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How to test lift pump and injector pump??

Discussion in '1982-Present GM Diesel' started by ringer, May 29, 2004.

  1. ringer

    ringer Registered Member

    May 26, 2004
    Likes Received:
    I have a post a fewe lines down describing my problem, but in a nutshell here it is:

    1985 Chevy Suburban 3/4 ton 4x4 6.2L diesel "J" code.

    I am experiencing what appears to be a "missfire" on one of my cylinders. Occaisional small amount of black smoke at idle. I have a few questions on troubleshooting my problem.

    1. I disconnected the air purge on the fuel filter and get a good flow of diesel when cranking.. Does this rule out the lift pump as the culprit because I get fuel??

    2. How do I test the injector pump? I see the two scribes on the block and the pump and they are aligned. Am I clear in my understanding that I can loosen the pump and rotate clockwise in small increments to determine ifr it is working?? What exactly am I looking for if this is the correct procedure?

    How can I test the individual injectors? I had not noticed earlier but SOMETIMES I get a small amount of black smoke at idle. Could this be due to a bad injector?? How do I determine if one is working??
  2. imiceman44

    imiceman44 1 ton status

    Aug 5, 2002
    Likes Received:
    Sacramento, CA
    I still don't know how you can test your injectors on the truck, if there is one I like to learn about it too, but usually I take them off (not very easy task) and take them to a shop for testing, there is a shop here that tests them for free. /forums/images/graemlins/thumb.gif
    As for the black smoke and shuddering, it could be an injector poping at a low pressure and dumping fuel too much.
    That could make the black smoke as black smoke is too much fuel for the Oxygen on a hot motor.

    For the injection pump, when you turn it it will advance the timing not test the pump.You can probably gain a little power by advancing it 1/4" or less, 1/8".

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