Strange Starting Issue

dnwhoop02 · November 13, 2009

2002 GMC Sierra 1500 4.8L V8 150,000mi

The first time I try to start it, the engine just turns over and over and over but won't start. However, if I let go (key goes back to "on" position) and try starting again it fires right up. It doesn't matter how long I try to start it the first time (e.g. 0.5 sec or 5 sec), or how long I wait before attempt #2 (as in, I don't have to let it sit there for a while then try again. I can try again immediately and it starts). After starting, the truck runs fine.

I tested the fuel pressure using the test port on the crossover tube between the right and left fuel rail and observed the following:

At rest with the key off: low pressure, not even enough to make the gauge move
Turn the key to "on" position: Pressure jumps up to ~50psi for about 0.5 second, then drops back down to ~5-10psi.
If I try to start the vehicle during the split second while the pressure is at 50psi, it starts immediately.
If I try to start the vehicle after it has dropped back down, it turns over and over and over then anemically starts (but within a second or so it is running smoothly).

Any ideas?

jrod332 · November 13, 2009

maybe a fuel pump.

Nytemare · November 13, 2009

+1 on fuel pump

Could also be leaky injector. Is there fuel around the rails on the top of the engine.

As well...could be a leak in your line..do you get a smell of fuel at anytime when your outside your vehicle?

minibike132 · November 13, 2009

It's one of 3 things fuel pump, fuel pressure regulator or leaking injector. Correction one of 4 things, a leak anywhere. Alot of people are going to read regulator and tell you to pull off the vacuum line and see if there is fuel in it. Ignore that advice for this problem, the regulator can leak 2 ways, through a ruptured diaphram that will put it in the vacuum line or from broken or weak spring which will dump the fuel right back into the tank.

The only reliable way to narrow it down is to use fuel line shut off's to isolate the different parts of the fuel system. You could pull the injectors with them still hooked up to the rail and see if they leak with the key on but that is pretty labor intensive for a 1 in 4 shot at actually finding the issue.

dnwhoop02 · November 16, 2009

I haven't noticed any fuel around the injectors or fuel rails, or noticed a gasoline smell anywhere. The only other thing I know is that one of the little mesh panels in the little circular thingy inside the fuel pressure regulator is torn, but I figured that piece was only used as a filter and wouldn't cause any major issues if I didn't replace it right away.

For those mentioning the fuel pump... would the truck run fine if there was something wrong with the pump?

Nytemare · November 16, 2009

It could be the pump starting to fail, and the truck could still run fine yes.

I would replace the regulator if it looks like something is broken in there...its somewhere cheap to start.

minibike132 · November 17, 2009

I haven't noticed any fuel around the injectors or fuel rails, or noticed a gasoline smell anywhere. I didn't mean externally leaking I ment fuel gettin past the pintle when the injector should be closed. The only other thing I know is that one of the little mesh panels in the little circular thingy inside the fuel pressure regulator is torn, but I figured that piece was only used as a filter and wouldn't cause any major issues if I didn't replace it right away. I can't really comment on this without seeing it.

For those mentioning the fuel pump... would the truck run fine if there was something wrong with the pump? It could run fine but allow fuel to drain back when off.

dnwhoop02 · November 17, 2009

thanks for the suggestions... I guess I'll start with replacing the pressure regulator

mamatried01 · July 23, 2010

thanks for the suggestions... I guess I'll start with replacing the pressure regulator

I am having the same problem with my 2001 Z71, 4.8.

Replaced, plugs, plug wires, fuel filter, fuel regulator, and air filter with no change.

My original fuel pump did die about 16 months ago and I replaced it with one bought from Autozone. It is now passed it's 1 year warranty by 4 months of course.

A new one is another $270. I can't really afford, being out of work, to buy a new one if it's not going to fix the problem.

mamatried01 · August 22, 2010

thanks for the suggestions... I guess I'll start with replacing the pressure regulator

I am having the same problem with my 2001 Z71, 4.8.

Replaced, plugs, plug wires, fuel filter, fuel regulator, and air filter with no change.

My original fuel pump did die about 16 months ago and I replaced it with one bought from Autozone. It is now passed it's 1 year warranty by 4 months of course.

A new one is another $270. I can't really afford, being out of work, to buy a new one if it's not going to fix the problem.

Well bit the bullet and bought a new fuel pump. Found one around $100 cheaper than Autozone at ABC Auto. Put about 800 miles on it and the problem has disappeared.