1998 Tahoe 5.7 crank no start

[dexmann1]

Greetings, thanks in advance for any advice...

1998 Tahoe 4x4, 240K miles with a crank no-start condition. New aftermarket fuel pump, new AC-Delco Gold fuel pressure regulator.

Will start with starting fluid and run great with the exception of a slight stumble off-idle. Followed service manual trouble-shooting charts. With fuel return plugged, fuel pressure only hits 55psi consistently, even with constant power applied to the pump by jumping the fuel pump relay. Fuel pressure slowly drops slowly, but didn't actually record times/pressures.

Sometimes it will start when the ambient temperature is above 60ish degrees, although it struggles to fire the first time When running the fuel pressure goes up to 60 PSI when the throttle is blipped but stays 55psi when idling. The only explanation I can come up with is that the pump is getting 14.5v with the engine running, resulting in higher pressures than key on, engine off.

voltage is good at the fuel pump connector. Am I looking at a weak fuel pump out of the box? I didn't install the pump, but it apparently came with multiple connectors for different applications. I have access to a '99 suburban that supposedly has new injectors, not sure if they were upgraded to MP or if they are still the older CSFI.

Thanks again for any help.

 

[OR VietVet]

Welcome to the forum from Oregon.

You did not say why the pump was replaced. Was it to fix a crank and no start condition and now you have the additional problem? Was everything ok till you replaced the pump? Did you replace a fuel filter? Is this problem the same problem you had with the old fuel pump?

An aftermarket pump with multiple connectors for different applications doesn't sound good to me.

 

[dexmann1]

thanks for the welcome and reply.

Was running fine until driving about 30 miles then wouldn't restart after being parked for 30 minutes or so. on day Eventually started after multiple attempts with no changes. Same problem occurred a couple more times then someone else diagnosed it with "low fuel pressure" (not sure on actual PSI) so the fuel pump was replaced.

last fuel filter change is unknown, but as well as it runs after it starts, the ASSumption is the fuel filter isn't an issue (maybe a bad ASSumption)?

 

[OR VietVet]

thanks for the welcome and reply.

Was running fine until driving about 30 miles then wouldn't restart after being parked for 30 minutes or so. on day Eventually started after multiple attempts with no changes. Same problem occurred a couple more times then someone else diagnosed it with "low fuel pressure" (not sure on actual PSI) so the fuel pump was replaced.

last fuel filter change is unknown, but as well as it runs after it starts, the ASSumption is the fuel filter isn't an issue (maybe a bad ASSumption)?

Badly clogged fuel filters can overwork a pump and burn it up over time. It will also restrict fuel flow and can create pressure problems. The pressures can fluctuate with a clogged filter. Rule of thumb, "Replace fuel filters about every 20k to 25k miles, IMO, and EVERY TIME you replace a fuel pump. This may not help but need to eliminate the obvious.

How old are the ignition components?

 

[dexmann1]

the ignition components are unknown age as well (not my Tahoe). The 99 parts suburban with a 5.7 I have access to supposedly has fresh ignition components and injectors, I may pull the cap/wires/etc. This isn't a daily driver and no real desire to put much money into it.

I'll replace the fuel filter to eliminate it. Thanks again.

 

[east302]

Followed service manual trouble-shooting charts. With fuel return plugged, fuel pressure only hits 55psi consistently, even with constant power applied to the pump by jumping the fuel pump relay. Fuel pressure slowly drops slowly, but didn't actually record times/pressures.

That should deadhead the pump so that it didn’t increase does point to either a weak pump, excessive pressure drop (clogged filter) or a leak that the pump cannot overcome. Did you block the supply as well?

If it leaks down with the return open, it’s either going through an injector, the regulator or back through the pump.

With just the return blocked, a pressure loss is going to be through an injector or the pump check valve. If it had held, you’d know it was the regulator leaking.

If you pressurize and then close both the return and supply, any drop has to be through an injector or an external leak.

If you have a scanner, see what the coolant temperature sensor is reporting. An odd-ball reading can cause the computer to call for too much fuel. Holding the gas to the floor when cranking temporarily stops injector pulses (clear flood mode) so see if that changes anything.

Or, swap the sensor from your parts truck and see what it does. It’s the one by the thermostat.

 

[dexmann1]

no change with new fuel filter. I'll be back next month and will most likely just order an OEM pump. I'll also bring my scanner to check coolant temp readings. Thanks for everyone's responses.

 

[dexmann1]

Just to follow-up with resolution. Replaced the aftermarket pump with OEM and problem resolved. Thanks for the assistance.