How to check for bad injectors

WOODY1000

MEMBER
CHEVROLET

I have a 1991 chevy beretta, 3.1 engine and 87,000 mile, a reply to my prvious post was helpfull, thank you, To check for a bad injector, is that something a shade tree guy like me can do or does a garage need to do it, also if the problem comes out to be a bad head gasket, is it worth replacing or is the motor junk~?

1 Reply

MIKEYBDMAN

MECHANIC
623 POSTS

There is a fuel injector balance test that you may be able to do. You will need to either make a tester, or come up with a way to power the injectors. Look at this web site and read how they made a 12 volt tester, but you can instead use the 5 volt wires and make a 5 volt tester. If you go to the trouble, I would make it a 12 or 5 volt tester. Of course depending on your elictrical ability, you can wire up test ports to check your voltage drop across each injector.
Ok, here is the instructions of the balance test. See if you think you can perform it.

Connect fuel pressure gauge inline of the fuel rail. You must bleed the fuel gauge to ensure a correct reading. Turn ignition switch on, and read pressure when it stabalizes. Write down that pressure. Then with your 5 volt tester, supply power to the no.1 injector. Read what the pressure drops to with the injector powered. Do not hold power on for more than 5 seconds. Then repeat the steps to test all 6 injectors. Compare the pressure drop to each other. If any one or two injectors read more than a few psi high or low, then suspect them for being bad. As little as a 1.5 psi to high or to low will indicate a faulty injector.
It was thought before that just checking the resistance of each injector was a good test. But now the pressure test is a better way, and the voltage drop test across the injectors is the best way to indicate a bad injector.
I am going to cut and paste the test equipment GM uses. Get a hold of one of these testers, and you are set. They sell for hundereds of dollars.

Kent-Moore Fuel Injector Tester, tool J-39021, has the capability of performing injector balance and coil tests on all GM and many non-GM fuel injection systems. In addition to the familiar fuel pressure drop test, the injector coil test is a new test whereby the injector's resistance is measured during normal operation by feeding a fixed current through the injector and measuring the voltage drop across the injector. Injector coil failures are more accurately detected using this method than by simply measuring the injector's resistance with an ohmmeter. Refer to the instructions included with the tool.

For further information, refer to TSB 93-6E-14, dated June 1993. (Corp. Ref. No: 316501R)

NOTE: Measuring injector resistance is not a fool-proof method of determining the condition of the injectors. A Fuel Injector Balance Test will more accurately determine the mechanical condition of the injector, while the injector resistance will determine the electrical condition of the injector.