Extended crank

[BruceK]

When my truck sets for longer than four hours it is very hard to start, acts like it has run out of fuel. It has been getting progressively worse.

 

Fuel pressure: 30-34 PSI, fluctuates at idle.

When shut down pressure goes to 35-37 PSI after about five minutes, suspect heat from engine is causing this rise in pressure.

Pressure keeps dropping until it gets to zero in about three hours.

 

According to the manual the pressure is low should be about 60 psi. Is the pump defective or is the pressure regulator the source of this issue? I pulled the vacuum line off of the regulator and there was no fuel in the line.

[Jsdirt]

Shocked it even runs at those pressures. Probably time for a fuel pump and a regulator.

 

Before throwing those parts at it, test the power and ground wires to the pump - make sure the pump is getting full power, and not half or less due to a bad connection somewhere.

[Jglew82]

If you can , block off the return line, then test your rail pressure. If it goes to 60, then you have a bad regulator. If it's still low, you either have a bad pump, pump wiring, restriction, etc. 

[Jsdirt]

Great test I neglected to mention. Thanks Greg.

[davester]

It'll run at low pressures, just poorly.  When I bought my truck, it's fuel pump could put out 50 psi at idle, but revving the engine up to 3K, pressure would drop to about 15 psi and stay there.  The ecm tries to work around it by leaving the injectors open longer, but the main problem is they don't spray right.

 

Anyway, time for a new fuel pump.  It's possible the FPR has failed (it can fail without fuel coming out the vacuum line), so you may want to replace it first (cheaper and easier to do), but it's more likely the pump is finally failing.

[Doug_Scott]

What about the filter?  Does it have an external fuel filter?  From your description, it really sounds like a plugged fuel filter.

[riverbanks]

The only way I found out to block return is,deadhead at the filter,any other ideas?

[Jsdirt]

I'm thinking your gauge may be skewed. If you could get another gauge and compare readings, that could confirm that. I've never seen one of these run on pressure that low.

 

We are talking about your '03 listed under your username and avatar, right?

[Jsdirt]

43 minutes ago, riverbanks said:

The only way I found out to block return is,deadhead at the filter,any other ideas?

I always wrap some inner tube around the return line right up in the engine compartment, and lock needle nosed vice grips on it.

[Doug_Scott]

11 hours ago, riverbanks said:

The only way I found out to block return is,deadhead at the filter,any other ideas?

"Deadhead at the filter"?  Do you mean the fuel filter?  If you have a fuel filter outside of the fuel tank, your truck will behave like you describe if it is plugged.  If you do not mean the fuel filter then you will need to provide more details in regards to what this vehicle is. 

[riverbanks]

Not my truck,I was just asking for a alternative method from the contributers on this thread,and I got one,thanks

[BruceK]

16 hours ago, Jsdirt said:

I'm thinking your gauge may be skewed. If you could get another gauge and compare readings, that could confirm that. I've never seen one of these run on pressure that low.

 

We are talking about your '03 listed under your username and avatar, right?

Yes, 2003 GMC 5.3L with an external filter (in the left frame rail).

[BruceK]

20 hours ago, Doug_Scott said:

What about the filter?  Does it have an external fuel filter?  From your description, it really sounds like a plugged fuel filter.

Yes it has an external filter (left frame rail)

[Doug_Scott]

1 hour ago, BruceK said:

Yes it has an external filter (left frame rail)

You will want to change it if you have not done it in the last 50,000 miles.  If that corrects it, your pump won't be far behind due to the restriction in the system.

[BruceK]

3 hours ago, Doug_Scott said:

You will want to change it if you have not done it in the last 50,000 miles.  If that corrects it, your pump won't be far behind due to the restriction in the system.

I changed the filter 18,000 miles ago. It should be okay I only purchase gas from one source and no problems with other vehicles. One of the suggestions was to replace the fuel pressure regulator as it was only a few dollars. According to my research this valve is almost eighty dollars. Do you think this is a wise move?