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6.2 won't start when warm

Discussion in '1982-Present GM Diesel' started by caliclunker, Feb 2, 2005.

  1. caliclunker

    caliclunker Registered Member

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    My beautiful blue and rust 83 Suburban 6.2 diesel won't start when warm. It will start fine if it's stone cold, and fine if it's fully warmed up, but if I stop and leave it for 20 minutes or so, the glow plugs don't come on and it won't start. If I sit and wait until the temp gauge gets down to about 100 the glow plugs finally kick in and then it fires right up. New glow plug controller, new glow plugs. It seems if I'm below about 150 on the temp gauge I have this problem. I'm new to diesels and am stumped. I suppose I could bypass the controller with a manual switch, but I'd like to figure out what's going on here. Any ideas?
     
  2. kennyw

    kennyw N9PHW Premium Member

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    If it is that warm it would not need glow plugs to start is the only reason they are not cycling on. The problem is most likely the injection pump solenoid getting weak. There are 3 positions on the injection pump. Full fuel (cold start mode), run (also warm start) and off. What is happening is the solenoid will go to full fuel to start it cold without problems, but when the motor is warm the solenoid is too weak to pull it out of the off position to the run position.
     
  3. caliclunker

    caliclunker Registered Member

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    thanks! you're worth the membership fee here already, if it works. I will check that out tomorrow. Is there a way to test that, short of just putting in a new part?
     
  4. BlueBlazer

    BlueBlazer 1/2 ton status

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    You say it starts fine if fully warmed up, shut off, then restarted? If so, I would not worry about the injector pump for now. You need to focus on getting the GPs to work.

    The fuel solenoid is only on and off from what I have seen. There is no difference in its operation from temp changes. It has a single wire going to it that does not change in power to change the position of the solenoid.

    To make sure it is not the solenoid, simply disconnect and reconnect the pink wire on the IP when you have the problem (with the ignition to on) and listen for a click.

    Good luck.
     
  5. caliclunker

    caliclunker Registered Member

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    yes that's right. Fully warmed up I can turn it off and then restart it. I'll check out that solenoid though. A question. At what temperature is the glow plug controller designed to activate the glow plugs? If I bypass the controller and send current to the glow plugs when this is happening and it starts right up I'd know it's not a fuel problem. How do I do that safely without frying anything? Thanks, and any other random advice or ideas appreciated.
     
  6. dieselponyexpress

    dieselponyexpress 1/2 ton status

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    I 2nd that.

    From your description I think it is the glow plug inhibit switch. The switch was designed to prevent glow cycles above 125°F engine temp.
    If equiped with the switch, it should be wired between GP controller (@ driver's side cyl head) and GP relay (@ firewall).

    For testing purposes you could just bypass it.

    Not sure if your burb did come with the switch though. If memory serves me right, only for 1984 GM decided to use it.

    Regards,
    Walter
     
  7. kennyw

    kennyw N9PHW Premium Member

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    Oops, I mis read his first post. Thought he said it didnt start when warm :doah:
     
  8. caliclunker

    caliclunker Registered Member

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    Thanks for all your help...I thought some of you might be curious....the solution to this problem remains elusive. the fuel solenoid is OK, there doesn't seem to be a glow plug inhibit switch. I let you all know if I ever figure it out.
     
  9. 6.2Blazer

    6.2Blazer 1/2 ton status

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    I had problems with the temperature sensor that controls the GPs in the past.........this is the one that is mounted on the front of the engine, kinda' torwards the passenger side, and is NOT the one that controls the temp. gauge in the cab (at least this is the way my '90 is setup). The temp sensor was not letting the GP's activate because of the temp. inhibit feature (the bad signal was apparently saying the engine was warm). If I remember correctly you can simply unplug the temp. sensor and the default signal is basically for a cold temp. and will activate the GP's.

    With that said, I would think the engine would start even without the GPs if it was at full temperature and only sat for 20 minutes......even if it was very cold outside.
     
  10. kennyw

    kennyw N9PHW Premium Member

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    I'd agree with that... I have fully manual glow plugs and dont have to use them unless I let it sit for more than 2 hours. Even then it only takes 4-5 seconds to warm up the plugs enough to start it on cold (30-40 degree) days.
     
  11. caliclunker

    caliclunker Registered Member

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    hmmm... that gets us back to your first idea about the injection pump solenoid. Or a fuel problem of some sort. I did do the simple test blueblazer62 suggested, to see if I could get a click from that solenoid, which I could. I'll play around with the beast tomorrow or Saturday and see if I can pin it down. I'll either come back here with the story of the cure, or more data so we can figure this out. I really appreciate everybody's help.

    This did start happening about the same time I had the radiator replaced, if that's a clue.

    :confused:
     
  12. dieselponyexpress

    dieselponyexpress 1/2 ton status

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    In your first post you mentioned the glow plugs not coming on when sitting for a short time. On the other hand, glow plugs do well with a cold engine.

    An inoperative ip solenoid don't cause these symptoms.

    Edit: Sometimes an aftermarket controller is the problem. Try the AC Delco unit.

    Regards,
    Walter
     
    Last edited: Feb 13, 2005
  13. caliclunker

    caliclunker Registered Member

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    End of the Story

    Thought I'd tell you all what happened. I put in a manual switch for the glow plugs and if I turn them on, it starts right up. I got a very thorough email directly from a very knowledgeable and seasoned diesel mechanic who couldn't post here, that explained what is happening.
    The short highly condensed and edited retelling is that (1) the original glow plug/controller set up had its shortcomings anyway, and (2) the fuel injection pump if somewhat worn does get enough weaker in a warm condition at engine cranking speeds to make the engine hard to start. Increase the cranking speed, repair the pump, or fire up the glow plugs will all overcome this problem.
     
  14. kennyw

    kennyw N9PHW Premium Member

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    I think we should all chip in and buy that guy a membership... He's probably been helping out a few of us here via email (and I think I know who you are talking about). :thumb:

    I've got $10 in Paypal right now... anyone want to chip in?
     

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