TBI fuel pump low voltage

[TPI84GMC]

Hey all,
I’m working on a 1989 squarebody , I know not 73-87, Suburban v2500 with TBI. It’s been sitting for about 8 years and the fuel pump won’t run. I jumped the positive wire in the harness to 12V at the battery and the fuel pump works. Checking voltage at the connector near the tank at the back of the vehicle it only shows 8 volts. I changed the fuel pump relay. No change. Unhooked the oil pressure switch. No change. Replaced the oil pressure switch. No change. Still 8V at the pump. Any other ideas on what could be my issue?

It does have an aftermarket alarm installed and I’m wondering if that’s the culprit. Would that make sense that it could be interfering and causing only 8V to be available at the pump?

Thanks!


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[VileZambonie]

What's the battery voltage at the battery? How are you measuring the voltage? Make sure the wire is disconnected from the pump, and your meter lead connections are good. If you are applying 12 volts to the jumper wire and only receiving 8 volts at the end of the wire, then the wire needs to be replaced. However, I would double check your readings.

[TPI84GMC]

Thanks for the reply! I’m checking it with the plug disconnected with the negative lead on the meter grounded to the frame. Battery is brand new 12.7 volts snd everything else on board appears to be working correctly.

If I run a new + wire how far up should I run it? All the way to the relay? Does the + wire run through the ECM between the relay and pump?

I’m having a hard time finding a wiring diagram for some reason showing TBI wiring for 1989.

Thanks again!


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[VileZambonie]

If you have 12 volts at the end of the jumper and 8 volts at the pump there is a problem. Double check before going down a rabbit hole.

[TPI84GMC]

Update! I did some more chasing tonight and if I put 12V to the jumper wire the fuel pump shows 12V at the connector CD Ed drdtgt aaa as well... went back and checked to see if I was just crazy with the 8V reading and sure enough still 8V with the jumper wire unhooked and key in run position... open to ideas here...


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[VileZambonie]

What is "CD Ed drdtgt aaa" ? With the power off, Set your meter to ohms and measure the resistance through the pigtail to the end of the wire. Do the same on the ground side where you are connecting your meter. If you are dropping 4 volts through the wire, you have resistance and need to replace that wire. Is there butchery in the harness?

[TPI84GMC]

Didn’t get that far but when I looked up under the dash I realized the aftermarket alarm had some issues. Missing fuse and disconnected wires. Hooked everything back up and now the fuel pump at least operates now when the key is in run. Gotta get the lines all connected back and should be able to see if I can get it running this weekend. Thanks for continued support.


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