2000 Silverado 5.3L fuel pressure still low after new pump and more...

2kchevy · December 9, 2019

2000 Silverado 5.3L 2WD 1500 RCSB w/ ~165Kmi - all stock
Fuel pressure still just under spec after new pump and more...

I replaced the fuel pump (AC Delco OEM) and the new pump made only a slight difference and pressure is still out of spec. The new pump pushes about 2psi more pressure and draws 2amps less.

Spec per Haynes:
55-62psi key On / engine Off

Old pump:
52psi key On / engine Off
48psi at idle
56psi at idle when you pull the vacuum line from the regulator
Amp draw 8.5amps

New pump: 54psi key On / engine Off
Flutters between 48-50psi at idle
58psi at idle when you pull the vacuum line from the regulator
Amp draw 6.3amps

Fuel pressure regulator vacuum line is dry and no obvious signs of failure / fuel leakage and also see the readings above with the FPR vacuum line removed.

Measured the voltage drop for each the power and ground circuits and that checks out as well. Voltage drop is ~0.1v on the ground and ~0.5v on the power with the truck running. Battery only (i.e. not running) ~0.1v on the ground and ~0.4v on the power. Measurements taken from the battery post to the pump connector. Pump is also getting 14v while the engine is running (~14.6v at the battery).

Removed the fuel filter and blew out the supply line from the pump back to where the filter would be then switched sides and blew out from the supply line at the rail to where the filter would be and it did not make any difference. The fuel filter was changed about 2 months prior to the new pump in an effort to fix the low fuel pressure but did not make any difference.

So all that and the fuel pressure is still lower than the spec. of 55-62psi key On / engine Off.

What should I try next?
What does your fuel pressure normally read key On / engine Off or at idle for a 5.3L of this vintage with return systems?

Thanks.

Brian715 · December 9, 2019

What caused you to check the fuel pressure? Does it run poorly? Do you have misfires or fuel starvation issues?

2kchevy · December 10, 2019

Truck completely died twice a few months ago on two different trips. Once while accelerating to get on the freeway after I had already been driving ~30min without any issues and once while idling in park, again after I had already been driving ~30min. No misfires or trouble codes I am aware of. Other than those two times the truck has always run great and still does today. Test driving after the new pump I nailed it going ~30mph and after down shifting to 1st it spun the tires until shifting into 2nd, so seems healthy.

davester · December 10, 2019

You might consider replacing the FPR.

And you might consider testing fuel pressure when the engine is going faster (that was the problem with my truck, at idle the fuel pump could get it up to 55 psi, but once the engine was going faster, the pressure would drop way down). Note, the pressure may drop for a short time as the engine is speeding up, but should quickly return to full pressure once the rpm's become constant again.