WOT in neutral again

    Turn engine off - KOKO 6 TIMES

    Watch Charge Control Actuator work each time

    Watch Turbo Control Actuator work each time, (need to crawl under the car to see this one)

  6. Check Pressure Tank's pressure storage ability with engine off

    Pull off one of the hoses of Pressure Tank

    Should hear air leaving tank (pressure), re-attach hose.

  7. Road test with boost gauge

    Drive to third gear with normal acceleration

    Accelerate from 35 MPH at WOT until passing 4,500 RPM

    A slight and smooth increase in power should be felt at approximately 4,500 RPM. This will be about 65 MPH.

    RPM		PSI	
    3,000		10	
    4,500		8 as secondary turbo comes on	
    4,500 +		10 recovers almost immediately	
    6,000 +		8 and holds to redline	

    These readings indicate normal operation. Readings will vary with altitude and temperature, (i.e. lower temperature = higher boost).


The Control System for the Turbochargers is composed of the following:

  1. Input

  2. Control

  3. Output (Air Supply)

The Air Supply column indicates where the solenoid and actuator gets its air supply from.

Vacuum is supplied from the vacuum chamber, this chamber is supplied with a vacuum from the intake manifold via a one-way valve. The one-way valve allows the vacuum chamber to keep a vacuum while the intake becomes pressurized from the Turbochargers during boost.

Primary is supplied directly from the Primary Turbocharger compressor. Note that the primary turbo must be operating and generating more than 7 psi of boost to be useful for any of the solenoids or actuators.

Pressure is supplied from the pressure tank, this tank is supplied with pressure from the primary turbo's compressor via a one-way valve. The one-way valve allows the pressure tank to keep a pressure while the primary turbo is not producing boost. Note that the pressure tank requires the primary turbo to be operating and generating more than 7 psi of boost to be useful for any of the solenoids or actuators. It is VERY common for either one of the hoses to the pressure tank to pop off due to pressures greater than 12 psi that the tank holds due to boost spikes and the hoses becoming old.


Q: I have oil in the air intake piping or intercooler ducts

A: During boost, the PCV valve closes and any engine blow-by is directed through the air intake ducts near the Primary Turbo Compressor. This results on "some" oil to deposit over time in these areas. This is normal, assuming there is not excessive oil burning coming from the exhaust.

When intake manifold pressure below atmosphere pressure, the blowby gas flows through passage 1 and is pulled into the intake manifold. When mainfold pressure at or above atmosphere pressure, the PCV valve closes and blowby gas flows through passage 2 and is pulled into the intake portion of the Primary Turbocharger.


Rebuilding and/or replacing the Turbochargers

OK, you have found out that the Turbochargers do actually need to be replaced, (major bummer). I read somewhere that anyone with a turbocharged car should really look at the turbocharger as a "consumable" part, much like clutch, brakes, etc... this may make you feel better but will not help with the cash-flow situation.

If you do not know of a good Turbocharger re-builder, then look in your local Yellow Pages directory under, hey you guessed it "Turbochargers". Phone everyone listed and ask them if they have worked on your type of Turbocharger for the 3rd Gen RX-7. There are basically two types of turbocharger re-builders, one will just work on the turbo cartridge and you get to remove this from the RX-7 specific exhaust and compressor housings. The other type of re-builder will accept the whole RX-7 turbocharger assembly. Both have their advantages and disadvantages.

Turbocharger cartridge rebuilders will cost you less for the re-build of the turbos, but you will need some special tools to remove the housings and some set-up jigs to have everything re-align when putting everything back together. The other thing is that typically there will be cracks in the cast iron exhaust housings, typically around the wastegate, where the exhaust enters the housing from the engine, and around the exhaust wheel of each turbo. These cracks can be anywhere from benine to irreparable depending on how deep and where they are located. Any cracks that are where the exhaust wheel is is generally considered irrepairable. For around the wastegate these can be welded up or some shops can machine and put an insert in. Note that any of this type of welding must be performed at a shop that does this kind of work, see Turbocharger assembly re-builders. So in the end, you may spend about the same amount of money, except that it will not be all in the same place. Another disadvantage, is that re-assembling the turbocharger into the RX-7 housings requires lining up oil in/out fittings and compressor outlets with respect to the exhaust manifold attachement plane, non-trivial and requires measuring or adding alignment marks of the various parts prior to disassembly.

Turbocharger assembly re-builders will cost you more but you get the complete assembly under warrenty. It is very important that the place you use has experience with the 3rd Gen RX-7 turbochargers, because there are a bunch of non-obvious things that a first time rebuilder will not realize about re-assembly of the turbos and the housings as mentioned in ther previous paragraph, (ie alignment of oil in/out fittings and alignment of primary and secondary compressor outputs).

For questions or feedback mailto://dvandit@istar.ca

(Editor's note: See my page on Turbo Rebuild from more info on rebuilding, where to get it done, etc. --Steve)

Date: Sat, 16 May 1998 19:22:16 -0500
From: David Liberman

>I'm in the home stretch. I've replaced the following components to solve
>my secondary turbo problems (no boost from second turbo after car is warm).
>1. New turbos
>2. New control solenoids
>3. New engine (related to oil leak)
>4. New MAP sensor
>5. Wire-tied hoses
>The performance has increased significantly since last year, but there is
>After the car is warm, accelerating past 4500 rpm produces no secondary
>boost all the way to redline, however, if I shift to the next gear, the
>second turbo comes on line in that gear.

Sounds like a problem related to the ECU. The computer could be bad, there could be a wiring or sensor problem, etc.

Try this test. When the problem occurs, put the car in neutral, and cycle the key off and back on, starting the car. This will reset the ECU. Accelerate, and see if you still have the problem. If not, I'd get your ECU replaced and try again. It's an easy swap.

If the ECU checks out okay, then I suggest starting at the other end, with the sensors that supply the ECU with its data. If you don't already have a Mazda shop manual, this would be a good time to get one.

Date: Sat, 11 Jul 1998 16:24:17 -0700 (PDT)
From: kiredjia


My car had been consistently producing low boost since I purchased it with 47 k miles on it. I saw 7psi on the primary turbo, and between 5-7psi on the second. Examination of the intercooler piping revealed no boost leaks, and no loose vaccum hoses were found.


It turns out, the previous owner replaced the vaccum hoses leading to the the turbo precontrol and wastegate actuators without reinstalling the restrictor pills usually found it them. He most likely was running an electronic boost controller on the wastegate actuator hose, and replaced both lines when he removed it to sell the car (both hoses were new rubber with zip-ties, unlike other hoses on the car). He probably neglected to realize these lines required restrictor pills.

As I understand it, not having the restrictor pills allowed the actuators to see higher pressure than they should have. This caused them to function prematurely. Opening the precontrol early bled off exhaust gas from the primary turbo to the secondary, thus reducing boost ( and giving me a very smooth transition from primary to secondary). The wastegate was also opened prematurely, preventing me from building full boost even on the secondary turbo.


I chose to install bleed valves in both lines instead of pills, allowing me to adjust the amount of restriction. The valves were mounted in the engine compartment, next to the passenger side relays. In this location, using approximatley 2.5 feet of 7/32 vaccum line for connections, I needed to close the valves until they were approximately 1/2 turn from fully closed. I am still not certain about the turbo precontrol seeting, but I am now getting 10-12psi with spikes to 14 (a little high?).

For those with low boost problems, this is a relatively easy cause to investigate. Both hoses are readily visible with the intake removed. They are easily pulled and replaced (although the turbo precontrol hose was easier to install from underneath the car). I have not seen what the pills look like, but the hoses are short enough that it is very easy to see if there is anything in them. Thanks again to everyone who helped. If anyone thinks they have the same problem, let me know and Id be glad to help. Its a shame to see such a wonderful car brought down by a $0.05 piece of plastic!

Date: Thu, 30 Jul 1998 19:49:51 -0700
From: Dana Bourgeois

You know how there is a pressure tank and a vacuum tank in the turbo control system? The vacuum tank is connected to the manifold via a one-way valve. At idle, the manifold evacuates the vacuum system through this valve. Under boost, the valve closes keeping pressure to no more than 1 ATM.

The system uses boost pressure to power the actuator that opens (and holds open) the gate bringing the second turbo online. One side of this actuator is connected to the pressure system and one side is connected to vacuum. Normal operation is that the vacuum system never gets pressurized so worst case, the second turbine is kept on-line by pressure on one side and atmosphere on the other. A leaking one-way valve results in pressure on one side and a slow build up of pressure on the other side of that actuator so the second turbo transitions OK but can't stay on-line.

My original one way valve passed the classic 'blow both ways' test. But removing it to test it a third time, the nipple broke off. The replacement valve kept the second turbo alive.

I think a pressure switch/idiot light on the vacuum tank would be a good idea since it is so easy for that cheap little valve to leak. Anybody know the cost/PN for an automotive pressure switch?

Date: Sat, 5 Sep 1998 11:41:28 -0500
From: "Steve Wynveen"

Yeehaa, my car is finally 100%, probably for the first time since I bought in April '97. I also fixed my problem with always having low boost on the second turbo in 1st gear only. The problem was with the solenoid valve that controls the vacuum signal to the turbo control actuator (TCA). It turns out the bad solenoid was going open circuit when it got hot (from engine heat). This somewhat intermittent nature made it a true pain to diagnose. Luckily, the problem was getting worse this year & the low boost was cropping up more consistently. I now see 10 psi on the second turbo in 1st gear all the time...what a difference in acceleration!

I must also thank Peter Farrell for giving me some advice over the phone on the order to carry out my troubleshooting. Here is what I did, and the equipment used:

My already had a boost gauge in my car (installed late last summer). In addition, I purchased a vacuum/ pressure test gauge from Sears for $20, and already owned a vacuum hand pump with gauge (Mity Vac), a pressure hand pump with gauge (sold in personal watercraft catalogs - used for testing pop-off pressure on diaphragm carburetors), and a good multi meter. The low boost on the second turbo made the TCA suspect, in that it wasn't getting either the pressure or vacuum signal, both of which it needs to work correctly. Here is the test procedure:

1. Tee into the side fitting on the TCA, right next to the TCA. This is the pressure port. Go out and warm up the car thoroughly. Accelerate from 2k rpm at WOT in 2nd gear to well past the turbo transition point at 4500 rpm. Before the transition, the test gauge should read atmospheric (0 psi, actually 0 psig, but I won't get into the nomenclature). At the transition, the gauge should IMMEDIATELY jump to pressure (>7 psi ?) and hold as long as you have the gas mashed (don't hit the rev limiter, please). If you don't see the jump to pressure, this tells you that something in the pressure side of the control system is awry. I had pressure, so I didn't go down this road.

2. Tee into the fitting in the center of the actuator, the one that points toward the front of the car. I pulled off my plastic under tray for better access to the actuator (you don't want to drive you car for very long or had without the tray. I have heard of people overheating their cars without it). Again, tee into the line and go for a drive. With the car fully warmed, do the WOT test in 2nd gear from 2k rpm again. This time, you should see the gauge jump to vacuum at the transition, and hold. I saw no vacuum. In fact I saw a very quick jump to ~1/2 psi pressure, which immediately fell back to 0 psi. This is just because, on my car, the pressure side of the system was still enough to drive the TCA, only slower than intended. When the pressure pushes the diaphragm down inside the TCA, the vacuum side of the TCA reduces in volume, causing the quick, slight pressure spike.

3. So, we know I am getting no vacuum to the TCA. This means either that the turbo control solenoid valve has failed, the vacuum check valve has failed, a vacuum hose has popped off, or one of the other two solenoid valves in this vacuum system is stuck open, venting to atmosphere. The easiest to check was the check valve. I pulled out the appropriate check valve and applied 12 psi to it from the manifold side, to simulate running under boost conditions. The valve didn't leak, and shaking it around didn't make it leak either. Next, I drew vacuum through it, and it let vacuum flow in the proper direction. So, the check valve is eliminated. Next, plug my Mity Vac into the line coming off the check valve and pump the system up to ~ 15 inHg vacuum (a fair amount of pumping). The system held vacuum, indicating no major leaks when all solenoid valves are de-energized and no cracks in the vacuum reservoir.

4. Road test. Tee into the vacuum system either just PAST the check valve, or by the entrance to the vacuum reservoir. Go for a drive and do the WOT test from 2k rpm in 2nd gear again. You should see vacuum all the time, and a drop in vacuum as it gets used at the turbo transition point. When driving gently, the system should hold a high, steady vacuum. In not, something else in the system is wrong, possibly a solenoid valve. If, at the transition, the system drops to zero, or something very low, a vacuum line popped off somewhere is indicated. In my case, everything looked like it should, high stead vacuum (~20 inHg) with a slight drop at the transition (to ~15 inHg).

5. All indications at this point were to the turbo solenoid valve that runs vacuum. This is the one bolted to the secondary air control valve assembly. It is the valve NOT in the big rack of valves by the spider. On my under hood diagram (1994 car) it is item #12. At this point it must either be a bad solenoid valve, a blockage or pinched off line before or after the valve, or electrical. There's only one way to check this, pull off the extension manifold (yipee!). So, about 1.5 hours later I'm down to the solenoid valve. (By the way, I'd highly recommend gently stuffing some paper towels or rags in the 4 passages exposed on the lower manifold. It is just WAAAY to easy to drop something down there accidentally - like puke, sorry Isaac I couldn't resist -, and then you really have big problems.

First, I checked the valve by applying battery voltage across it by using jumper wires. The top terminal is +, and the bottom is ground. Peter Farrell told me that clicking is not enough to indicate a good valve. Sometimes they click, but the plunger is broken internally. So, I first used my Mity Vac to put the vacuum system into ~ 15 inHg vacuum (same place as used before). When I applied voltage it clicked, and I could hear the actuator move. This also eliminates a blocked or kinked off line to the TCA. Damn, I thought, an electrical problem in the harness. Just what I need.

6. Check out the electrical harness. I reconnected the battery & turned on the ignition (DON'T turn over the engine - you'll suck up the towels in the manifold I recommended in step 5). This sends power to all the solenoids. The ECU runs them by grounding the other side of them. The solenoid valve had battery voltage. OK, it has to be the ground. So, I should pull out the ECU and measure continuity between the solenoid's plug (yellow/blue wire) the appropriate ECU harness terminal (#4R). However, there is an easier way. The electrical diagram shows that both turbo control solenoid valves (pressure and vacuum) are grounded by the same 1 wire at the ECU. Somewhere along the way they join together. We know the pressure solenoid valve works (saw pressure at the TCA in step #1) so its connection to the ECU must be fine. Therefore, we can just check for continuity between the ground terminals of both solenoid valves (valves #12 and #26 on the underhood diagram, ground is yellow/blue on both). I used a long skinny screwdriver as the conductor to get to the #26 valve without having to dig the valve out. I saw .2 Ohm. Damn, everything checks out, what the hell is wrong!!

7. Back to step 5. I played around with the jumper wires to the solenoid valve some more. At this point, things were still a bit warm, as I pulled the manifold off without letting the car cool for very long. All of a sudden, the valve stopped clicking. I pulled out the valve and did some more testing on a bench. It clicked again. I though to myself, maybe it is heat related. Next, I measured the resistance of the solenoid - 34 Ohm. Then, I pre-heated my oven to 175 deg F and baked the solenoid for 3 min. When I pulled it out and check continuity - open circuit. As the solenoid cooled, it began to show very high resistance and slowly came back to a realistic valve. Yipee, I though, here's the problem, a temperature sensitive valve.

8. I ordered up a new valve and manifold gaskets to get overnighted from Mazda Comp. Put the car back together, and it now works as Mazda intended.

In closing, I must thank Mr. Farrell for his guidance in getting me started. I must also say for shame to those mechanics that told me it was normal to not get full boost on the second turbo in 1st gear because it is so transient and the engine is loaded down enough. Also, as I discussed with Mr. Farrell, do you think any Mazda mechanic would have taken the time and effort to do the diagnosis like I did? It is much easier to guess a part is bad and replace it (making money on the part and labor to install) than it is to do a proper diagnosis. Not to mention, many mechanics don't have the proper training or understanding to be able to diagnose such a complex system.


Date: Fri, 23 Apr 1999 22:13:58 -0400
From: Max Cooper

A new check valve fixed my second turbo boost problem, too. It was the valve that connects to the pressure tank, and I replaced it with a $4 generic check valve. Problem fixed; no problem with the cheap check valve yet.

Date: Sat, 5 Sep 1998 12:02:57 -0500
From: "Steve Wynveen"

Per the request of several, I am posting the dimensions for a set of plugs I made up for finding some boost leaks. Please keep in mind that these will not allow you to locate all boost leaks, as some lines only get pressure when a solenoid valve is activated. They will, however, allow you to easily find leaks in gaskets, small cracks or tears in intercooler piping & hoses, and leaking air bypass and charge relief valves.

2 plugs are 2.37" in diameter, with about a 3" dia shoulder. The shoulder isn't necessary, but keeps you from stuffing the plug in so far that you can't get it out. The 2.37" dia section is about 0.80" long. One of the plugs is drilled and tapped for a hose barb with tapered pipe threads. Onto this barb I put a hose attached to a REGULATED source of about 5 psi air pressure. You don't want to put 100 psi into the system or you'll blow the thing apart for sure. These plugs insert into the hoses coming off the airbox, going to the turbos. You should remove the airbox to be able to do this easily.

The next plug is 0.856" diameter, with this section being about 1" long. Make a shoulder if you like. This plug is for the return line from the secondary air switching valve. In hind sight, I don't think this plug is necessary, but I don't know for sure.

If you want to test all the intercooler hoses and pipes, along with the intake manifold & throttle body gaskets, this is all you need. Hook them up and pressurize the system. It may be necessary to turn the motor a few degrees if one of the rotors has happened to stop where the intake and exhaust ports overlap.

If you don't want to pressurize the intake manifold, I also made myself a plug to stick in the hose before the plastic elbow before the throttle body. This plug is 2.734" diameter. If you test with this plug, air will leak out though the PCV system and into the intake manifold. To remedy this, I unscrewed the oil fill cap, and pulled off the PCV. Reach one finger inside & plug off the breather hole and use another finger to block off the nipple the PCV was just on.

I made mine out of plastic (nylon) bar stock at work, and it was a piece of cake. The plastic machines like butter. It allowed me to quickly locate a torn rubber coupler at the top of the y-pipe this past spring. Hope this helps someone out.

From: Jake Watkins [mailto:jwatkins@devstudio.com]
Sent: Friday, October 09, 1998 9:06

Seems to be that time of year for me! I've noticed that I'm not getting full boost on my second turbo after ~5000 RPMs. The primary turbo seems capable of going to15lbs or more (accidental 5th push while going up hill, got off the gas real quick).

When the car switches over at 4500RPM I do not get a spike, the boost drops a bit and then climbs back to 11PSI and then begins to bleed down (~6PSI @ 7.5KRPM in 3rd gear).

What is causing this? Do I have a blown host on the second turbo's side or what?


Date: Friday, 09-Oct-98 09:35 AM
From: Dana Bourgeois \ Internet: (fg@portal.com)

Classic problem caused by boost pressure in the manifold leaking through a one way valve into the vacuum system. Short term fix is to replace the 2 or 3 one-way valves. Don't trust the standard 'blow both ways' test as a leaky valve can pass this test! I think the long term fix is a separate vacuum system but haven't really done more than think about it.


Date: Fri, 09 Oct 98 13:47:16 -0500
From: "Linthicum, Sandy"

Also classic symptom of clogged precat and/or main cat


Date: Sat, 2 Jan 1999 11:40:07 -0500
From: Scot Kight

Clogged cat symptoms are lowered boost, slower to make boost, decreased fuel efficiency, power, and increased heat.

These are all VERY gradual.

I think the consensus here is just replace the thing with a downpipe and dont worry about it. I know the car passes emmissions in VA just fine. And they are pretty strict. It's probably one of the best things you can do for your car. If you have an intake or catback already on the car, you might be putting the car a bit leaner then stock. It should be OK though. With no other mods, I know of noone who has had any problems.

Date: Sun, 12 Dec 1999 03:51:40 -0500
From: Wael El-Dasher (wael.el-dasher@efini.net)

> I have been trying to diagnose the cause for my lack of boost above 4500rpm.
> I have gone through as many hoses as I can manage to find and everything
> looks good.  The hose from the charge relief valve was very loose.  I
> thought I had found my problem.  The hose looked good and I put new clamps
> on it to keep it in place and figured everything would be fine.  Upon
> testing, good primary boost (10 or 11), but once over 4500, boost drops to 2
> or 3 and there is a massive hissing sound.  I know there is a leak
> somewhere, but I just can't seem to figure out which hose it is.  This leak
> is in front of the passenger side and sounds like it is something big. I had
> almost everyone of those hoses from the intake and turbo off, but they all
> looked okay.   HELP!!!!
> Another question,  since this leak sounds so large. is it possible the large
> 2 peice hose on the intake can do that?  The stock springclamps on it seem
> ok, but do these ever leak, or are they not under too much pressure??  I am
> asking because it just sound like sooooo much air is rushing through.
> Thanks for any advice.

I am really sorry to hear that you are still having trouble with your secondary boost. I would like to point out that Rob Robinette is correct, don't expect to find a large hole. It would more likely be a hose that popped off or one with a small slit.

Since your secondary is producing a small amount of boost (2-3psi) with the primary after switchover then it is more likely a slit. But there are a few key solenoids you should look at first. Below I described what I would do to trouble shoot this problem. This e-mail assumes you already checked the Charge Control Solenoid and it's associated hoses that allow the Charge Control Actuator to open the valve for the secondary turbo to come online. I will not go through them as I already explained them to you in an earlier post. I am assuming you already checked them and followed my instructions and found no trouble.

Before I begin, if you do not have a Workshop manual or a Service Highlights Manual then get either of them first. If you do have one then follow my descriptions with the diagrams and drawings to understand the routes I described. Here goes.

First, a simple rule that I always followed is to check the hoses that are exposed, so check the 4 hoses going into both, the Wastegate Control & Turbo Precontrol Solenoids, they are the 2 attached to the front of the upper intake manifold and are paired together (sort of army green colored). If the hoses are fine then I assume it is something related to the secondary coming online.

During high speed/high load conditions (secondary online) there are 2 solenoids that control the secondary turbo coming online:

1. Charge Relief Solenoid
2. Turbo Control Solenoid (actually there are 2 turbo control solenoids)

The Charge Relief Solenoid's function is to control the Charge Relief Valve (CRV). While the secondary is spooling vacuum travels through the hose that is attached to the top half of the CRV, after 4500rpm, at switchover, boost travels through that hose, so the CRV is closed and the secondary turbo does not bleed air while it is online.

Therefore, the Charge Relief Solenoid is what controls when vacuum or boost travel through the hose attached to the top half of the CRV. To track down any leaks you will need to look at the source of the boost that is supplied to the Charge Relief Solenoid, allow me be to explain.

Let me step back and explain a very simple way to understand how the solenoids direct air, I think it is important to know this as it will help you trouble shoot solenoid problems in the long run.

Solenoids recieve boost from the back (if they have a line coming in the back, if they have a filter then they recieve boost from the front), it is the metal nipple in the back near the connector. The solenoids themselves are not linear, ie they are simple on/off (I/O).

Now when air comes in the back it is allowed to exit from the front through the upward pointing nipple (plastic nipple). This is what the manual calls the OFF position. The nipple pointing forward in the front (not upwards) is always closed until the solenoid opens it, when it does open the forward pointing nipple, this is called the ON position, however in the ON position both the forward and upward nipples are open (if someone know s otherwise please advise). This is simply how the solenoids work, think of them as air management.

Back to your problem. During boost (secondary) the Charge Relief Solenoid recieves it's boost from the Charge Control Solenoid. The hose that carries the boost from the Charge Control Solenoid comes from the forward pointing nipple of the Charge Control Solenoid, which is activated after 4500rpm, ie ON after 4500rpm, but it is not used before 4500 rpm(Charge Control Solenoid OFF). So check that hose.

Next, if that hose is fine then move downstream, once the Charge Relief Solenoid is ON, boost is allowed to exit from the 2 hoses in the front, both are U shaped hoses. Check them.

If these 2 hoses are fine, then follow each downstream. I will take the upwards pointing nipple off the Charge Relief Solenoid first. We know this on has vacuum before 4500rpm, but you can't assume it has vacuum and that all is well before 4500rpm, even if it had a leak, your CRV will vent because the pressure from the secondary turbo spooling could be great enough to open the CRV without the aid of vacuum in the top half of the CRV. So check the hose going from the top half of the CRV. It goes from the CRV to a nipple on the lower intake manifold and eventually routed to the Charge Relief Solenoid. Check also the 4 vacuum lines that come out together on the other side of the lower intake manifold.

If all these are well then it is time to track the forward pointing nipple from the Charge Relief Solenoid. Check the horizontal U shaped hose, if it is OK, then it's time to follow it to the end. It goes into the metal lines, but these line take it to 2 places; the first is to the vacuum chamber behind the powersteering and A/C pulley plate (under and to the right of the alternator), and the second to the Turbo Control Solenoid (not the one next to the Charge Control Solenoid in the rack, but the other one next to the Air Control Valve on the lower intake manifold).

So check the hose going into that Vacuum Chamber, it tends to break easily if it was never replaced, expecially when you change the belts. The Vacuum Chamber is connected (not directly but through a T earlier in the metal rack lines) to the hose which carries the small Check Valve going into the front of the upper intake manifold (there is only one hose inthe front that has a small Check Valve). Check that hose, and make sure the one way valve works only in the direction pointing into the manifold. This one way valve is there to allow the boost coming out of the Charge Relief Valve (after 4500rpm) to only go into the upper intake manifold, and under 4500rpm it prevents the boost from the primary from forcing the Charge Relief Solenoid to open it's forward pointing nipple. I hope this is all making sense.

With that behind you, it's time to turn attention to the Turbo Control Solenoid (on the lower intake manifold), the lower hose going into the solenoid is the one carrying boost from the Charge Relief Solenoid, and the one on top (or closer to the manifold if you prefer) is the one going to the Turbo Control Actuator (it controls the exhaust valve port that allows the secondary turbo to come online at 4500 rpm at full song, ie after it pre-spooled). So check that hose too.

Now finally also check the 2 hoses going out of the Turbo Control Solenoid 2 (the one in the rack next to the Charge Control Valve). The one coming out of the upwards pointing nipple carries boost after 4500rpm and is meant to balance the boost from the other Turbo Control Solenoid so the Actuator will open the exhaust gate for the secondary turbo. The forward pointing nipple goes to the rack's metal lines but it is the same line that goes into the Pressure Chamber (the black box behind the alternator, it sits right on top) and the line coming from the Y-pipe with the large one way valve is meant to carry boost into the chamber (hence the name Pressure Chamber) then into the Turbo Control Solenoid 2 's front nipple (when it is ON, front nipple is open). So check that hose. BTW, that is why this solenoid has a mini-air filter on the back nipple, ie it recieves boost from the front when it is ON and it vents it from then filter.

I know this sounds complicated, but it isn't. Go over all the routes I described carefully in the manual and they will be clear, toggle between the manual, my notes and your engine bay and it will all make perfect sense.

Date: Wed, 14 Oct 1998 00:21:18 -0500
From: David Liberman

Where to start looking for the causes of boost problems:

1.  A busted hose, somewhere between the turbo outputs and the throttle body:  
        a.  the coupler at the elbow, on the pipe that goes from the turbos 
            to the i/c.
        b.  one of the other couplers in that system
2.  A busted hose, on one of the turbo accessories:  
        a.  the hose that comes out at the "Y" on the turbo outlet pipes and 
            goes to the blowoff valve will split, often times on the bottom 
            and you have to take it off or feel the bottom to find it.
        b.  the hose that comes off the secondary turbo (back of engine) and 
            feeds the charge relief valve.  Again, it can split in the darndest 

Date: Sun, 18 Oct 1998 14:47:11 -0600
From: "Derek Bentley"

The main fix to my turbo problem was a complete vacuum hose replacement. I used silicone hose, and it really sticks tight without even using clamps. There were three hoses that had come off. One was connected to the back side of the Charge Control Solenoid. The other two were the two larger hoses that connected to the elbo that is the inlet to the primary (front) turbo.

The second thing that was most likely bad was the Charge Control Actuator. This is the actuator that controls the Charge Control Valve. The pressure side nipple/fitting of this actuator was bent so that there was a pressure leak.

A third problem I found, which may have not had any effect on the turbos was the aluminum check valve (next to the PCV). It was not holding.

Date: Mon, 18 Jan 1999 15:23:53 -0600
From: "Westbrook, Chuck"

>for poor boost when in throttle when on 2nd turbo for a long time:

Maybe you have a loss of vacuum in the vacuum tank caused by a leaking one way valve. Works ok the first time because the vacuum is strong. After that you are on boost and you lose some vacuum then when you shift, the pre-control and other valves close then need to open again with less vacuum. Just an idea.

Date: Tue, 15 Dec 1998 17:14:53 -0500
From: Sandy Linthicum

> As some of you may know, I have been fighting low boost problems on my car
> for some time. I did make some real progress in returning my pattern to
> normal when I discovered (with the help of some list members) that the
> electrical harnesses on my turbo precontrol and wastegate solenoids had
> been swapped (probably during a recall). However, it seems to me that my
> boost pattern is still not completely correct -- in third gear, I see:
> 10 - 4 - 6.5.

...sounds more like a clogged precat/cat (if you still have them). Altitude affects boost pressure by making it harder for the turbo to get reach a set boost level (less air density to start with on the compression side and therefore less/slower exhaust flow as an energy source)

Usually a clogged precat doesn't bother boost level on the 1st turbo since the exhaust flow is low but by the time the second one kicks in the exhaust flow is greatly increased and the cat/precat causes massive restriction, limiting higher rpm boost, drasticly increasing EGT & trashing your engine if you keep pushing it. It can also damage the secondary turbo since it is now working against major backpressure.

You do NOT have a boost leak on the intake side if you get 10psi initially. If have a leak hear it keeps you from pressurizing the intake system period.


Date: Wed, 02 Dec 1998 14:44:12 -0500
From: David Breslau

...One way to check if you've got a restriction in your exhaust is to remove the O2 sensor from its bung, and use an appropriate fitting to replace it with a length of 1/8" to 1/4" copper tube.

Put a hose on the tube, and run it to a standard vacuum/pressure test gauge. Drive the car, and if you see more than 2-3 lbs of backpressure, you may have a clogged cat. My numbers are estimates, I haven't tried this on a known good car yet to see what baseline pressures would be. If anyone does, please post them!

Date: Sat, 9 Jan 1999 10:25:10 -0500
From: Jan Mel Poller

With 91k miles on my car, I have experienced about all the turbo hose problems that you can. Here they are:

1. There is a large diameter rubber hose the goes down just behind the radiator. Twice (maybe 3 times), I have had the hose split at the molding seam.

2. There is a large diameter hose that is invisible from above that comes out of the air filter box. There are three hoses on top, one underneath. When this one collapses (twice), you get low or no boost or vacuum (last time) when the second turbo kicks in. last time, it had collapsed into a heart shaped cross -section.

3. The small diameter hoses that go into the black plenum chamber on top of the engine: they can be cracked, disconnected or not glued on (thank you Rosenthal Mazda for charging me to replace perfectly good hoses and not connecting the replacements correctly. And, missing the cause of the problem, the hose out of the air filter. A Real thanks to Peter Farrell and Mitch Piper for finding the problem).

I also had PFS do the whole wire wrap and silicone hose job. They found several disconnected hoses.

Date: Tue, 23 Feb 1999 08:41:37 -0500
From: "John Levy"

> Is there any mechanism on the intake side (meaning not the wastgate
> control actuator) that controls or can have any effect on the boost that
> the primary turbo creates?  My boost gauge doesn't show any boost at all
> when I do the stationary WOT test (hoping to see +4 psi)  And yet I can
> get the proper 10-8-10 pattern 75% of the time (not when I have WOT). 
> 20% of the time, my car will make no more than Zero PSI if I give it WOT
> in 1st, 2nd, or 3rd gears.  5% of the time, my car will make perfect
> boost at WOT.

Often the problem is that the precontrol door is slightly adjar robbing boost from the primary before it can afford the diversion to the secondary. The solution is in properly setting the length of precontrol actuator rod. After disconnecting it from the arm of the door, hold the door closed and set the length of the rod so that one half of the arm pin is hidden by the hole in the rod end. Done properly you will have to pull on the rod in order to get the hole to go over the pin of the arm. Let me know if this solves the problem.

Date: Tue, 17 Aug 1999 21:00:46 -0500
From: "Shiv S. Pathak" (Shivp@worldnet.att.net)
Subject: Re: (rx7) [3] Part#'s for Check Valves...

Drew wrote:

> 1. The all white one:
>         N3A1-13-1995 (note: this is a revised p/n and is a very expensive
> part - $40)
> 2. The black and green one:
>         N390-13-995A ($15)
> 3. The green and white one:
>         HE41-13-995 ($15)
> Now, what is the Aluminum one. Does anybody know the p/n?

I believe it is referred to as the "PCV valve" (whether it is or not). P/N NF01-13-890. Costs $9.70 from Mazda Comp.

Date: Mon, 30 Aug 1999 17:32:04 -0400
From: Tom Walsh (TWalsh@achieversusa.com)

I have had the same problem you are describing (with a split hose leading to the I/C).

The reason I know this is not happening in Steve's case is the first number of his boost readings. 10lbs of boost. What normally happens in the case of a hose split is the opposite of what Steve has. The first turbo has a very low reading (6-7 lbs) and the second turbo has a higher reading.

Why? because if there is a tear in the connector hose, the first turbo will try to over come the leak, but because it is a small turbo it will soon run out of flow and your boost will be limited (because the turbo could not out flow the leak). When the second turbo comes on, both turbos will work together and combined they should (unless the hole is very large) be able to out flow the hole and produce a correct boost level at the manifold. So you will see a pattern in the 6-8-10 pattern... (depending on the hole size) Either way, they are both a bad situation....

It has been my experience that when both turbos have difficulty flowing (say a pattern of (5-3-5) look towards the exhaust. Something is blocking the rate of exhaust gas flow. (normally a clogged cat or pre-cat).

When you get a pattern of 10-8-6 or something along those lines, it leads me to believe there is a faulty solenoid or faulty check valve. Because you are getting good boost off the smaller turbo (which if anything were blocking the exhaust path would flow much lower.) Or try and do a visual inspection on the secondary turbo (it is easy enough to see) and make sure it is okay... And not damaged...

Date: Thu, 13 Apr 2000 18:13:00 -0400 From: "Gary C. Friedman, Psy.D." Subject: Re: (rx7) [3]Boost problem

> Ever since I had my motor rebuilt I have only been getting 5 PSI when the
> second turbo comes online.  My boost pattern looks like 10-3-5 and then 
> it will drop to 4 at redline.
> Here is what I have done.
> After trying to adjust the pre-control rod (because it was rattling) and
> snapping it I replaced it with another pre-control actuator.
> Still the same problem.
> I adjusted the new pre-control rod to get rid of the same rattle and still
> same problem.
> Got under the car looked at the actuator and it doesn't move when the car
> passes 4500 RPM.

Check the turbo harness connections (whats the right name for these list people?). They are two green plug in connectors under the black plastic cover in front of the turbos in the engine bay. If memory serves, they are greenish colored, looked like electrical connectors (duh, probably cause they are), and if they are reconnected in flipped positions you get exactly what you got! I had it but "unflipped it."

My boost pattern was EXACTLY the same (BTW, so was another list members). When Cam worth went "ah ha," pulled off the cover on mine, and flipped the connectors all was freakin fantastic! One of the connectors has a dot or a number on the male connector that matches the same dot or number on the female connector- the other does not. You should be able to tell just by looking. This is one of every Mazduh Dealer's favorite f--k ups- some pro's too!

_____________ Date: Thu, 13 Apr 2000 15:56:40 -0700 (PDT)
From: Jay (styk33@yahoo.com)

> Check the turbo harness connections (whats the right name for these list
> people?).  

The one on the left is the precontrol and the one on the right is the wastegate control. This is, of course, standing in front of the car looking into the engine bay.

Date: Thu, 3 Feb 2000 07:56:22 -0800
From: "Hutchings, Spencer" (shutchings@vns.net)

< A HREF="http://www.geocities.com/spencerhut/rx7/turbo.html">http://www.geocities.com/spencerhut/rx7/turbo.html


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