Fuel pressure drops

[suburban97]

I have a 1997 suburban K2500 5.7L, have starting problems and found fuel pressure drops from 60psi to 40psi after the 2-3sec priming. I pinched the return line and pressure holds. I just replaced the pressure regulator and no change. Does the return line go back into tank and just dump into tank?

[j cAT]

Originally Posted by suburban97

I have a 1997 suburban K2500 5.7L, have starting problems and found fuel pressure drops from 60psi to 40psi after the 2-3sec priming. I pinched the return line and pressure holds. I just replaced the pressure regulator and no change. Does the return line go back into tank and just dump into tank?

the return line is unused excess fuel .this goes back to tank..since you blocked the return line and the fuel pressure did not drop this is most always the fuel pump...some here have installed a check valve at the fuel filter to eliminate the need to replace the fuel pump..they appear to be successful..this will prevent pressure drop...

[MT-2500]

Originally Posted by suburban97

I have a 1997 suburban K2500 5.7L, have starting problems and found fuel pressure drops from 60psi to 40psi after the 2-3sec priming. I pinched the return line and pressure holds. I just replaced the pressure regulator and no change. Does the return line go back into tank and just dump into tank?

You should see 65 on prime up or engine cranking.

Fuel pressure drop back threw pump check valve will no hurt much if engine cranking or running pressure is good like up to par specs.
If pinching return line and pressure holds good the pressure drop is in fuel pressure regulator area.

Run the complete fuel pressure test.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
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.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding 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 in system.
Post back fuel pressure readings.