Your engine is running rough, or maybe the idle speed varies up and down. Several friends in your local Fiero club have similar problems. Could it be bad injectors? How can you test them quickly and cheaply? Here's a setup for you or perhaps for the whole club. (This would make a great club meeting "Tech Session".)

This Rube Goldberg gizmo is something only a gearhead could love. It's crude and cheap but effectively tests fuel injector flow rate, leakage, and spray pattern. The setup DOES NOT improve injector performance except perhaps by coincidence or if injector cleaning products are used. There are many details that can be improved, but ours has performed flawlessly as-is since 2001.

For safety reasons we use kerosene instead of gasoline for the test fluid. Kerosene has different fluid characteristics than gasoline and the flow rates may not be the same; we suspect they are similar. It is feasible to use an injector cleaning fluid in place of kerosene but we haven't tried it.

Compressed air is used to provide motive pressure. We set the pressure on our air regulator to 40 PSI for the Fiero injectors (V6 only). Other injectors are probably different.

The components of the system are numbered in the photos. A test procedure and description of the numbered items are at the bottom of the page.

We make no attempt to explain all the small details here but would be happy to answer questions directed to fierosails@yahoo.com.

This project uses flammable liquids, electricity, and high pressure. The dangers are obvious. Use this information at your own risk.

Paul McKibben Norcross, GA

Copyright November 2006

This is a view of the entire setup.

A view of the fluid reservoir.

Closeup of the fuel rail.

Fuel rail support details.


Item 1 - An air compressor with a regulator. For the Fiero V6 injectors we reduced the output pressure to 40 PSI. The compressor could be any size that generates 40 PSI. The volume of air used is very low. See Item 3 for alternatives.

Item 2 - A fuel rail from the Fiero. This could be any fuel rail that will fit the injectors you are testing. We got ours from a salvage yard but there is no reason you can't use one off your car, then replace it when testing is complete.

Item 3 - A reservoir for test fluid (kerosene). This is made from 2" threaded pipe and caps. The caps were drilled for pipe fittings for fill and discharge ports. The pipe itself was drilled for an air inlet fitting. The reservoir is filled via the valve in the top, Item 9. It is possible to rig an automotive fuel pump inside a gallon jug to get pressurized fluid. If you do this you can eliminate the air compressor and reservoir.

Item 4 - A digital scale that reads in grams or tenths of an ounce. It is used to weigh the fluid in the collection jar to determine flow rate. The use of a graduated beaker would be better but we don't have one.

Item 5 - Kerosene. We got a gallon from Ace Hardware. It is the kind suitable for oil lamps. This type kerosene is not necessary but is what was available. Used kerosene is poured back into the jug.

Item 6 - Power cord with cigarette lighter adapter. This is the source of 12V power which is supplied to the injectors via the Power Switch, Item 10.

Item 7 - Tags with wire tie-wraps; used to identify each injector with information about the test. (I.e. - Injector #1, no leakage, narrow spray pattern, 96 gm/min flow rate) Useful because it is difficult to identify an injector after removal from the fuel rail.

Item 8 - Fuel filter. This is necessary to prevent bits of junk from clogging an injector. A clogged injector frequently requires discarding the injector.

Item 9 - Fill valve. A ball valve that has 1/4 turn to open .

Item 10 - Toggle switch that controls 12V power to the injector under test.

Item 11 - Plugs in the fuel rail ports for the Fuel Return line and Cold Injector line. (Don't recall the sizes.)

Item 12 - Rubber fuel line from fuel filter to fuel rail inlet.

Item 13 - Fuel injector electrical connector. Pulled from salvage yard.

Item 14 - Cigarette lighter power adapter. Or use alligator clips/devices to connect directly to a car battery. Beware of sparks around the kerosene.

Item 15 - One-inch diameter wood dowels mounted to the fuel rail. This allows the fuel rail to be lifted from its base to ease installation/removal of injectors. The base is drilled with 1" holes to accomodate the dowels. The picture shows the fuel rail lifted from the base and lying on its side.

We found all connectors, pipe, clamps, etc., at Ace Hardware.


Injectors are tested individually. After the test equipment is assembled, do the following:

1. Take precautions both to avoid fire and to suppress fire should it occur. As a minimum have a fire extinguisher handy. Keep the air compressor and power sources at a distance from the test setup.

2. Install all 6 injectors in the fuel rail and lock them into position.

3. With the air line to the reservoir disconnected, fill the reservoir with kerosene via the valve on top of the reservoir. Kerosene will run out the air inlet when the reservoir is full.

4. Close the fill valve. Attach the air supply line to the reservoir via the quick disconnect. (The quick disconnect fitting is essential for safety. Do not connect the air line to the reservoir without one.) The air line should be pressurized at this time. If not, it is possible for kerosene to drip into the air line and contaminate it for future use.

5. Observe if any of the injectors leak and record the results.

6. Plug the 12V power cord into an automobile cigarette lighter or other 12VDC source.

5. Make sure the power switch is off, then connect the injector plug to #1 injector.

7. Put a container below the #1 injector to catch the fluid. (A graduated beaker is best.) Apply 12V power to the injector for 60 seconds. Observe spray pattern during this period.

8. Measure the fluid in the container. If you don't have a graduated beaker you can weigh the fluid with an accurate scale that measures in grams or tenths of an ounce. Record all results including spray pattern.

9. Repeat the test process for all injectors and record the results. Refill the reservoir as required by removing the air line and filling from the top.