What are the symptoms of a bad CIS injector?

[MJM911SC]

I just did a search on CIS fuel injectors and still have these questions.

What are the symptoms of a bad CIS fuel injector?

Please describe your DIY set up for testing the injectors.

Is it acceptable to change only the bad injector or do they have to all be changed together?

Thanks in advance,
Mike M
Davis, CA

[Jim Sims]

Paraphrased from Watson's "How to Tune and Modify Bosch Fuel Injection".

Symptoms of bad injectors:
poor gas mileage
poor power
erratic engine operation
hard starting

Tests:

No smoking or open flames, do this outside with ventilation, not in a garage with a hot water heater pilot light. Have a gasoline fire rated fire extinguisher on hand. Safety goggles are also recommended in case one gets sprayed in the face with gasoline.

Spray pattern: remove injectors from intake leaving the fuel lines attached. Place injectors in a fuel safe container, (not glass) metal is best. Jumper the fuel pump relay so the fuel pump runs. Lift the airflow sensor plate (under air filter) all the way up and allow the injectors to fully flow. Close sensor plate and wait for about three seconds and then raise the plate between an 1/8" and 1/4". Look at the injector spray patterns, straight on narrow cone shaped pattern is correct, a cone spraying off to side is acceptable, a stream pattern is bad and means the injector should be cleaned or replaced.

Leaking injectors: remove injectors from the intake leaving fuel lines attached. Jumper the fuel pump relay so the fuel pump runs. Check the injectors for leaking. Raise the airflow sensor plate; the injectors should spray. Close the plate; the injectors should stop spraying right away. If the injectors are leaking try purging them of debris by allowing them to spray at full volume for 10 seconds. Repeat leakage test. If an injector(s) continues to leak replace it.

Unequal flow check: remove injectors from intake leaving fuel lines attached and place each in its own container. Jumper the fuel pump relay so the fuel pump runs. Raise the airflow sensor plate 1/4" and hold there for thirty seconds. Fuel volume delivered to each container should be the same within 10%. If this test is passed then repeat holding the plate at 1/2 way open position for 30 seconds; again the fuel volume delivered to each container should be within 10%. Fuel volume can be measured with a graduated cylinder or a glass measuring cup with millilter markings. Unequal fuel delivery can sometimes be fixed (as can an irregular spray pattern) by having the injectors ultrasonically cleaned. If cleaning fails the injectors should be replaced.

A single bad injector may be replaced provided it gives matched fuel delivery volume as tested above.

Sometimes the CIS injectors are hard to remove from the intake manifold. I made a removal tool from a flat steel prybar (trade name "Superbar") obtained at a local hardware store. I used a die grinder with a stone (a rat tail fille would work too) to open up the nail pulling notch to match the neck of the fuel injector. I put a thin bit of wood under the fulcrum of the pry bar to protect the engine and gently pryed out the injectors. One might also want to consider replacing the rubber injector seals at this time. Cheers, Jim

[IROC]

I had a CIS fuel injector become clogged (or at least the flow pattern was disrupted enough to prevent proper combustion) and the engine ran very poorly - reduction in power, idled terribly but ran *decent* at higher rpms (4k+) and it sounded horrible. Almost sounded like a VW engine at idle.

I was at a track event and one of the technical gurus that was there diagnosed it as a clogged injector and I poured a full bottle of Techron into about 8 gallons or fuel and after about 20 miles, it cleared up.

I ended up replacing all 6 injectors. If they have any age at all on them, I would replace all 6. They're cheap (by modern fuel injector standards) and not that hard to replace.

Mike