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1998 Chevy 5.7 hard start.


brown1911
11-13-2008, 08:27 PM
Hello everyone thanks for taking the time to look at my post. I have a repair shop here in Tennessee, and I use the forum quite often to solve problems. This problem I have not been able to find anyone with the same. The truck sometimes would not start immediately, it would just spin over and over before it would finally crank. I put a pressure gauge on and it showed 60psi. I noticed after a while the reading would fall off to about 40-45, this is after shutting off engine. Doing some research I found that forum members have found pressure regulators to go bad. The truck has the infamous intake gasket leak, so I sold the customer on the idea that the regulator was bad, and that it needed a intake gasket replacement. Lets kill two bird with one stone. I completed the intake repair also replacing the regulator while intake was off the truck. Problems solved right? Well partly, stopped the coolant leak, but my cold start problem is worse. This morning truck started right off, drove to town, shut it off to go into store, came back out, and boom NO START. Engine just spins. Turned key off back on, engine spins over several times, and finally starts. Get truck back to shop, stick a guage on it have 60 psi truck starts right up. Now it gets tricky. After truck sits there for about 15-30 mins pressure had dropped off to about 45 psi. Turned key on for 2 sec prime. I hear the pump running, but pressure would not come back up. Turned the key back off and back on and it will not build up pressure. Tried to crank engine, and all it would do is spin. I relived the pressure off the gauge and turned the key back on, and boom 60 psi. Truck starts. It will continue to start as long as you dont let it set any length of time. I hope all this helps, and iff I have left something out please feel free to ask. Thanks for listening and look forward to your response.

discnik
11-14-2008, 12:32 AM
Had a 99 S-10 truck do the same thing. Turned out the fuel pump was on its way to BOOT HILL. Replaced pump no prob.

MT-2500
11-14-2008, 09:55 AM
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.

brown1911
11-15-2008, 07:52 PM
I will post back fuel pressure readings Monday.

brown1911
11-17-2008, 11:33 AM
Fuel pressure readings on Monday the 17th of Nov.

Initial 2 sec prime 60 psi

Engine cranks and pressure drops to about 54 psi

After engine warm-up take for a test drive crusing speed 50-54 psi

Under acceleration 60 psi this is about a 15 min drive.

After return from test drive shut engine off, and pressure was holding at 50 after a few seconds the gauge rose to 60 psi no key on.

After 15 min pressure held at 60 psi. Attempted to start engine it cranked and run for about 2-3 sec. died and pressure had dropped to 40 psi after this. Turned key back off the on pressure jumped back up and engine refired and maintain idle.

This series of events happens every time engine sits for more than 10 minutes or so. First thing in the morning engine cranks and runs fine.

MT-2500, What is your thoughts on this?

Thanks

MT-2500
11-18-2008, 10:11 AM
Fuel pump may be weak But first.
Check full fuel pump pressure.
Block off return line or check dirrect at fule filter in line.
Fuel pump needs full pressure 85 -95 lbs for pressure regulator to hold good fuel pressure.

j cAT
11-18-2008, 10:38 AM
this is most likely the fuel pump ...just to be sure measure the voltage at pump connector and check the ground at tank for security..

the pressures are low sometimes this could be caused by a poor feed/ground connection....to pump...as well as the relay../wires..

with the engine running check the voltages

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