1994 Suburban 1500, 8 volts at fuel pump

[ryanguy426]

I'm back again with my never ending Suburban project

1994 Suburban 1500, 350 TBI. I put in a new Delphi fuel pump, and the truck ran great, started easily and consistently. The truck sat for 2 weeks, it's now a no start, and only 8-8.5 volts at the fuel pump connector. Code 54. Can't hear the pump running whatsoever even with an ear to the tank.

Any diagnostic tips? I already swapped the pump relay with the one on my Sierra, same result. Put 12v to the gray wire out of the relay, nothing. Jumped pin G on the ALDL connector with 12v, nothing. Cranking until the oil pressure hits 40, and nothing.

Runs fine if putting gas or starting fluid down the TBI.
My instinct is telling me to throw another pump at it, but the 8 volts at the connector tells me it's somewhere on the truck and not the pump. Curious if there might be something common I'm overlooking maybe? There's nothing obvious.

 

[88monteSS]

If you're only getting 8v at the connector I would suspect a wiring issue, probably corrosion somewhere between the relay & the tank.

Sent from my XT1254 using Tapatalk

 

[Gramps]

And don’t forget to check, and clean/tighten the fuel pump ground on the frame

 

[PlayingWithTBI]

And don’t forget to check, and clean/tighten the fuel pump ground on the frame

^^^X2 - I was just typing the same thing - Also check your grounds, did you clean them when you changed the pump?

 

[ryanguy426]

And don’t forget to check, and clean/tighten the fuel pump ground on the frame

Valid point, didn't see one by the tank/pump though, unless the ground is the bolt that attaches the connector to the frame? I took a wire brush to that bolt and part of the frame when I originally put the pump in. Or is there a ground somewhere in the engine bay for it?

 

[Supercharged111]

Valid point, didn't see one by the tank/pump though, unless the ground is the bolt that attaches the connector to the frame? I took a wire brush to that bolt and part of the frame when I originally put the pump in. Or is there a ground somewhere in the engine bay for it?

The bolt that holds the connector to the frame should also hold down the ground there with an eyelet terminal.

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You can see the bolt in this picture. It's not securing the connector here because at the time the truck had a boost a pump plugged inline.

 

[ryanguy426]

The bolt that holds the connector to the frame should also hold down the ground there with an eyelet terminal.

Uh-oh. I don't recall seeing anything like that originally... maybe someone else was in there before I bought the truck and they didn't attach it? I'll dig around and see if maybe it's tucked in somewhere.

 

[Supercharged111]

I snuck a pic in above for you.

 

[Schurkey]

There's multiple possibilities.

A seized fuel pump wouldn't make much if any noise, and amperage draw would be very high (at least until the brushes/armature burned) High amperage draw would reduce voltage.

Corroded wires or corroded connectors would reduce voltage.

Burnt relay or oil pressure switch contacts would reduce voltage.

GM is kinda infamous for using undersized wire on the fuel pump wire harness. Not unusual for system voltage to be 14, voltage at the pump to be only 12.5, and another 1 volt lost on the ground side. But if you've only got 8 volts on the supply, you've got problems. IS THE BATTERY CHARGED?

Do you have a low-amperage current probe? Many multimeters can test up to 10 amperes, but they may pop fuses or have other problems above 10 amps. Normal amperage should be about 5--6--7, but if the pump has problems it could be more than that.

 

[ryanguy426]

Cleaned up the ground, getting 12v at the truck side of the plug now, looks like that was the issue! ....initially.

Still no fuel pump. Ran a jumper wire from the positive battery terminal to the gray wire on the fuel pump side of the plug, grounded to the frame by the tank, no fuel pump. Checked with a multi meter, 13.5 volts (truck is hooked up to a battery charger) through the plug. So the pump went out while the truck sat I guess? Is that common or am I just unlucky? This was the first pump replacement I've ever done.

When I put the pump in originally, I cleaned the tank with a cleaning kit that came with the Delphi pump (this kit specifically). I was able to get the tank about 99% clean using it. Made sure the pump was seated in the tank properly, hoses tight, once it was back together I filled up halfway, and never let it go anywhere near empty or even 1/4 tank level for the 1 week I drove it for. Really sucks my almost $200 Delphi pump just up and failed like that :/