93 Blazer Intermittant fuel pump

[Spectria, L1 MT]

I bought this car off Craigslist, said it had 3 fuel pumps in 6 months and couldn't afford anymore. 4.3 Vortec, Port injection.

Paid $450, and towed it home.

I test for fuel pump sound, nothing.

I tested for fuel flow out of filter on frame rail, had lots of fuel, Odd.

Got fuel pressure tester on fuel rail and had 22 PSI, must be the Pump.

Bought a new Delphi Pump and Sock at Napa, $94 bucks.

Again against all recommendations, cut hole above sender/pump mount and removed pump. It was new, with new sock, didn't look as quality as the Delphi unit.

Replaced with Delphi Unit, and got 64 PSI KOEO, engine started right away, Pressure oscillated at 55 PSI KOER.

Luckily I didn't give this car to my youngest daughter for her very first car, instead drove it the next day about 50 miles to a job, wouldn't restart after parking.

Since I still had all the tools in the vehicle from the fuel pump "repair",
I was able to check voltage to the pump at the connector by rear bumper.

Had 12 volts at crank, stayed on for 3 seconds, and went to zero volts. Retested multiple times, did this each time.

Reconnected to pump harness, no fuel pump sound. Used DVM to check the ground which I had sanded on reinstall yesterday, and had no resistance to ground.

Thank God I had cut the hole in the WRONG place ( ).

Pulled pump out of tank and reconnected under car, after draining of fuel.

With assistant, went to Key On Engine Crank, no pump operation.

Now using my Junk Yard mentality, and being stuck in the woods after a full day of work, I cut the wire to my License Plate Light and connected to the fuel pump lead after cutting to harness leading to computer.

Had assistant turn on headlights and Pump runs fine.

Reinstalled in tank, reloaded car of tools, and after turning on headlights and starting engine, drove home with no further problems.

The Question is, How do I see 12 volts at the lead to the Pump harness, and no voltage drop apparent to ground, and yet no pump operation.

I seem to have voltage but no amps.

Where does this voltage/power come from, a relay or directly from the computer?

PS, I replaced the computer with a known good one before attemping the original fuel pump tests, with no improvement.

Thanks for your help.

[brcidd]

You have voltage but NO amps-- so your test should have been- test voltage WITH fuel pump plugged in- and you would have had NO voltage--This is due to a bad connection or weak spot in the wiring somewhere- usually burnt contacts or corrosion- look for corrosion and melted, blackened contacts at all plugs- at the fuel pump connector and including the fuel pump relay internal contacts (swap or replace relay if unsure) -Have even seen it in the oil pressure sending unit (a parallel fuel pump feed circuit). At some point in time the fuel pump(s) were pulling a lot of amps and probably melted a terminal pin or receptacle connector- could also be a damaged lead wire (gray) that is "hanging on by a thread" that can't carry the amps- but shows voltage-- so look for damaged wire to the fuel pump... Good luck

[Spectria, L1 MT]

Originally Posted by brcidd

You have voltage but NO amps-- so your test should have been- test voltage WITH fuel pump plugged in- and you would have had NO voltage--This is due to a bad connection or weak spot in the wiring somewhere- usually burnt contacts or corrosion- look for corrosion and melted, blackened contacts at all plugs- at the fuel pump connector and including the fuel pump relay internal contacts (swap or replace relay if unsure) -Have even seen it in the oil pressure sending unit (a parallel fuel pump feed circuit). At some point in time the fuel pump(s) were pulling a lot of amps and probably melted a terminal pin or receptacle connector- could also be a damaged lead wire (gray) that is "hanging on by a thread" that can't carry the amps- but shows voltage-- so look for damaged wire to the fuel pump... Good luck

Thanks for the response. so just to be clear, there is a fuel pump relay on this 93 Blazer?

You're right about the test, of course, should have tested with load, would have seen voltage drop.

The harness at the pump is very clean, will post back after I check further.

[brcidd]

Yours is the old box style blazer I assume-- FP relay is usually on firewall- passenger side

[Spectria, L1 MT]

Originally Posted by brcidd

Yours is the old box style blazer I assume-- FP relay is usually on firewall- passenger side

Owe ( )

Yes it is the OLD style box (which I like, as well as the newer curvy ones.

Thanks for the hint, I did locate the relay, haven't had a spare minute to check the connections and the relay.

Thanks!!