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Help! Must Crank Twice to start!

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by Rogue909, Nov 22, 2011.

  1. Rogue909

    Rogue909 New Member

    So my dad just purchased a used 2005 suburban (our last one was an 02 that we ran into the ground) and got a good deal on it...
    As with all good deals it has its qwirks, but my dad and I are handy with a wrench (OK not perfect, but on a scale of 1-10 id rate us pretty good at figuring stuff out and getting things fixed) so we figured sure why not, its a suburban, they are tough, the person we bought it from was less then mechanically inclined so its probably something stupid. Besides, we got a deal on it (even if we lose some money on repairs we still end up ahead.)
    Ok, dead end now.
    Heres what happens... when you crank the truck it cranks strong, but you sit there and crank it and it never fires... until you let go and drop the key back to the run position then crank again. Then it fires like a champ.
    First thought was the fuel pump, so we primed it (put key in run and wait....) then cranked, same story.
    So we drove it around for a bit (150 miles) hoping to trigger a code pop, nothing.
    Took it to a friends dad (a retired mechanic, he has a knack for motors) who told me it must be a sensor issue (his first guess was the crankshaft position sensor), replaced that and no dice. Same story.
    Took it to a local shop, had them scan it with one of their super scanners, nothing popped up on the scanners as being irregular.
    Gut feeling got the better of me so I picked up a fuel pressure gauge and tried that, now I got some weird numbers....
    When you first put the gauge on it reads 0 (car is off).
    When the car is switched to run it reads 0. (if im correct it should have pressure here)
    When you start cranking the gauge will slowly start going up, if you let it raise all the way to 45-50 it will fire and start running like a champ.
    If you stop cranking early (IE when the gauge is at 25~) then drop it to run and crank it again, fires right away.
    Once the truck is running, solid 60psi the whole time its running (havnt driven it with gauge on, the gauge we got has a short hose (dumb selection in hindsight) so the hood has to stay open while you ahve the gauge).
    When you kill the truck the gauge rapidly drops down to about 9psi (in approx 3 sec)
    From there the gauge will slowly drop to 0 (takes about 30-45 sec)
    If you attempt to start the truck while the gauge is dropping, it starts fine. If you let it hit 0 psi, start cranking.
    It should be noted that once the truck is running it has no problems, instant acceleration (for a suburban anyway), smooth idling, etc. I drove it to class and ran errands yesterday (150 - 200 miles) without any problems.
    I checked fuel pump relay, it looked alright, was a little brown on one side, went ahead and replaced it, no dice.
    Ran Chevron fuel cleaner through, no change.

    Now im confoundled. What would cause those symptoms?
    My first thought would be a leaking fuel check valve, but the system depressurizes so fast, and even when its in run it should be priming right?
    So then I thought maybe the fuel pump? But then it would show up during drives.
    Regulator? The pressure stays a solid 60 once its started.
    Line/Fuel Injector? MPG is too high to be "wasting" gas... 17.9 mpg (city65/hwy35)

    Maybe its not a fuel issue at all? Friends dad swears its got nothing to do with fuel and its a sensor (I would think the scans would pop something there)

    Some specs;
    2005 Suburban
    Z71
    4x4
    5.3
    FlexFuel
    110k miles

    Anyone have any thoughts? Im desperate here >.<
  2. McMahan

    McMahan New Member 100 Posts

    Wow that's very weird and never heard of this. I am a little stumped as well by what you wrote. To me it sounds like the fuel pump isnt sending enough fuel to the injectors as fast as it should thats why its taking long to start and another indicator to me is its loosing PSI real fast so that tells me the fuel pump isnt keeping the system primed. Personally I would just replace the fuel pump just out on general purpose and for peace of mind that if it doesnt fix it then that variable is out. Best of luck to you

    Also check the injectors and fuel rails and fuel press regulator
  3. Naptime

    Naptime New Member 100 Posts

    Fuel pump, change the filter too.
  4. Augie

    Augie New Member

    I'll be following this one.
    My 6.0 Denali XL is doing the same thing. No other issues, exept for the crancking.
    Let us know if you replace the fuel pump and if that fixes it for you. I believe it may be my fuel pump making it do that too.

    Thx,
    Augie
  5. MrShorty

    MrShorty Moderator Staff Member 1000 Posts 100 Posts

    Disclaimer: I'm assuming your '05 uses a continuously circulating fuel system like my '98 does. I don't know the newer GMs well enough to know if GM came up with a different (probably returnless) fuel system design.

    I mean no disrespect to your friend's dad, but when you put a fuel pressure gauge on it and you can see that the fuel pressure is that far below spec, that defines a fuel issue.
    Not necessarily. KOEO (Key On Engine Off), the fuel pump will only run for a second or two to build up pressure. If you don't immediately start the engine, the pump will turn off and wait for you to start the engine.

    As you've noted, the usual first suspect in a problem like this a faulty check valve. Other possibilities include just about any other fuel system leakage like a leaky injector or a leaking regulator.

    A couple of further tests I would suggest:

    If your '05 is wired like my '98, you can apply power to a lead that will feed power straight to the fuel pump and see how long it would take for the system to build up pressure.
    Turn the key on and off several times while watching the fuel pressure. How many cycles of the key does it take to get the fuel pressure up to spec? From what I can gather from others, these engines need at least 45-50 psi to start. Spec, as you know is about 60 psi.

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