98 Suburban Hesitation

[moombaman]

I have a 5.7L K2500 that starts normally. It hesitates and pops thru the intake for the first 30-45 seconds of driving. I thought it had something to do with cold starts but even after its warm if I shut it off for 3-5 minutes it repeats the hesitation and pop. Could the fuel pressure regulator be leaking and causing the issue? I assume that until I burn off the excess fuel it runs weak. The fuel pump is 6 months old and the filter is new. Any help would be appreciated.

[j cAT]

Originally Posted by moombaman

I have a 5.7L K2500 that starts normally. It hesitates and pops thru the intake for the first 30-45 seconds of driving. I thought it had something to do with cold starts but even after its warm if I shut it off for 3-5 minutes it repeats the hesitation and pop. Could the fuel pressure regulator be leaking and causing the issue? I assume that until I burn off the excess fuel it runs weak. The fuel pump is 6 months old and the filter is new. Any help would be appreciated.

the ECT sensor should be checked for temperature/resistance ratio ...this is very probable the cause as the computer does not have the correct operating temp to adjust the fuel mixture.....but it is possible the air intake sensor or MAF is bad.....don't know for sure 98 set up on that...

[moombaman]

I am willing to try the ECT but I get repeated hesitation after shutdown and restart after only 3-5 minutes. I will look into the MAF sensor and the air intake sensor but it sure seems related to fuel. I probably need to check my fuel pressure before I get too excited. I think it normally should be 53-62psi but I am not sure what the shutdown pressure normally is. Does anyone have that info? Thanks for your info!

[j cAT]

Originally Posted by moombaman

I am willing to try the ECT but I get repeated hesitation after shutdown and restart after only 3-5 minutes. I will look into the MAF sensor and the air intake sensor but it sure seems related to fuel. I probably need to check my fuel pressure before I get too excited. I think it normally should be 53-62psi but I am not sure what the shutdown pressure normally is. Does anyone have that info? Thanks for your info!

if the fuel pressure is in this range with engine running and on shut down holds to within 5psi of the reading when engine running the fuel pump and regulator should be ok.... usually the pump check valve fails and on shut down pressure falls rapidly...then you will need new pump......

[moombaman]

I have concluded that I am experiencing lean popping at startup. If the vehicle runs 3-5 minutes it is fine. I need to check fuel pressure but dont have the tools. Any ideas?

[Q-Bert]

MT-2500's Fuel Pressure Test Cut-N-Paste:

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 and fuel pressure testing guide line.
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.