rumbler46

Help!!!!!!!!!!! I have done so much to my truck and it still does not start

I tested the fuel pressure and it is at 50psi and goes down to 40psi when cranking. Where is the Fuel pressure reg on a 5.7 throttle body engine?

Jeremy-WI

Its under the upper intake manifold, about a 2 hr job to replace

Blue Bowtie

He's right, you know.



It's the item with my Torx driver stuck in it (to adjust standing pressure before closing it up).

Don't immediately assume the regulator is the problem without diagnosing the low fuel pressure first.

rumbler46

Blue Bowtie,
What else can I do to diag that? I put a pressure gauge on the fuel line and as I stated before it is at 50 psi with fuel pump on and 40 psi during engine crank.

usamarshal

If the fuel pressure is only 50 when its not being turned over then you may need a new fuel pump....first thing I'd do is replace the fuel filter...check to see what the fuel pressure is then...should be 60-66 psi I believe...if its still around 50 psi then get a fuel pump....If your losing psi when you turn the ignition of then you may need a new FPR and fuel pump...sounds like a fuel pump problem though...I've replaced mine four times...the key is keeping fuel in the tank and replacing the fuel filter every 15,000 miles or so...hope this helps, Skip

MT-2500

Here is some guide lines on fuel pressure testing.
If pressure is low you need to test for full pressure from fuel pump.
A good strong fuel pump should put out 75 or more lbs direct pressure.
Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

__________________
Remember proper testing gives us the answer to many problems.
MT

usamarshal

Yes, exactly what he said...

rumbler46

We pinched off the return line and checked the fuel pressure. turned the key fuel pump went on and the pressure stayed at 45psi. My guess is the fuel pump is dying. I have never seen a fuel pump die a slow death. They either work, or dont. What do you guys think?

Blue Bowtie

I think you need to verify that the pump has a full 12-14V right at the tank before getting excited about changing the pump. There are several connections in the circuit, including the relay and socket, fuse in the UEC, wiring back from the relay socket in the UEC, and the most suspect is the one just inside the frame rail at the R wheel opening. There is also a ground connection adjacent to that connector which is subject to corrosion. That is the main ground for the pump, and must be clean and intact.

rumbler46

Well, this has to be a really strange thing. I went out to start my truck and decided to just give it a try like I do from time to time. It FREAKIN started!!!!! I just dont get it, dont care, as long as it starts and runs I am happy.