Passing Emmissions

Last updated: April 7, 2002

Date: Fri, 14 Aug 1998 07:52:33 -0700
From: Spencer Hutchings

Two most common things that will fail any car, modded or not. Bad plugs or plug wires.

  1. Brand new plugs the day before the test. Everyone should do this even if you think your plugs are fine.

  2. Brand new or known good plug wires. Ditto.

  3. You do NOT need the pre cat, unless you get tested for cold start emissions. Even CA doesn't do that, yet.

  4. It is possible to pass CA emissions without either cat. See below.

  5. You must have the air pump hooked up even without both cats. It shoves just enough clean air into the exhaust to squeak you by. I did not try this. The information is from Tri-Point they have done it and does work. The Pettit Mid Pipe has the fitting so you can run the air pump line to it.


Date: Mon, 27 Sep 1999 19:26:08 -0400
From: "Rob Robinette" (

Changing the plugs can't hurt. Try some of the pre-emission test fuel additive, Pep Boys and most other auto parts stores sells one brand or another. Then try it again and make sure the car is really warm before they sniff it. If you have to, have them run the car at about 4000 rpm for a couple of minutes before they start the test. How old is your air filter? Replacing it could help too. Have you done any highway driving lately? Some nice steady state highway driving might help blow out the main cat enough to get you through the test. Good luck.


Date: Thu, 9 Apr 1998 14:07:13 -0400

>I have an ASP exhaust, w/ no main cat. I saved my stock exhaust w/
>cat for the smog check (not due for 2 years).
>My question is this - if I remove the airpump, would I need to put it
>back on to get the main cat to function properly? I know it injects
>air to help the process, but is it absolutely necessary to passemissions? Would it read high but still pass?

This one is simple, since I have TOO MUCH experience passing mod'ed 3rd gens emmissions (just ask Dean Colver or Dave Girvan). The formular is simple but inflexible:

Legal 49 state emissions = Stock injectors + Airpump + ACV + Main Cat

- (the secondary air DOES NOT HAVE go to the main cat (split air). It will pass with it going soley to the exhaust port (port air).

- notice the intention lack of catback


Date: Thu, 9 Apr 1998 21:04:14 -0400

>However, if I stick in the ASP race IC, I don't think the
>airpump will fit back in there.

Do what I did... make your car an NA!

Yes, I removed the plumbing from the turbo outlet to the throttle body (TB) elbow. On the TB elbow, I mounted a K&N filter, secured a sock over the turbo Y-pipe outlet, and defaulted the turbos to spring boost loads (so they wouldn't over spin). If your still using the stock boost control, just cap off the hose going from the wastegate solenoid, and the system will default to the wastegate actuator spring actuation (open at 7-10 psi). With the extra room, putting the airpump in is not a problem.

Assuming the bolt connecting the both ends of the midpipe are not seized, swapping out the midpipe for the main cat should only take about 20 - 30 minutes once the car is on jacks. Removing the IC and attaching intake tube should take but 20 - 30 minutes. The airpump, airpump output hose and belt will take the longest at about an hour, and the elbow filter and turbo output sock shouldn't take more than 30 minutes. So add it up, and I think you're in the ballpark even with a worst case scenario.


Date: Fri, 10 Apr 1998 00:28:11 -0500
From: tom

Airpump is a quick and easy 10 mins. putting the stock pulleys back on the other shafts might be tough. I think r&r of the cat would be a bigger pain. Don't think it's a good idea to run cat w/o air, but I'm not positive about that. At least we only have to do it every other year...


Date: Fri, 10 Apr 98 07:40:50 -0500
From: "Linthicum, Sandy"

At least a couple of hours for anyone other that a Pettit/PFS or other hardened expert.. You must remove both belts, put on new belt and maybe pulleys, reinstall air pump and the associated pieces of hardware (numerous), etc. and get it all back together and working.

Took me many hours (over 4) just to take it off, retrofit pulleys, belts, and other block off parts and get everything ship shape. The air pump stuff weight an easy 20lbs.


Date: Sun, 12 Jul 1998 10:31:10 -0700
From: "Drew"

Smog Check II is here in CA and creating great challenges for everyone.

If you have an 3rd gen:

1. Empty the catch tank located on the underside of the throttle body/intake elbow, use an air compressor. This little tank was full of fuel and would purge when the engine was ~3000 RPM's...and would drive the HC's through the roof!

This little problem cost me $180 to car was the test case for Keyes Mazda (Excellent FD service and knowledege, just expensive). They had three other FD's with the same exact symptoms, hopefully they charged them a lot less after me.

2. Have your Shop manual or Service Highlights handy, so the techs will believe you when they cannot find the EGR valve or evap. tank. There is a special order from Consumer Affairs releasing the shop's responsibility for a visual on the FD EGR. The evap tank can only be visibly checked from underside of the vehicle, located to the front of the gas tank on the LH side.

3. Call ahead to the test station and make sure they have the upgraded RPM sensor for the rotary. Make sure they have tested a few rotary's or you will be sorry. The standard RPM sensor will double the engine RPM's and the older rotary sensor will NOT usually read the FD (and some FC's) engine RPM's. ESP equipment is the most popular and the most cranky when it comes to rotary's.

4. Do not allow the car to cool down more than an hour before the test.

5. Conduct a pre-test (a lot of the FD's are getting labeled as Gross Polluters).

6. If you become a gross pollutor...Just take your car to the nearest DMV Referee shop when it is time for the next re-test. Don't waste your time with an indepedant shop. The Ref shop in Northridge, CA is very decent and cost $30 + cert.


Date: Sat, 25 Mar 2000 18:57:59 EST

On US models, there is a small, pencil shaped "catch tank" immediately in front of and below the throttlebody, i.e., approximately where the sweeping elbow and throttle body meet. There is rubbing tubing going into and out of this catch tank, which is inline with the gasoline vapor collection system.

The catch tank periodically does a solenoid activated "dump" which pours accumulated vapors into the running engine. If this occurs during your emissions test, your car will fail.

Some have blown out the catch tank with compressed air shortly before the emissions test. I simply disconnected the rubber tubing at one end (towards the front of the car, I think) and temporarily plugged it. I then drove to the testing center, where my '93 easily passed the IM240 dyno test.

Afterwards, I removed the plug and reconnected the tubing to the catch tank.


Date: Fri, 14 Aug 1998 09:11:49 -0400
From: Demetrios Karagiannis

You can pass with the precat off. With the PMC you can get a car to pass with no cats if you tune it right. Give Peter a call maybe he can give you some tuning suggestions.


From: Steve Cirian
Date: February 22, 1999

>>I am ditching the airpump.  I talked to Carlos Iglesias about how to 
>>pass emissions w/ all of this crap on, and he said to go NA (normally 
>I would think that would make it run rich, no?  (or at least require a PFS
>PMC to adjust AF ratio.)   He put his main cat on, no precat (but might 
>not pass visual).
>They won't even know what a precat is.  I was toying with running a line
>from a compressed air tank to the (temporarily reinstalled main cat) and
>using a bleed valve to supply it w/ air, negating the need to temporarily
>reinstall the airpump.

I thought about the compressed air idea too. Carlos does have a computer, I think, so I don't know if he had to fool with it or not. But since the O2 sensor is in the downpipe, shouldn't it sense that the engine isn't getting as much air (from the turbos), and reduce the gas as well? My other idea is that since I live about 2 miles from the test station, is to just try it w/o the airpump. I know the catalytic reaction won't be as efficient, but it still might pass anyway. The drive it 2 miles home. It shouldn't damage the cat in that brief amount of driving if I take it off right away. I was wondering if the cat might work better if you got it really hot, like drive over with the car revved up to 5 - 6K the whole way. If it doesn't pass w/o the airpump, then you always get a second chance (and a third and a...).

>The fools running the test don't even open the hood (probably wouldn't know
>how anyway)  they used to just rest an rpm sensor on the hood and stick the
>sniffer in.  Even my 79 [1] with heavy blue smoke would pass. NOW
>TREADMILL.  I REALLY don't like the idea of one of these idiots driving my
>car 1 inch.  There is an opt out clause for lowered cars that can't go on
>the treadmill.  I'll have to ask around, maybe thats a good excuse to get
>coil over adjustable ride height setup like you.

There is no way my car would go onto a treadmill if there is any sort of a ramp leading up to it. It scrapes bottom (I think the exhaust) going into my garage, which has a small rise up from the alley. I need to jack it up and see what is scraping. I need to change the oil this weekend anyway, so I will check it then. I can't even get a low profile jack under it without first driving it up onto mini ramps I built for this purpose.

The BEMs at the check statio have no idea what they are doing, especially when it comes to the rotary. The RPM sensor they use needs to be told how many cylinders you have. We don't have cylinders, as you know. So they usually use 6 cylinders. I was wondering if I told them that the rotary was equivalent to a 12 cylinder, if it would get me a wider acceptance range, so if the car is running dirty it would still pass?

(BEM = Booger Eatin' Moron)


Date: Sat, 05 Jan 1980 06:48:50 -0600
From: tom (
Subject: (rx7) [rx7][3]how to pass the IL IM240 emissions test w/heavy mods

Failed the first time even though I put the cat and airpump back on.

To leave the intake in place for the test, I had to bypass my ASP IC (and remove it) with some old oem piping parts, so I ran w/ no IC at all. I would recommend the M2 S pipe so you can leave the airpump on the car at all times, but I didn't have it.

Make sure you have the fan mod or another means of controlling the fans, because the car will run hot during your pre-drive and test.

Disconnect the catch tank that leads to the evaporative charcoal canister under the intake elbow and plug the manifold side (so you don't have a vacuum leak) and put a hose on the canister that hangs below the engine so no fuel can come from the canister and get on the hot engine.

Leave the downpipe on. swap your cat back in in place of the midpipe if you have one. MAKE SURE THE GROUND WIRE THAT GOES TO THE CAT IS IN GOOD CONDITION.

Hook up the airpump and its wiring, and run a temporary hose from the airpump intake to the front of the car so it can pick up cold outside air. Put a rag w/hoseclamp over the hose so it dosen't suck in any dirt. Remember, the airpump output goes to the bottom one of the 2 tubes freed up when you removed it. You will now get the moo-fart noise everyone complains about when they put on an intake.

Drive the car for at least 35mins, paying close attention to its behavior and maintaining water temp by using the fan.

The first test I failed, I left the parking lights and fan on during the test. Bad idea, as I later noticed on my J&S AFM that when there is any electric load on the car, it went to rich- this means you don't want to run the fans during the test either, but DO run them just before and after.

After driving the car for 35 mins, BRIEFLY stop in the office and ask who the best stick driver is. Make sure they will be the one driving the car.

Start the car and run it with the fans going for at least 5 mins prior to the test- you need to heat up the cats and start getting cross counts (oscillations) on your AFM.

Leave the car running while getting your gas cap tested.

When its time for the dyno treadmill part of the test, get in the passenger seat, and when the tester gets in the car, explain to him that his boss said he was the best stickshift driver in the place, and that you have a pretty high powered car here and that you need to explain a few things that will help the car pass the test.

The first person that I had drive the car lugged it in 5th from 1400 rpm up to 60 MPH.. During the acceleration phase of the test she invoked up to 2 PSI of boost, which made the ECU go right to the maps, which failed me pretty easily. Tell the driver to go VERY easy on the gas, that the car is strong enough to do the aceleration part of the test with almost NO accelerator pressure, and to try to watch the boost/vac guage and try to keep the vacuum between 10 and 20mmhg. Realize that this may be a challenge for the tester, as he will have to be following an accelleration profile on the monitor outside the car and will have to be looking at both simultaneously. Be conciliatory during the test, helping with the vac readout while keeping your eye on the AFM . When it goes rich, try to get him to ease up a little on the gas if the vac is getting below 10-8 mmhg.

On the 2nd run, my test was over in about 20 seconds, and I passed with HC and CO below 50% of the standard. Apparently the test only goes the full 240 seconds if the computer can't get a good sample or if it looks like its going to be a close call. Watch the temp guage thru the test and hit the fans if the temp goes over 220F., and DON'T FORGET TO TURN ON THE FANS WHILE YOU ARE GETTING YOUR PRINT OUT.

Keep in mind that I recommend running all emissions equipment at all times. The evap emissions system costs no HP, the airpump dosen't hurt at all during acceleration, the only thing that is a problem is the stock cat, which can be replaced w/ a hi flow cat at very little expense in HP. It would sure be a lot easier to run w/ full emissions (except a downpipe) at all times rather than going thru the hassle of swapping parts out every 2 years. I plan to go that route soon, but for the moment the car is driven so little that I can use it and not feel to guilty about the emissions


Date: Sun, 14 Feb 1999 18:19:31 -0500
From: RX-7fl (

I just passed my emissions test in Florida.

Here was my set-up:

N-tech fresh air intake system
stock cat
Pettit market exhaust
no air pump

Here are my numbers.

HC(PPM)   25    state limit 225
C0(%)    .10    state limit 1.2
C02(%)  15.3    no state limit

In Florida they don't check under the hood.


Date: Tue, 27 Jul 1999 10:54:57 -0700
From: Evan Burkitt (

When I had mine smogged, the technician told me he needed to be careful during acceleration to the test speeds to avoid boost, which evidently would produce too high a peak emission level (the machine records peak and average emissions at the test RPMs). If you live in the Orange County area, Costa Mesa Shell (714-546-7220) has tested [3]s successfully. Also, be sure the engine is fully heated up before the test. Leave it idling while you wait for your turn on the machine.


Date: Wed, 19 Jan 2000 15:16:29 -0500

Let me say first that any smog dyno test on the FD should be run in 3rd gear, below 2800 rpm, to achieve the load simulation conditions. Run any FD beyond 2900-3000 rpm, and it will flunk emmissions, period.

The PMC allows you to lean out the part-throttle and idle maps to any level desired. While this will not affect the car under closed-loop operation, it WILL affect emmissions during transient throttle events such as the smog dyno.

The PMC comes from PFS with an extremely rich setting, which has been programmed in through a global fuel enrichment input which is invissible to the PMC user. That was Peter's way of solving a variety of driveability issues. To prevent popping and sluggish throttle response on my car, I have removed up to 18% fuel in my PR-LL and PR-ML maps. DO NOT remove fuel from the PR-HL and WOT maps. You can also remove up to 6% fuel from your idle map. With this setup, my car passed the SoCal smog dyno test with flying colors, despite the fact I am running a downpipe and a center section with an HF cat in it (retained air-in from the pump).

I am not very diplomatic, so here goes: the HKS Fcon is JUNK. Don't use it on the FD.

"Funny thing is that we stuck the probe in that". "That", according to my understanding of your description,is your compressor bypass valve and should be open at idle. It should not, however be passing HC's

"He told me it's either the ACV or a check valve located by the main-cat. So whatever is happening my main-cat is not getting what it needs at idle to do the chemisty mixing...and it's being pushed back..."

If you have a Cali car or a North-East car, your EGR valve has a switch on it, which has been known to go bad. This results in an error code on the ECU and, more importantly, your cat may not get the air it needs to work. That is not a cheap fix, however, and requires removal of the extension manifold and intake plumbing to test for continuity at the switch and visually inpect it for damage. So I would suggest the PMC leaning approach as a first stab.


From: Lou Young (
Date: 08/06/2001 11:42 AM

Background: I live in Phoenix, AZ. I own a 3rd Gen with normal mods (intake, exhaust, no cats, mild-street port, intercooler, tiny-assed battery, no air conditioning, PFS Purple computer, pullies, J&S knock sensor, Walbro fuel pump, M2's rising rate fuel pressure regulator, a few other things, plus suspension and safety mods that have nothing to do with the engine). We have to pass an IM147 test every two years. I've never heard of an IM147 until now. The last time I tested we were doing IM240.

First Test Prep: I put the main cat back on the car, attached the air pump pipe (the air pump always stays on the car), then I leaned out the IDLE map with the PFS because I know it idles really rich.

First Test: I'm not sure they tested idle at all. We put it on the rollers and I got in the passenger seat. The test consists of the dude driving the car on the rollers and following a curving line on the monitor, plus shifting when the computer tells him to. He ran the line, I heard the exhaust pop once when he let off the gas to slow the car down (that can't be good), and it seemed like the test took forever. Then the computer gave him another line to run. Eventually it ended and I got notice that I failed. Here's the numbers:

HC:  01.27  Max Allowed: 00.80
CO:  12.76  Max Allowed: 12.00
NOx: 01.41  Max Allowed: 02.00

Second Test Prep: Changed plugs, disconnected fuel catch tank thingie under the throttle body, and used the PFS Purple computer to lean out part throttle fuel and idle. Here's my PFS numbers:

IDLE: -10%
RPM: 2200  4000  6000  7800
LL:  -18%  -18%  -16%  -14%
ML:  -16%  -16%  -14%  -12%
HL:  -14%  -14%  -12%  -10%

Second Test: This time I pulled onto the rollers, turned off my fan switch, flipped off the radio (I left the fan on the first time). I asked the guy to try to keep the vacuum needle under the 0, but he gave me the spiel about having no control over what the computer wants him to do. Blah, blah, blah. I said, "Just try not to be too agressive." He ran the line, I watched the vacuum gauge (which never went above -4 inches), and the A/F meter hardly ever went rich. During coast it didn't read anything at all. He ran the test for about 15 seconds, then the computer told him to stop. He turned to me and said, "It was pretty short. That's a good sign." Here's the numbers:

HC:  00.22  Max Allowed: 00.80
CO:  04.41  Max Allowed: 12.00
NOx: 00.89  Max Allowed: 02.00

To pass, I basically did whatever Ciriani's site said to do...

Date: Wed, 27 Jan 1999 16:28:34 -0800
From: "Drew" (

The most important THING you can do is to empty the catch tank that is mounted belown the TB. It gets full of fuel and lets off emissions at that range... Use an air compressor.

It only cost me about $750 to figure out this take advantage of it.


Date: Tue, 18 Jan 2000 16:35:41 -0800
From: "Drew" (

> Fails NC emissions inspection horribly, even with rotary
> mechanic trying to force it to pass (revving, several test runs, and
> even tested a convenient new boinger to verify operating status of 
> analyzer)
> Results, all lowest attained:
>    HC 1583 (hit 4000ppm+) which is the main concern.....get this down and
>    the others should pass too
>    CO   5.28
>    CO2 11.30

Sounds like the catch tank is full. Empty it and you will pass like a football.


Date: Thu, 6 Apr 2000 19:31:47 -0700
From: "Derek Vanditmars" (
Subject: (rx7) [3]Fuel Vapour Recovery Parts

Since I tested my relationship with the Mazda parts guy the other day trying to find these parts on the lame diagrams with even lamer descriptions for the parts. I would like to share with the list the part numbers for fixing this.

Typical symptoms are failing idle emissions and having very to failing dyno-test emissions, also running rich at idle. The one-way valve is a small aluminum unit and the solenoid valve bolts in front of the ignition coils, both are very easy to get at once the alternator is removed.

NF01-13-890 One-way valve
F285-18-741 Solenoid

Date: Tue, 19 Jan 1999 21:23:18 -0800
From: Johnny and Tracy (

OK, at the moment I fail at idle but pass at 2500 rpms....(no dyno in my area)

My split check valve (by the main cat) is air coming from split valve hose at 2000 rpm...I wish hoping this was the problem, cause it very simple to fix.

Other test involved checking the check valve (port air) in which you disconnect the ACV hose to the airpump and let idle. Well I get exhaust coming out of that guy so that tells me the port air valve is no good.

It so happens to be deep in the extension manifold behind the ACV...Its covered under the 7/70 CA emission warranty...but still now I have to go though putting the damn pre-cat back on !... Atleast the mechanics wont have to do too much diagonostics...I think I already figured it out for them, unless some other solenoid of something is wrong, but they should be able to check that too, once the manifold is off.

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