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  1. #1

    Default 99 K2500 7.4 Won't start when it's above 40F outside

    t started acting up last fall by really driving crappy but I had to ignore that at the time and we weren't driving it very much. Then this horrible winter came and we didn't dare to take it into the shop to disappear for a while.

    Well things got worse because now it starts right up when it's cold just fine. It still runs like crap but it was enough this winter for the occasional use. But once it's above 40F (approx) it won't start at all.
    It makes a bit of an initial start and then nothing. You can smell lots of gas at the tailpipe.

    My initial thought is that it's overly rich which would be consistent with the cold weather performance. It really does run better when it's really cold, say 15F. But perhaps it's just the opposite and it's too lean?

    There's no check engine light during any of this.
    The air and water temps are accurate and normal via the OBDII access.
    No registered codes.

    When it was still running a few months ago the FP was normal even though the car ran poorly.
    Now with just the Ignition on the FP via OBDII is zero.
    I haven't tried measuring directly again with a FP gauge as yet.

    I suspect some sensor(s) is faulty. I need to get the car moving again so that the general poor running issue can be addressed at a repair shop.

    Fuel pressure is normal and there's a brand new filter in it. We also used a couple cans of Techron in it as well water remover.

    Other than towing it there can anyone suggest which things to check?

    Any pointers are most appreciated

    Thanks.

    Bob S.

  2. #2

    Default

    By chance have you tried a very small touch of ether? (to rule out electrical ignition issues)

    I know it's not a mechanics best choice, but it can help diagnose the issues.
    2010 Silverado LT 1500 5.3L 4X4
    '95 BMW K1100LT
    '97 BMW K1100LT

  3. #3

    Default

    Does the fuel system hold pressure when the pump is off? It does kind of sound like it is getting too much. Fuel injectors stuck open would allow too much fuel, and would show up as a fuel system that can't hold pressure. I would probably also pull the vacuum line to the fuel pressure regulator to see if there is gasoline in that vacuum line. Sometimes the diaphragm in the regulator develops a leak that allows excess fuel into the intake.
    '98 K1500 Suburban LS 5.7 L 4L60E NV246 ARB
    '92 Ford Explorer XLT 4x4 4.0 L A4LD BW13-54 Trac-loc rear
    "My toys were the greasy cogs and springs and pistons that lay around all over the place, and these, I can promise you, were far more fun to play with than most of the plastic rubbish children are given nowadays." Danny in Roald Dahl's Danny The Champion of the World

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  5. #4

    Default

    Thanks for the replies.

    No ether but I have to say that this issue with not being able to start at all is like clockwork according to the outside temperature.
    There's nothing random or irregular about it.

    We had mostly very cold weather this winter but at times when it got above approximately 40F it just would not start or even begin to catch at all. As soon as the temperature dropped it would fire right up.

    I will try and see today with the ignition on if it develops fuel pressure and how long before that drops off.
    I'll monitor the voltage as well.

    I'll try to locate the FP regulator as well.

    I don't have a service manual for this car.

    Is there an on-line version available somewhere?

    Thanks again

  6. #5

    Default

    Autozone has a version of the Chilton's DIY manuals on their site if you are willing to register with them for free.

    You might check with your local public library -- many public libraries have online subscriptions to auto repair manuals available for their patrons.

  7. #6

    Default

    Well let's try this on for an idea.

    I hooked up my FP gauge and just turned the ignition on.
    It ran up to 50 psi and then immediately began to fall off with the key still on.
    After about 10-15 seconds it was down to 30 and still falling.

    So I thought hmm, an injector(s) is leaking?
    Ten I tried starting it and it fired right up! I'm very surprised since it hasn't been starting for several weeks now and it's no colder today than it has been.

    But perhaps it is the injectors and when their cold or just sometimes by happen stance they don't leak as much.

    I let the engine run for a while and then turned it off.

    It slowly dropped FP to 35 psi and then stopped. After 10 minutes it was at 29.

    Now I've started it again. Fired right up. I then shut it off and it's going down but very slowly.

    So if the the injects then perhaps the regulator or the pump?

    How long should it hold the FP @ 50?


    Once again, when I first put the key on today it went up to 50 and then quickly started dropping off to 30.

    EDIT: OK I just discovered that the FP gauge connector was missing it's little tubular rubber seal and so there was slight weepage at the connector. So that may account for this leakdown of pressure.
    Fixed the seal and now I'm repeating all this.

    I can't locate the FP regulator. Is it buried some place special?
    The parts diagrams are of much help on this.

    Quote Originally Posted by MrShorty View Post
    Does the fuel system hold pressure when the pump is off? It does kind of sound like it is getting too much. Fuel injectors stuck open would allow too much fuel, and would show up as a fuel system that can't hold pressure. I would probably also pull the vacuum line to the fuel pressure regulator to see if there is gasoline in that vacuum line. Sometimes the diaphragm in the regulator develops a leak that allows excess fuel into the intake.
    Last edited by staatsof; 04-07-2014 at 11:37 AM.

  8. #7

    Default

    On the 5.7's like mine, the fuel pressure regulator (fpr) is inside the intake manifold. My impression has been that, on the 7.4, the regulator is attached to the fuel rail. According to my Hayne's manual, the fuel rail is kind of underneath or alongside the lower intake manifold. It will have the fuel lines attached to it and the fuel injectors and the fuel pressure regulator.

    I do not know if I have seen an official "bleed down" spec from GM. Ford's spec for my Explorer was something like no more than 3 psi in 10 minutes. In practice, it would usually hold pressure for a long time when it was working correctly. If you fix the leak around the fuel pressure test port and can still visibly see the pressure drop, then it is probably "out of spec."

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  10. #8

    Default

    It takes a very long time to bleed down now that I fixed the test port leak, sigh ... I thought I had something there.

    Don't know why it starts today except that it's damp and raining and feels colder.

  11. #9

    Default

    Intermittents can be very frustrating. My advice at this point is to be sure to keep all your diagnostic stuff handy. Next time it won't start, put the fuel pressure gauge on it and see if the fuel pressure is up to spec when it refuses to start.

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