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Thread: 99 GMC Sierra Z71 5300 eng.

  1. #1
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    99 GMC Sierra Z71 5300 eng.

    Hello everyone! I'm new to this forum and was hoping someone could help me. I recently purchased this truck after selling my Dodge/Cummins. I noticed sometimes when I turn the ignition on, there's a noise that I would assume is the fuel pump building pressure. Then, when I turn over the engine, it fires right up. But then after I shut it off and go back to start it later, the noise is not present and the engine just cranks without firing unless I push the gas pedal to the floor and then it starts. Almost like the fuel system loses its' prime.

    Does anyone have any ideas? By the way, there are no trouble codes present.

    Thanks in advance for your help.
    '99 GMC Sierra 1500, Z71, 5.3L

  2. #2
    Senior Member FaselZ71's Avatar
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    Well you fuel filter could be clogging up and your fuel pump senses the line is pressurized and once you push gas it releases the pressure and kicks on maybe. Someone else smarter then me will post soon but hey Welcome to the forum! We have cookies!!! j/k

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    Welcome to the site;

    I have had this problem with both the 5.3 and the 6.0L engines.
    The problem on one was that the fuel pressure was too high, and the fuel pressure stuck the pintles in some of the injectors. These stuck pintles permited the fuel to run into the cylinder and basically flooded the engine. Not enough to hydraulic it, but enough to make it difficult to start.
    The next engine just had dirty injectors, and they would not seal. This too allowed the fuel to flood the engine, and also created a difficult start.

    Both of these engines had the same things in common. Each would cold start perfectly, since the fuel would evaporate out of the cylinders permitting a perfect fire in the cylinder.
    Again both would not fire when the engine was run and allowed to sit for a few minutes. These few minutes allowed enough fuel to leak in to the cylinders to create a difficult start.
    Both would start almost immediately after the engine was shut off.
    Both smelled of raw fuel in the exhaust after a difficult start.

    I believe that somehow the injectors are leaking into the cylinders and creating a difficult start.

  4. #4
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    Thanks for the welcome and advice.

    75K30, I think you hit it on the head. It will cold start no problem but after it has been run is when it doesn't like to start. To me it seemed like it didn't have fuel to fire on until I stepped on the gas.

    I'm accustomed to a diesel where you turn the ignition on and wait for the "wait to start light" to go off before cranking. During this time, you could hear the fuel transfer pump working to provide fuel pressure to the injection pump.

    During cold starts, I hear what I think is a fuel pump pressurizing before starting. But, when its warm, I dont hear it and I know that I'll have to put the gas pedal to the floor to start. So I was thinking a bad temp sensor sending telling the fuel pump not to pump. But there again, no codes.

    I have put a couple of bottles of injector cleaner through it to no avail. Are the injectors serviceable in these trucks or are they designed to be thrown away and replaced?
    '99 GMC Sierra 1500, Z71, 5.3L

  5. #5
    Full Member bjones's Avatar
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    Injectors on the Vortec 5300 are similar to the ones found in an LS1, a Bosch style, if I'm not mistaken...

    Saying that you could take them out and service them, or you could go ahead and replace them, I don't know what you'd want to do...

    My Vortec 5700 has that accursed spider CSFI system. Non upgradeable, non serviceable. >:Z

  6. #6
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    I failed to notice the year of your ride, and suggested that a pintle might be stuck, but your injectors do not use these, and I want to be as accurate as possible.
    Still the same symptoms apply, and this does nat make a bunch of difference.
    Regular bottle type injector cleaner is and should be used as a preventative cleaner, and not as a fix after the fact. These are not concentrated enough to do a satisfactory job.
    The easiest route is to clean the injectors in place because you do not have to remove the injectors (which can be a real chore on some import engines). Running cleaner through the injectors while the engine is running also removes many of the deposits on the valves and inside the combustion chambers. This eliminates the need for an extra cleaning step if the engine is full of carbon deposits. The job takes only 10 to 15 minutes, and you can usually tell right away if the treatment addressed the problem (engine runs smoother, idle misfire gone, etc.).
    When doing the cleaning procedure itself, you must use pressurized equipment to feed the solvent directly into the fuel rail while the engine is running. This means you either have to disable the fuel pump and plug the fuel return line, or install a U-tube so the fuel will recirculate right back to the tank. Disabling the fuel pump can set a fault code on some cars, requiring you to clear the code after the job is done.
    Easy as it is, there are some limitations with on-car injector cleaning. One is that badly clogged injectors may not pass enough solvent during a normal cleaning cycle to be thoroughly cleaned. Some baked-on deposits can be very difficult to remove, requiring you to prolong or repeat the cleaning process. And if on-car cleaning does not work? You will have to remove the injectors and have them cleaned on an injector cleaning machine - or replace them.
    Another limitation with on-car injector cleaning is that you may have to do some additional tests to confirm that the injectors responded well enough to your cleaning efforts. A test drive may be needed to see if the driveability symptoms have been eliminated, or you may have to check emissions to make sure HC and CO levels are back to normal. A power balance test is another way to confirm engine performance and check for weak cylinders (there should be less than a 10% power variation between cylinders). An injector pressure drop test will tell you if the injectors are flowing evenly or not.
    This is a bunch of info to take in all at once, but you do not want to replace your injectors, These are pretty spendy, and will cost you a fortune.
    These injectors are actually pretty easy to remove should you chose to take them in for a cleaning, but expect to pay around 25 to 35 bucks per injector for this service.
    Try to clean the injectors while they are still in the vehicle, and I do believe your problem will go away.
    Then you can use your cans or bottles of cleaner to help maintain a clean set of injectors.
    Much luck to you!

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    75K30, thanks for the updated info. I've never heard of an injector cleaner attaching to the fuel rails and cleaning the injectors in the engine. Can you point me in a direction as to what vendors make and sell the set up that you're referring to?

    I still think that it may be something related to the fuel pump. During cold starts, I hear what I think is the fuel pump building pressure right before I crank the engine over. Engine starts effortlessly.

    However, after I shut it off and go to start again when warm, I don't hear the fuel pump (what I think is the pump) and that is when the truck will not start unless I step on the gas pedal while I'm cranking.

    I'm thinking a sensor or device that measures temperature and communicates data regarding fuel pressure.
    '99 GMC Sierra 1500, Z71, 5.3L

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