Homemade Injector Tester/Cleaner

So you are a do-it-yourselfer? Boy, do Roy and I have a project for you. How about a fuel injector tester/cleaner so you can test and clean your Cosworth’s injectors? Sound like fun? Sound like a challenge? Well, read on.

Several Roundups ago Roy Linenbarger and I started talking about the Cosworth’s injectors. I wondered whether it would be possible to cobble up a system that would allow one to check them out. I had always thought it would be simple to make such a device, but never got around to seeing what I could do. Roy, who has figured out how to rework the 5-speeds in the Cosworth so that they won’t seize and grenade, agreed that it could easily be done. Intrigued, he promised to "give it a shot."

I waited eagerly for the next Roundup, in part to see all my old(er?) friends and in part to see what Roy had accomplished. Well, the answer was that he was still thinking about it, that the project was getting closer to the top of the list, and not to despair, he’d make it happen.

This year he delivered. He reported that he had assembled a test unit, that it worked, and that it wasn’t all that hard to build. "Did you bring it with you?" I asked hopefully. Sadly no. He had been working on trying to find a way to refinish the engine-turned aluminum dash bezels, and he had come remarkably close to perfection. He brought several test samples to the Directors’ meeting, and they generated extensive discussion. But the injector tester was nowhere to be found. He did promise me pictures, however, and this month he delivered. 

Homemade Injector Tester/Cleaner

Based upon a close inspection of the photos and conversation with Roy, I can report that there are essentially six sub-systems in his simple but effective device. They are:

Fuel Pressure

Fuel Transport


Power/Electrical Connections



Let’s take them in order.

Fuel Pressure

First is fuel pressure. We need some way to duplicate the fuel rail pressure of the Cosworth. Measurements in the field indicate that 32-39 psi is a good working range. So, we need an electric fuel pump capable of delivering that kind of pressure. Pretty much any fuel pump from a modern car will work (Roy used a stock in-tank pump from an ’87 Mustang rated at 23.3 gph), so use whatever you can find easily. Or use your spare high pressure Cosworth pump. It will work just fine.

One more piece. The fuel line pressure needs to be regulated. Otherwise, as Craig can tell you, the pressure will build to more than 70 psi. Here again any fuel pressure regulator should work, but for ease of use, borrow the one from your Cosworth’s EFI. Simply hook it into the fuel line after the fuel rail. You can ignore the vacuum connection and it will work just fine for, as Roy points out, at full throttle there is not much more vacuum than 1 hg of mercury. If you are interested in accurate flow rates, use any commercially available vacuum pump (e.g. the kind used to bleed brakes) and a vacuum gauge. If you are going to this much trouble, plumb a fuel pressure gauge into the fuel line after the fuel rail and before the regulator.

Fuel Pressure Regulator and Gauge

Close up of Four Injectors Under Test


Fuel Transport

Now that you can generate regulated fuel pressure, you need to get it from your fuel can to the fuel pump to the fuel rail to the regulator and back to your fuel can. Start with any heavy, safety approved fuel container.

 Roy uses a small can, 

but he and I both know that this is not particularly safe. 

Do as we say, not as we do, is our motto.

Unless you have chosen to use a high-pressure pump of an in-tank design, simply use standard fuel hose to move the fuel from the can to the fuel pump. Mount an external pump lower than the level of fuel in the can to ease the job of the pump. Many, including the Cosworth’s pump, are not self-priming, so be prepared to provide some assistance.

Next, use high-pressure hose to move the fuel from the pump to the fuel rail, and from the fuel rail to the fuel pressure regulator. You can use standard hose to move the fuel from the regulator back to the can. At about $5 per foot, you don’t want to buy any more high-pressure hose than necessary.


You will need something to hang all of your paraphernalia on. Roy used some spare lumber he happened to have lying around. Use whatever you have. You can go to the trouble of painting it if you wish, as did Roy, but since this contraption will hardly ever be used, just slap something together, but make sure it is sturdy and stable.

Power/Electrical Connections

Next is power. You will need twelve volts to operate the pump, and can use the same twelve volts to cycle the injectors. If you don’t have or want to purchase a spare automobile battery, a lawn tractor battery will work fine. Though you could use jumper cables from your Cosworth’s battery or from the battery on your wife’s car, doing so is NOT RECOMMENDED. The cables could be jostled and slip and cause a spark. Whatever your hookup, just be sure to make and securely tighten all connections before you bring your fuel/cleaner/test liquid to the party.

Roy has three switches in his design.


 One powers the fuel pump and two injector switches. One injector switch is a button switch for applying power in short bursts. The other injector switch is a toggle switch and is used when cleaning or examining the spray patterns. You could add to this design an on/off switch for each injector to provide additional flexibility, though Roy simply unplugs the injectors he does not want to open. 

Make sure all wires are solidly connected. You don’t want any sparks during the testing or cleaning process.

The best solution for getting power to the injectors is an old Cosworth wiring harness that you have cannibalized for the connectors to the injectors. Lacking that, see what you can find in a junkyard. Many injectors utilize a similar pin configuration, so you shouldn’t have too much trouble. Roy used a GM V-6 wiring harness from the late 80’s. He reports that the spade connector spacing was identical, but that the connectors had to be filed down a bit in order to fit. 

GM V-6 Connector Adapted


Finally, you need to collect the fluid you run through the injectors. Though Roy fabricated his own, a wallboard joint compound tray (aka mud pan) made of stainless steel and used by drywallers, commonly available at lumber yards and Lowes and Home Depot for about 10 bucks, makes a serviceable catch basin.

Mud Pan
A mud pan holds joint compound when you're taping and smoothing joints. It's also handy when you patch walls, which everyone has to do sooner or later. The straight edges of the pan provide a surface to clean your knife on between strokes.

Alternatively, you can use a set of four graduated cylinders to enable you to quantify your flow rates and compare injectors. Observe how ingeniously Roy mounted his glass cylinders.


Roy is using mineral spirits laced with carburetor/injector cleaner to test and clean his injectors. He chose this blend as he did not want anything too flammable, and also did not want something that smelled bad. Chevron’s Techron is generally regarded as the best injector cleaner on the market. Most good injector cleaners have Techron as their key ingredient.

Remember to use this contraption in a well-ventilated room or, preferably, outside. It goes without saying, NO SMOKING. 

It also goes without saying that you must have a helper and a fire extinguisher rated for gasoline type fires handy.

A Few More Points

If you look carefully at the photos of Roy’s tester, you will see that he has two fuel rails. One is a stock Cosworth injector rail. The other is for late model Ford and GM injectors. He fabricated a custom fuel rail for the non-Cosworth injectors with the thought in mind that he might want to try more modern injectors on a Cosworth someday, and this will enable him to experiment with spray patterns and flow rates.

Roy also notes that his collection tray and his graduated cylinders can be swapped from side to side as needed. He only runs one side at a time, and swaps the hose connections depending on which fuel rail he needs to use.

Finally, Roy notes that the pictured injectors were removed from a car with a hole in the side of the block. They had not been run in the 8 years he had them, were partially clogged, and that "every time they are run with solvent they have improved."

He concludes that "they might be savable." A man after my own heart!

As you can see, you too can build your own injector tester and cleaner. A few hours in the garage and a few spare parts, and perhaps a trip to the junkyard, could save you up to $60 per injector, or as much as $240. Think about it.

" $240? I could buy the wife....nah, new
Yoko's at tirerack.com "