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Well it's not the injection pump... Any opinions?

Discussion in '1982-Present GM Diesel' started by imiceman44, Mar 8, 2004.

  1. imiceman44

    imiceman44 1 ton status

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    Well it\'s not the injection pump... Any opinions?

    I just bought this TD burb as some of you know and it had some kind of problem, thought it was the injection pump or the lift pump.
    I decided to do simple checks first before dumping any money.
    Did a compression test on the driver side bank which is easier due to turbo stuff on the passenger side:

    first cylinder: 260PSI
    I thought that alittle low, lets see the rest




    second was 260PSI so I think well at least consistency,







    The third one came out at 200PSI, nwo I am thinking OH F...





    Check the fourth and it's 190PSI.

    I guess I am going to put another engine.
    I have a couple of 6.2's waiting, I will check the compression on them and if it's good then I will dress one up and then install it in the Burb.
    What do you guys think a min pressure I should bother to work with?
    Would I want at least 300PSI to bother working on them or would a consistant 280+ work for me.

    I will probably be doing the testing this coming week end, and if I find a good block I will rebuild an injection pump, injectors , get some G60's and a new lift pump, install the Turbo setup and voila a good combo.
    /forums/images/graemlins/peace.gif

    Hey Arvetek

    Do you think the low compression with probably an injection pump that's on it's way out would make it not start?
    I never saw it runnig so I only could go on what they told me and what i tested so far.
    I want to send the pump out for a rebuild and maybe they can tell me how bad it was.
     
  2. ZZ4x4

    ZZ4x4 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    Try swapping the injector from the 260psi cylinder into the 190psi cyl and see if the compression increases. If you have an open injector failure , you will both pump air into the fuel line causing knocking and hard starting, and low compression. That was my experience on an M1008 I had. Fixed everything with a couple $24 injectors. I saw it first by slightly cracking each fuel line by the injector. Bubbles came from the fitting at bad injectors, while just fuel seep came from good ones. Good luck
     
  3. imiceman44

    imiceman44 1 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    [ QUOTE ]
    Try swapping the injector from the 260psi cylinder into the 190psi cyl and see if the compression increases. If you have an open injector failure , you will both pump air into the fuel line causing knocking and hard starting, and low compression. That was my experience on an M1008 I had. Fixed everything with a couple $24 injectors. I saw it first by slightly cracking each fuel line by the injector. Bubbles came from the fitting at bad injectors, while just fuel seep came from good ones. Good luck

    [/ QUOTE ]

    Are you saying that when I crank it over to test compression, the injectors could leak back into the fuel system?
    I should probably check that.
    Thanks
    /forums/images/graemlins/thumb.gif
     
  4. arveetek

    arveetek 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    Have you checked the other bank of cylinders yet? I'm curious what compression they're showing.

    How many 'puffs' did you try to get those readings?

    I think 300 psi is generally regarded as the minimum compression needed to run well, while one used 6.2L supplier I know won't sell an engine without at least 350 psi on all cylinders.

    Definitely low compression coupled with a weak IP could cause a no start scenario.

    Casey
     
  5. BlueBlazer

    BlueBlazer 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    Have you seen how small an injector orifice is? There is no way you could lose any more than a negligible amount of compression from losses into the injector itself.
     
  6. BlueBlazer

    BlueBlazer 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    Sounds like a rebuild might be needed. Did you squirt oil into the cylinders and retest to see if its rings? Is your cranking speed where it needs to be?
     
  7. arveetek

    arveetek 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    Do NOT squirt oil into the cylinders on a diesel to test the compression. While this is an acceptable practice to use on a gasser, they don't call these diesels "oil burners" for no reason. And while it's very unlikely that the oil could be ignited on a cold engine, it's still possible. This could cause personal injury and/or ruin your testing equipment and/or cause engine damage.

    Casey
     
  8. Diesel Dan

    Diesel Dan 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    I had a 6.2 with ~300psi on all 8 cylinders. Ran good when warm, started very poor when cold. To start half way decent it had to be plugged in at anything less than 35*F. Even then it still smoked. Dropped in a remain from Avant salvage using same injectors/pump and it fires up WAY better now.
     
  9. BlueBlazer

    BlueBlazer 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    I very seriously doubt that you could ever ignite lube oil in liquid form in a small amount in any diesel. First of all, if you are testing compression and find the reading to be low, its likely the engine can barely fire on diesel, so do you honestly think a little oil in the cylinders is going to magically combust? Has this ever happened to you? The only thing I would be a little hesitant about would be hydrolocking it, but if you use some common sense and use a very small amount of oil just to fill the ring gap then that shouldnt be a problem. Best thing to do is a leakdown test after you find a cylinder with low compression.

    Edit: Although the possibility of it happening is so remote its not even funny, I will say that even the chance that it might happen might be enough to make it not worth doing, so after thinking about it I kind of agree with you now.
     
  10. ZZ4x4

    ZZ4x4 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    I don't know if you'd lose enough compression through a bad injector during cranking to show up. Guess it depends how messed up the injector is. I know swapping an injector is easy and would try it before I worry about rebuilding or scrapping a motor over a compression issue. I also know that in a running engine you can blow plenty of air back into the fuel line through a bad injector. Just an easy check to eliminate a possibility. /forums/images/graemlins/wink.gif
     
  11. imiceman44

    imiceman44 1 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    [ QUOTE ]
    I had a 6.2 with ~300psi on all 8 cylinders. Ran good when warm, started very poor when cold. To start half way decent it had to be plugged in at anything less than 35*F. Even then it still smoked. Dropped in a remain from Avant salvage using same injectors/pump and it fires up WAY better now.

    [/ QUOTE ]

    OK finally lots of responses. /forums/images/graemlins/thumb.gif
    Well to start, the temp was 80 deg.
    Speed was great, new batteries and new starter.
    It took about 12-15 pumps to reach the numbers I got and the last 2-3 didn't add anything
    I didn't try the other side yet, and didn't try oil in the cylinder because no matter what the problem is, if there is a problem other than the injectors or the pump, I want to replace it, and check it later.
    I have 2 engines laying around so i will be pulling this one out and do more testing where it's easy on a stand without the heater, Turbo, and all the other junk around it.
    I guess I will not use an engine with less than 330+, since I have them, and if they are no good I will not Buy anything with less than 350PSI.
    I will give you an update when I have one.
    Thanks again guys.
    /forums/images/graemlins/thumb.gif
     
  12. u2slow

    u2slow 1/2 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    If you get to the point where the heads have to come off for any reason... have them magnafluxed!

    Cracked heads are fairly common. Usually radiating from the valve seats. Compression leaks into the oiling passages so there's no real obvious sign. I've heard of a fix that involves sleeving the passage with a valve guide... /forums/images/graemlins/eek.gif ...and it apparently works /forums/images/graemlins/yikes.gif
     
  13. imiceman44

    imiceman44 1 ton status

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    Re: Well it\'s not the injection pump... Any opinions?

    [ QUOTE ]
    If you get to the point where the heads have to come off for any reason... have them magnafluxed!

    Cracked heads are fairly common. Usually radiating from the valve seats. Compression leaks into the oiling passages so there's no real obvious sign. I've heard of a fix that involves sleeving the passage with a valve guide... /forums/images/graemlins/eek.gif ...and it apparently works /forums/images/graemlins/yikes.gif

    [/ QUOTE ]

    When I get to the point I am getting the heads off, I have 6.5 heads coming my way that I will be using so i will not Magnaflux my 6.2 heads.
    /forums/images/graemlins/peace.gif
     

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