2003 Silverado 1500hd 6.0 hard start.

duhzombie · July 23, 2019

First post here guys so I’m not 100% sure how this works but I’m desperate at this point. My 1500hd has had a hard start for over 4 months now. When I turn the key on almost every time it takes 2 try’s cranking before it starts. It all started when I had to replace my knock sensors. Pulled the intake and rails put in the new knock sensors along with new seals and harness and were all good. Then the hard start begins. Naturally I thought maybe an intake leak or something but checked all around with starter fluid and nothing. So next was to check the fuel lines and make sure they’re good. Checked the pressure and it seemed off from what I’ve read it should be. I was sitting at 45psi and it would slowly drop. My truck has 260k and the fuel pump has never been changed so I figured I’d change the pump. Same issue. So I check the pressure again and it seems to prime fine. Hits 60 psi and then back to 50 but then slowly over time it drops. I’m at a loss now. I have no idea where this drop off could be coming from or if it’s even fuel related at this point. I have no idea really at all. If there is anything that maybe I’m missing please let me know. Thanks!

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CamGTP · July 23, 2019

60 psi at key on is great and only bumping down to 50 is fine. The regulator can't hold pressure forever so the slow leak time over several minutes can be expected.

Maybe you've done these things but is the throttle body clean and when you flip the key on does it crack the blade and stay there?

Is the MAF clean?

Do you have access to a decent scan tool that could do a crank relearn to make sure everything is in sync with each other?

duhzombie · July 23, 2019

How long should it stay at 50psi? It seems like it may very slowly leaking down from 50 over time. Yeah the maf is clean. Hell I replaced that too thinking that was possibly it. I may be able to get a scanner to check it from a coworker.

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duhzombie · July 23, 2019

I have not checked the throttle body yet. It has been cleaned but I’ll check and see if it stays.

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davester · July 23, 2019

Does your have the return-style or returnless fuel system (ie, one line from the fuel tank, or two). If two, then you've also got a fuel filter inside the frame rail below the driver's seat you might consider changing if you haven't done it recently.

As well, if you have two fuel lines, then maybe the fuel pressure regulator at the rail is allowing the fuel to drain into the tank, so there's just air in the fuel rails, until you crank enough that the air bleeds out and you start getting fuel into the injectors.

duhzombie · July 23, 2019

Does your have the return-style or returnless fuel system (ie, one line from the fuel tank, or two). If two, then you've also got a fuel filter inside the frame rail below the driver's seat you might consider changing if you haven't done it recently.

As well, if you have two fuel lines, then maybe the fuel pressure regulator at the rail is allowing the fuel to drain into the tank, so there's just air in the fuel rails, until you crank enough that the air bleeds out and you start getting fuel into the injectors.

Mine is a return style. I have tried replacing the fuel filter on the frame. Idk about the pressure regulator but I have replaced it with a new one from O’Reilly’s. That sounds like what it could be though. Once it starts it seems to run just fine. Doesn’t run rough or anything at all. What should my pressure be at idle? Mines running at about 48psi at 500rpm.

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davester · July 23, 2019

2 minutes ago, duhzombie said:

Mine is a return style. I have tried replacing the fuel filter on the frame. Idk about the pressure regulator but I have replaced it with a new one from O’Reilly’s. That sounds like what it could be though. Once it starts it seems to run just fine. Doesn’t run rough or anything at all. What should my pressure be at idle? Mines running at about 48psi at 500rpm.

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I don't know the factory specs for your year, but for my truck ('04 with an LQ4 engine, returnless system), I believe fp was spec'ed to be in the 58-62 psi range, regardless of rpm. It should only drop briefly while the engine is revving up, and fairly quickly return to full pressure once the engine has stopped speeding up.

I would expect your fp should be the same.

duhzombie · July 23, 2019

I don't know the factory specs for your year, but for my truck ('04 with an LQ4 engine, returnless system), I believe fp was spec'ed to be in the 58-62 psi range, regardless of rpm. It should only drop briefly while the engine is revving up, and fairly quickly return to full pressure once the engine has stopped speeding up.

I would expect your fp should be the same.

Well damn. So maybe the new pump? I did try 2 pumps but they both idled at about 48 psi. Doesn’t seem to run rough or anything. Unfortunately I never checked the pressure before it had any issues so I really don’t know what it was before these issues.

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davester · July 23, 2019

I would probably first look at the FPR, maybe you can disable it to see if the fuel pump can get pressure up to 60 psi (or higher), then it's the FPR's job to reduce the pressure to the right range. Diagnose before throwing parts at it...

riverbanks · July 23, 2019

Have you tried cycling the key a few times? before cranking,that gets a good prime,and I think f.p.r also,and how does the starter sound,still cranking quickly?

duhzombie · July 23, 2019

I would probably first look at the FPR, maybe you can disable it to see if the fuel pump can get pressure up to 60 psi (or higher), then it's the FPR's job to reduce the pressure to the right range. Diagnose before throwing parts at it...

With the old FPR on I got the same issue. With the old one when I’d remove vacuum it would jump up to 60psi at idle new one does the same but the seal and the strained on the old one were pretty corroded so I decided to give that a shot since it was wore out anyway.

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duhzombie · July 23, 2019

Have you tried cycling the key a few times? before cranking,that gets a good prime,and I think f.p.r also,and how does the starter sound,still cranking quickly?

yes after cycling the key a few times it acts like it’s flooded or is just not getting any fuel at all and doesn’t really want to start. I thought this initially and thought maybe it was a defective pump. The starter sounds great still no hesitation and no grinding or pinging.

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riverbanks · July 23, 2019

Interesting,does your oil smell of fuel?and if it did flood,you would get a black cloud out exhaust,is that happening?

duhzombie · July 23, 2019

Interesting,does your oil smell of fuel?and if it did flood,you would get a black cloud out exhaust,is that happening?

No black cloud or anything like that. Oil just smells normal and when I did the oil change last nothing seemed out of the ordinary.

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duhzombie · July 23, 2019

It also seems pretty consistent on starting up fine at the beginning of the day with no real issues. After that first start damn near every time I go to start it whether it’s 30 min later or an hour it seems to have the hard start.

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