Fuel Pump - Time to Replace or Not??

[blk95lumina]

Hello.

2000 Silverado 1500 w/ 5.3L
Truck has ~165K but pump was replaced around 55K so pump has ~110K.
Previous pump replacement was a dealership mistake (replaced under warranty) as the real problem ended up a bad / ruptured regulator.

I just replaced the fuel filter and vacuum line on the regulator as it was cracked and did not see fuel coming out of the regulator nor was it wet inside the vacuum line after running.

Fuel pressures at the rail are...

52psi key On / engine Off
48psi at idle
56psi at idle when you pull the vacuum line from the regulator

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

Should I replace the pump?

Thanks.

[j cAT]

I own a 2000 silverado 5.3L .. owning it for close to 20 yrs.. fuel pressure must be 52 psi and higher @idle............... normally my pressure is 56psi @ idle. any fuel pressure below 52 PSI will cause problems .removal of the vac line on reg should rise to 60PSI. my guess is the fuel pump ground and power connector on the pump at the fuel tank / frame ground .. frame ground could be rusted so clean it up.. see how the pump works. if you operate the truck fuel level below 1/4 tank of gas then the pump does die slowly . pump current should use 5-6 amps .... if its 4amps or less after the connector / ground checks ,, the pump has problems or the internal tank wiring connectors ..

[blk95lumina]

Thanks j cAT!

For the ground, are you referring to the frame ground located underneath the driver's side door? Or is there another frame ground near the tank? This is a reg cab 1500.

What is the easiest way to check the pump amperage draw?

Is there a way to check the power connector at the pump without dropping the tank or lifting the bed?...maybe somewhere I can back probe and check for resistance? And if so, what should the resistance be on a good power connector and pump combination?

Thanks.

[blk95lumina]

I checked the frame ground under the driver side door and it still looked good. Years ago I was getting an ABS trouble code so I removed the frame ground, wire brushed the frame area clean, reinstalled, and painted over it (ended up being a bad relay in the module so I had it rebuilt).

Tested the pump amp draw by removing the relay and using a DMM (had to use wires as the probes could not reach the contacts) and the pump is drawing high at 8.5amps.

I had replaced the fuel filter a few weeks ago as a first attempt to fix the low pressure. So maybe I have a restriction somewhere or a clogged pump.

I went ahead and ordered a new pump (AC Delco MU1613).

Will move forward with dropping the tank and replacing it unless there is somewhere else in the system I can check for a restriction.

[j cAT]

current is a little bit high on the pump.. should be 6 amps ..
lift the bed to do the work. reason is you do not have to suck the gas out and also do the testing of the pressure and how the engine runs ... then when its fixed drop the back back in place.. dropping the tank can cause problems/ break stuff..then you have to put it back up to do the testing .. more work .

many that had GM tahoes/suburbans it was a nasty job unless you have a lift .

some on those tahoes cut a hole in the floor ..
many manufactures have doors for access to the fuel pump...
some aftermarket fuel pumps use higher current 10 amps.. I never use those because GM does not have the wiring and relays to handle the high amps.

[brcidd]

Yes, I always lift the bed on a pick-up..much easier, and usually only 6 bolts. I have used my engine puller hoist, and even an overhead beam with a come-along works....

[blk95lumina]

Thanks for the tips. I was considering lifting the bed but it is just the wife and I and I do not have a lift or overhead beam.

Any suggestions on how to do this safely? Can I just prop up one side? Or maybe one person on each side can slide the bed towards the rear enough to clear the tank?

Thanks.

[Blue Bowtie]

If you are careful, and have a means to support the bed, this can work:



I stacked 4x4 sections under the bed after lifting a little at a time. 12" is plenty of room to access the tank top unit if you can manipulate the well/springs out of the hole.

[blk95lumina]

So just replaced the pump and ran some tests while I still have the bed up. New pump made only a slight difference and pressure is still out of spec. 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 at idle
Amp draw 8.5amps

New pump:
54psi key On / engine Off
Flutters between 48-50psi at idle
58psi with vacuum line removed from pressure regulator at idle
Amp draw 6.3amps

Double checked the lines at the pump while idling and no leaks.

Maybe there is blockage somewhere in between the pump and rail?
I replaced the filter just a couple months ago.

Any other ideas?

Thanks.

[blk95lumina]

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 2psi difference between the old and new pumps may just be the variance as it measures 52-54psi key on engine off and 48-50psi at idle. When watching the gauge as the key is first turned On the gauge shows 57psi for the couple seconds the pump is running and then drops to 52psi immediately once the pump stops. It then bleeds down to 50psi in 10-15sec.

[blk95lumina]

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).

The slight pressure bleed off mentioned earlier may have been the gauge as when I was done with this last round of tests the gauge held at 54psi even 10min after turning off the engine. Of course the heat then coming off the engine and into the rail and fuel gauge line can influence that.

Other than replacing the fuel pressure regulator just to try it I am out of ideas and plan to re-install the bed tomorrow and call it done.

Any other ideas?

Thanks.

[blk95lumina]

***WARNING LONG UPDATE***

Last week 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.

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.

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?

[Stealthee]

Had a similar occurrence with my brother's XJ Cherokee. It died and wouldn't restart. Pounded on the tank and it fired up. Replaced the pump and it didn't start. After doing more diagnosis we found it had ate another crank sensor.