Injector Cleaning

Last updated: April 26, 2000

The following was exerpted an article in Grassroots Motorsports, by Tim Suddard.

Understanding Fuel Injector Cleaning, Balancing and Blueprinting


Injector blueprinting is a recent buzzword that has been much talked about in racing circles. What does this term-along with related terms like injector cleaning and balancing-really mean to you and your fuel-injected performance car?

Essentially, what blueprinting means in relation to injectors is controlling the spray pattern. This involves studying the spray pattern, often with an oscilloscope, and trying to match the pattern from one injector to the next. Matched injectors should yield matched performance.

Balancing is the process of measuring the flow of each injector. Each injector should flow within a couple of percentage points of the others for optimum performance. We would love to tell you that it takes amazingly sophisticated equipment to measure this, but essentially it's about as complicated as peeing in a cup. The injectors are placed on top of a metered cylinder and fired for about 30 seconds; the output of each injector is then measured.

A very common misconception in the performance world is that bigger injectors are always better. Balanced and blueprinted spray patterns are much more important to engine performance than greater flow available from bigger injectors. Yes, if you increase your air flow and exhaust system and make other modifications, you can go to bigger injectors, but still you need to have balance and an even spray pattern.

This simple flow test can have its limitations. As Tim Marren points out, what happens in 30 seconds on the bench is materially different from what happens in a hot car after hours of endurance racing. According to Ohm's law, as heat increases so does resistance, so your injectors may perform differently after a two-hour enduro. Nobody can duplicate this scenario on the bench, but Marren performs his tests at 130 degrees Fahrenheit to begin to simulate the effects of heat.

Injector leakage is another very important consideration. Often a faulty injector will continue to leak fuel after you have shut off the engine (remember, you still have fuel pressure even after you turn the car off). Next time you start the car, there is raw fuel sitting in the cylinders. This is very hard on an engine. A competent injector tuner will detect any leakage and either repair it through cleaning or advise you to replace the injector.

Cleaning an injector is done in two steps. First, a solvent with similar properties to gasoline (except for the flammability and propensity to evaporate) is run through the injectors. Next, the injectors are cleaned ultrasonically (the same way jewelry is cleaned). Generally this process can take a clogged injector and get it back to nearly 100 percent efficiency.

So what clogs an injector? The first thing is gummed-up gasoline. If your car has sat for extended periods or if you buy a junkyard engine, there's a good chance that the gasoline left in the injectors during storage has turned to varnish or a solid state. This will clog your injectors. Another source of trouble is water. Often found in fuel to varying degrees, water will cause rust if left in an injector for any time. Foreign material (dirt) of one kind or another is the third thing you need to watch out for. Yes, your car has a fuel filter, but no, it doesn't get every microscopic particle of dirt out of the fuel system. Chemical deposits also build up over time in your injectors.


Getting your injectors serviced is as easy as removing them from your engine and shipping them to an injection tuning company using the delivery system of your choice. For your benefit, you should number each injector so you can tell which cylinder it came from; this will be good to know because the tuner will most likely supply you with a computer analysis sheet showing the injectors' condition before and after the service.

The best way to deal with these guys is to send them two sets of injectors and let them tell you which four, six or eight (or 10 or 12, if you have a Viper or Jaguar) flow the best, have the best spray pattern and are most closely matched to each other.

Tim Marren explains the process: "We take the injectors and we flow them as they came out of the car to get a baseline for the condition of the injectors. We then download the information into the computer with the flow rates in cc per minute. We check the spray pattern and then reverse flow the injectors to see if there were any contaminants in the injector. Once we're finished with that, we strip the injector down and ultrasonically clean the injector. This is the new, high-tech way of cleaning the metal ultrasonically and at the same time we're pulsating the injector with a programmable fuel management system to open and close it at a desired pulse width. As the injector is opening and closing, we are ultrasonically cleaning it. This rids the injector of any wax or varnish buildup on the injector to increase flow, which is critical under high rpm in relation to horsepower, and to increase fuel atomization, which controls your torque rise in the motor.

"Once that process is completed, the injector is checked to make certain all the cleaner is out of the injector. It is then brought up to operating temperature and we strobe the injector, checking fuel atomization by watching the opening and closing time of the injector with an oscilloscope, to make sure the electrical windings in the injector are correct and everything is operational. Three hydraulic tests are performed after we're done ultrasonically cleaning them, and the key is for all the injectors to be within a zero-to-one or -two percent deviation of one another. They should not exceed a four-percent range between one another."

This service normally takes less than a week. Overnight service is available from all three companies. Marren charges $23.75 per injector; this includes new O rings and seals. RC Engineering charges $24.00 each or $28.50 with new paint, O rings and seals. They do not do mechanical injectors. Performance Diesels charges $25.00 each without new O rings and seals.

We have used all three of these companies and have been satisfied every time, both with their work and their service. All can assist you with fuel injection modification and sell you new and bigger injectors. RC Engineering also modifies throttle bodies for increased airflow.


At this point, you may be tempted to expect an injection tuning shop to miraculously increase your engine's power and efficiency. This may or may not be reasonable, depending on what you start with. They cannot improve upon a perfect new set of injectors. What they can do is assure you that your injectors are up to snuff. (How else would you know?)

Usually they can help the average Showroom Stock racer slightly. If you have a 20-year-old fuel-injected car, having the injectors inspected and repaired could probably help you a lot. These guys can usually bring an injector that is not too far gone back to nearly 100 percent. If an injector is junk, they can sell you a new one that has also been checked to make sure it balances with your other ones. Either way, at about $25 per injector, it's worth knowing no matter what you drive.


There are several places to go if you're interested in optimizing the performance of your injectors. Marren Motorsports, run by Tim and Nancy Marren, has been cleaning, balancing and blueprinting injectors for years. They have a very long motorsports history and are currently involved in SCCA Showroom Stock racing with several Neons.

Russ Collins runs RC Engineering, a West Coast shop famous for Honda engine building. In the last 10 years Russ, who got his start in top fuel drag racing, has also become very interested in fuel injection modification.

In addition to these well-known injector tuners, you might also check around for a source near you. Recently we took a set of BMW 535i injectors to our local fuel injector guru, Ron Brothers of Performance Diesels in Daytona Beach, Fla. Ron got interested in fuel injection modification when he began building an electronically programmable fuel-injection system for his 12-cylinder Jaguar.


Marren Motorsports
500 New Haven Ave. #1059
Derby, CT 06418-2527
(203) 732-4565

Performance Diesels
1187 State Ave.
Holly Hill, FL 32117
(904) 253-0383

RC Engineering
1728 Border Ave.
Torrance, CA 90501-3601
(310) 320-2277

Date: Mon, 28 Jul 1997 07:40:34 -0400 (EDT)
From: (Bret de Pedro)

The best way to get your injectors cleaned is to remove them and send them out to cleaned and balanced. In order to remove the injectors you will need to remove the upper intake manifold to get to the primary injectors. When you remove your injectors mark each one primary one, secondary one etc, this way when they come back you will have a print out of flow and spary pattern before and after cleaning. The best place I have found to do the cleaning is Marren Motorsports in Connecticut, their number is 203-732-4565 and ask for Tim.


Date: Wed, 17 Dec 97 14:03 PST

There has been some discussion recently about injector cleaning recently. Since I have the turbo off my car at the moment, and the injectors are easy to get at, I decided to have them sent out to be cleaned and flow matched. I sent my injectors to RC Engineering in Torrance, CA. (310.320.2277) The total cost of the cleaning and flow matching was about $120.00. They turned my injectors around and got them back to me in just a few days.

The biggest pain in this whole operation was extracting the injectors. Damn rubber o-rings hold those thing in tight !!!!

RC Engineering included a computer printout on the injectors, broken down by types, which I thought might be of interest to some list members.

3rd Gen motor have 2 sets of injectors, one set running at 850cc/minute (the primaries if memory serves me correctly), and another set running at 550 cc/minute. Each pair of injectors were cleaned and flow matched/balanced with its mate. The injectors from my car are the originals and to my knowledge have never been out of the car. The have 45K miles on them. Each set have a before and after set of readings plus some theoretical HP deliver capabailities of each set.

For the 850 cc Injectors - test performed at a test pressure of 43PSI


        Before Cleaning              |            After Cleaning
INJ#      CC/Min     Pattern         |     INJ#     CC/Min     Pattern
  1        834.1     Fair            |       1       870.0     Excellant
  2        852.0     Good            |       2       870.1     Excellant
HIGH : 852  Low 834.1 AVG: 843.1     |     HIGH: 870.1 LOW: 870 AVG: 870.1
TOTAL SYS. LBS./HR - STATIC: 160.58  |     TOTAL SYS. LBS./HR - STATIC: 165.72

- ------------------------------------------------------------------------------
@B.S.F.C. of .65: 197.6              |     @B.S.F.C. of .65: 204.0
@B.S.F.C. of .55: 233.6              |     @B.S.F.C. of .55: 241.0
@B.S.F.C. of .50: 256.9              |     @B.S.F.C. of .50: 265.2

For the 550 cc Injectors - test performed at a test pressure of 43PSI


        Before Cleaning              |            After Cleaning
INJ#      CC/Min     Pattern         |     INJ#     CC/Min     Pattern
  1        549.0     Fair            |       1       560.0     Excellant
  2        549.2     Good            |       2       561.2     Excellant
HIGH : 549.2  Low 549.1 AVG: 549.1   |     HIGH: 561.2 LOW: 560 AVG: 560.6
TOTAL SYS. LBS./HR - STATIC: 160.58  |     TOTAL SYS. LBS./HR - STATIC: 106.78

- ------------------------------------------------------------------------------
@B.S.F.C. of .65: 128.7              |     @B.S.F.C. of .65: 131.4
@B.S.F.C. of .55: 152.1              |     @B.S.F.C. of .55: 155.3
@B.S.F.C. of .50: 167.3              |     @B.S.F.C. of .50: 170.8

OK, Looks interesting. This all makes sense to me except for I hope somebody out there can tell me the sigificance of "LISTED BRAKE SPECIFIC FUEL CONSUMPTION" means. I presume the one number implies the horsepower that the given injector set can support at the test fuel pressure. For example, for the 550 cc injector set after cleaning we have, @B.S.F.C. of .50: 170.8. I take this to mean that the 170.8 is the horsepower rating this set of injectors can support is 170.8 theoretically. I have no clue what the .5 number means. If anyone knows, please let me know.

So, all in all I think that if I add the two horsepower ratings together (170.8 + 265.2), my injectors could deliver enough fuel at an %80 duty cycle and a 43PSI pressure at the fuel rail to support a theoretical horse power rating of 436 H.P.

Interestingly, the 550 cc injectors, while able to deliver more fuel after cleaning, ended up more out of balance than before the cleaning.


From: Max Cooper (
Date: Saturday, April 22, 2000 8:24 PM

I had my stock injectors serviced at RC Engineering this week. They had 92,000 miles on them. I almost always use name brand premium gas (including totally clear Amoco Ultimate while I lived in Michigan). Here is what they found:

Inj   Nominal      Pre-clean      Pre-clean      Post-clean     Post-clean
#     flow rate    flow rate      pattern        flow rate       pattern
===   =========    =========      =========      ==========     ==========
1       550          537.3          GOOD           540.4        EXCELLENT
2       550          526.7          FAIR           541.0        EXCELLENT
3       850          832.3          GOOD           840.5        EXCELLENT
4       850          826.5          FAIR           840.0        EXCELLENT

All flow rates reported in cc/min. At worst, this was like having -2% dialed in on my PFS PMC -- a 2% reduction in flow rate versus their flow rate after cleaning. The spray pattern is surely important, too, though probably more for drivability. I'll keep you all posted to see if my 3K hesitation returns, though I am experienced enough not to get my hopes up ;-). They were not too bad as they were, they are in great shape now,


Date: Sun, 23 Apr 2000 21:19:38 -0400
From: "Wade Lanham" (

Injector flow test after 47K miles.

I sent mine out a couple of weeks ago to RC engineering also, so I thought I'd report my results as well.

1       550          533.4          FAIR           570.3         Excellent
2       550          564.5          GOOD           571.2         Excellent
3       850          863.5          GOOD           871.2         Excellent
4       850          863.5          GOOD           870.7         Excellent

Worth mentioning is the data on Cirian's site, where someone with an appx 45k mile car had results similar to mine. Either Max's have lost flow capacity with age, or his flowed a bit less from the factory. A few more samples and we should be able to make a pretty safe assumption. I know there is at least one other person on the list who just sent his out.


From: kevin kelleher
Date: April 23, 2000

Since you plan on running higher fuel pressure with a RRFPR, vs 2.5 bar stock (and RC test pressure), you may want to have RC test them at 3 and 4 bar to be sure they are linear up there.


Date: Wed, 17 Dec 1997 16:21:44 -0600
From: "Kevin T. Wyum" (

To answer your questions Mike and a few observations,

The 850cc's are the secondary injectors.

The BSFC's listed are a tad too low for us. The number that floats around for rotary's is .7. The number is the pounds per hour of fuel that it requires to make one horsepower. So you convert from cc/min to lbs/hr and then divide your total fuel flow by the BSFC and multiply that by the duty cycle you will use. That will give you the max supportable horsepower your injectors can support.

Also of note is that the test psi of 43 is a tad high for us. The baseline fuel pressure for a 3rd gen is 40 psi with an additional pound per psi of boost which keeps the differential across the injectors the same.

Hope this helped. BTW I use 6 x 850cc injectors on mine which comes out to 486 pp/h. Now divide this by .7 BFSC = 694.54 and multiply by duty cycle of 85% for me to compensate for the fact that A. I will run beyond 80% and B. run at a higher pressure. This comes out to be about 590 HP or so, which is right where I am expecting to be. Although I should note that the .7 is probably pretty rich even for us. Consider it as a safety margin for tuning. This is evidenced by the stock configuration only supporting 306 hp and we all know that's a little low. A number of about .6 is probably better. Another issue is that injectors flow volume, not weight. The pounds per hour conversion assumes a relatively light fuel where as most racing gas is more dense. Lastly this should also explain why racing fuel helps a lot wih the stock fuel system. Not only is it more dense but also allows a lower BSFC to be used because you can run leaner without detonation.

Date: Mon, 24 Nov 1997 22:58:58 -0700
From: "Nowhere Man" (

Since there has been a lot of talk about F.I. cleaning, I decided to post this little snippet.


Service bulletin #001/93, Category F

Applies to all fuel injected models

To improve fuel injection performance, Mazda has tested and approved a highly effective fuel injector cleaner. The kit and cleaner is recommended for all Mazda fuel injection systems. Mazda's fuel injector cleaner uses a chemical reducing agent rather than the common solvent used in typical aftermarket cleaners. As a result, in tests against aftermarket competitors, Mazda's cleaner outperformed all others and was the only one to restore the fuel injector's flow rate to original factory specs. Mazda recommends cleaning injectors every 15,000 miles.

DESCRIPTION             PART#             REMARKS
Fuel Injector Cleaner   0000 77 2019      case of 12 cans

Tool kit                0000 77 2026      w/ instructions
                        (req'd for use with the cleaner)

Service brochures       9999 95 043N 92   QTY: 1 package = 50


Date: Mon, 24 Nov 1997 16:21:17 -0500
From: Tuck

>I remember reading somebody post a message about
>the best way to clean these things is to pull them
>out, add a little voltage to open them up, and then
>spray some carb cleaner backwards through the injector.

Well, first off, I did specifcally mention a prodcut by name, which was Gumout tuneup spray (which is for fuel injected cars rather than carb cleaner). The included nozzle with the tuneup spray is precisely the right size to just wedge into the injector nozzle and give an acceptable seal.

Applying voltage was a real half-assed effort on my part, I took the battery out fo the car, striped the ends of two pieces of wire, coiled two ends on the battery posts and then touched them to the injector contacts while spraying crap through them backwards. Not exactly an elegant way of doing it, and it certainly required its fair share of dexterity. The RIGHT way to do it is to get a 12V power source of some sort (I doubt it matters how much current it can deliver given that an injector can't draw that much) and use alligator clips to apply voltage to the contacts while holding the injector in some sort of vise. Even better would be to buy an injector harness plug from digikey or the like and make a little rig specifically for doing it. But by the time you get to that pointm, you might as well send the injectors off to a place like Marren (who did my injectors - balanced, cleaned, etc.) and pay the 25 each or whatever.

Be aware that when you apply a constant 12V to an injector you are effectively driving it at 100% duty cycle, which can make them heat up, so apply the voltage, spray the crap through, and disconnect the voltage. Don't just leave it sitting there with voltage applied to it.

DIY Electronic Fuel Injection - in case you want to roll your own.

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