how do you know if fuel injector is bad?

I have a 94 grand am 3.1 and the check engine light comes on after driving on the highway for about 45 min. I've been told by a couple people I have a bad injector. I've ran a diagnostics and don't get any codes.

5 Answers

  • 1 decade ago
    Favorite Answer

    You can try pulling the sensors of each injector while the car is running to see if there's a difference in how the car runs.

    Pull off the sensor wire to an injector and if the engine starts running rougher, that injector is good. Plug it back in and repeat that for each injector. If you pull the plug off of one and there's no change in engine performance, it's probably bad.

    But, I don't think your light would come on that late if you had a bad injector. You would notice the light immediately.

    You would also notice that your car is running like crap.

    If there's a light, then there's a code. You're doing something wrong when you're running the diagnostics.

    Recheck the directions to the computer you have. Your computer might not have an updated program or a complete program that a dealer's might. So, I'd take it to a dealer. They should be able to find the problem easy enough.

  • 1 decade ago

    If your mil is lighting up, you should have a code. you can check injectors with a volt/ohm meter, pull the harness connector off each injector, set meter to ohms, and touch probes to injector contacts, it should give a reading(you need to check manufacture specs for proper value, although a reading less than infinite INDICATES it is probably good. In addition, using an analog meter, have an assistant crank engine over a few times while touching the harness contacts with meter probes,(meter should be set to 12, or 20 volt,D.C. scale) needle should fluctuate if injectors are getting voltage from computer. Repeat this procedure at each injector. IT IS IMPORTANT TO PULL THE FUEL PUMP FUSE, AND/OR THE FUEL PUMP RELAY FUSE BEFORE ATTEMPTING EITHER OF THESE TESTS! This is to ensure that the fuel system is disabled! Well, I hope this is a help, Good luck!

    Source(s): Dunn-Wright Transmission Service and Auto Repair. owner-(burts chevy)
  • 1 decade ago

    You might just have a leaky radiator, and your engine is overheating after 45min of drive. Doubt if it is a bad injector. You would have seen a huge drop in performance.

    How did you run the diagnostics?

  • 1 decade ago

    how did you run diagnostics? if you truly ran diagnostics,the proper way with proper equipment, and it showed no failure codes, then you have a bad ecm. one of the ecm's jobs is to remember why it throws the chk eng mil on; if it cant remember, then it is bad. plain and simple, end of story. you have to start there. i get this funny feeling diagnostics were not run correctly 1st. go to a shop, get a 2nd opinion. ecm failures, although rare, do happen, but to diag a car properly, you look at the ecm last as a potential failed part.

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  • Anonymous
    1 decade ago

    take a long screwdriver and put 1 end on each injector and the other end to your ear,and listen for a rattle noise,to hear that the injector is might sound silly,but it works.

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