2000 Silverado 5.3L fuel pressure still low after new pump I replaced the fuel pump (AC Delco OEM)…

blk95lumina

2000 Silverado 5.3L fuel pressure still low after new pump

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.

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?

Thanks.

Comments (9)
No. 1-4
blk95lumina
blk95lumina

And seems pounding on the bottom of the tank when I was stranded may just have been a coincidence it started again. Maybe the sensor just needed time to cool off to get right again or whatever is going on with it. Makes me think that if the crankshaft sensor is bad, then maybe the PCM keeps the fuel pump relay from switching On. Is that possible?

blk95lumina
blk95lumina

Update again...
So this time around when the truck had me temporarily stranded it had also thrown a code. P0336 - crankshaft sensor circuit range / performance. Anytime the truck had stalled prior there were never any DTCs that I could see. I replaced the crankshaft position sensor today (after doing all the obvious wire checks, etc.) so we will see how it goes. In thinking back through when this all started late last year, I could have always had an intermittent crankshaft sensor and mistakenly replaced the fuel pump. In any case the pump had over 100K so was due anyway. I was surprised to see the new sensor did not throw the P1336 CASE but maybe these older 5.3s are not as sensitive. The first attempt to start the truck it immediately died. The 2nd time it fired up and stayed running since. I still plan to perform a crankshaft sensor learning procedure before going back to daily driving...which does not happen these days much anyway with all the shutdowns.

blk95lumina
blk95lumina

Update: New AC Delco pump left me stranded yesterday after only 6 months
So looks like I got a lemon. I was driving down the highway and the truck started sputtering and just barely limping along. Once stopped on the access road, I turned the key but did not hear the pump pressurize. I swapped the pump relay and headlight relay (same relays) but still no go. Only after I pounded on the bottom of the fuel tank with my fist did the pump start working. It died one more time but once again started working after I pounded on the bottom of the fuel tank. This new AC Delco OEM pump is only 6 months old and as posted before the pressure at the rail never met spec right out of the box, even with replacing the filter and pressure regulator. Voltage drops are good (0.5v or less) and current draw is ~6A.

Any recommendations on a good quality replacement pump?
AC Delco part# MU1613

Scotty, PM me what you would charge for a pump swap. It is getting hot here in Houston and I may not be up for it again.

Thanks.

Scotty Kilmer
Scotty Kilmer

Editor

generally I would assume either regulator is weak, or you got a crappy pump. GM makes crap these days