Hard starting cold and hot

[03'Silverado2500HD]

I have a 2003 silverado 2500hd with the 6.0 (LQ4). It's been having a hard time starting for a few months and I have been able to avoid the problem by cycling the fuel pump with the key a few times. What happens is the engine will crank for a while and either not start on first attempt or will sputter to life slowly. Sometimes a second cranking cycle is required.  Current list of mods and replacement parts include cold air intake intake/ flow master exhaust and Blackbear 91 tune. I have replaced the fuel filter with a high flow spin on filter and also replaced the fuel pressure regulator. I don't beleive it's a result of the tune because it had the issue every once and a while before the tune. (The tune is about 3 months old) My next step is either replace the fuel pump or injectors. Any help is greatly appreciated! 

[Swimmer8366]

Do leak down test first. If is leaking down. Pull rails and check injectors for leak down.

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[davester]

yeah, check fuel pressure at the rail.  If you have the 'return' style fuel system (not sure when GM switched from return to returnless, it was either '03 or '04 I believe), could also be the fuel pressure regulator on the fuel rail that's a problem.

[txab]

2004 returnless

[dewfpo]

It's not going to be your injectors. It sounds like a fuel pressure.pump issue.

DEWFPO

[03'Silverado2500HD]

On 10/20/2017 at 10:48 PM, davester said:

yeah, check fuel pressure at the rail.  If you have the 'return' style fuel system (not sure when GM switched from return to returnless, it was either '03 or '04 I believe), could also be the fuel pressure regulator on the fuel rail that's a problem.

I replaced the fuel pressure regulator already and didn't solve problem. And there is no pressure at the rail if I depress the Schrader valve nothing comes out. Yes my truck does have a fuel return system. 

Edited October 22, 2017 by 03'Silverado2500HD

[03'Silverado2500HD]

18 hours ago, dewfpo said:

It's not going to be your injectors. It sounds like a fuel pressure.pump issue.

DEWFPO

Is there a way to test the checkvalve in the pump? The pump is supplying enough fuel to support WOT. If I prime the pump with the key 2 times it will usually start right away. 

[Silverado4x4]

Fuel pump is gone, replace it.

[dewfpo]

Check the fuel pressure at the rail (it has a Schraeder valve on it so it's easy to test), with the engine running and with the engine off.  Check it 5 minutes after shutting off and 1 hr after shutting off.  It should maintain pressure.

 

DEWFPO

[03'Silverado2500HD]

21 hours ago, dewfpo said:

Check the fuel pressure at the rail (it has a Schraeder valve on it so it's easy to test), with the engine running and with the engine off.  Check it 5 minutes after shutting off and 1 hr after shutting off.  It should maintain pressure.

 

DEWFPO

I checked the pressure a few mouths ago when I first started to look into the problem and it was a little low. If I depress the Schrader valve core on the fuel rail an hour after running No pressure is released. But that tells me there is no pressure, so it either going back to the tank from the fuel pump or leaking from an injector. 

[dewfpo]

If fuel were leaking from an injector, the fuel pump would still be able to build and maintain pressure with the key on.  If you had a bad injector, you would see indications of it on the spark plug(s).  One would be black compared to the others.

 

If you turn your key on, the pump should come on, build pressure and then turn off unless the check valve is bad, there is a leak or the pump is failing.

 

Attach a fuel pressure gauge to the rail and turn your key on, see what pressure you have and see how quickly it bleeds down with the key on and the key off.

 

You could also pull your plugs and look for a fouled one.

 

Does your oil smell like gasoline?

 

DEWFPO

 

 

[Raptordude]

How many miles are on the truck?


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[03'Silverado2500HD]

16 hours ago, Raptordude said:

How many miles are on the truck?


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Just turned 96,000 

[Raptordude]

That's a little early for a fuel pump...it does sound like your issue though


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[03'Silverado2500HD]

The fuel pressure with the key on engine off is 60psi. As soon as the pump stops priming it immediately goes back down to 0 psi. With the engine running it's at like 48psi and when I throttle up it drops to 45 at best. I think the check valve and pump are going. I don't think a injector could loose the much fuel in a second and once primed it starts right away. The oil does not smell like fuel and I replaced the spark plugs about 3,000 miles ago and I was having the problem then too and all the plugs looked really good nice very llight brown. 

Edited October 28, 2017 by 03'Silverado2500HD