I'm trying to diagnose my fuel pump problem by eliminating everything else first (sure beats changing out that pump). But I have a couple of questions:
1. Which relay is the fuel pump relay? There are 3 relays in the area next to the brake booster, two identical ones and one larger one right next to the booster.
2. I unplugged the connector attached above the rear differential. There are three wires on it. The center lead has 8.5 volts with the ignition on. The other two have no voltage. Is this typical? (The battery shows 12.6 volts at the teminals).

 

Does the fact that I'm only getting 8.5 volts at the rear of the car an indication of a problem up front? Does a bad fuel pump relay still send out a partial voltage flow?

 

You should only have power to the pump for a short period when you turn the key to "on." Then the pump comes back on when the engine is running (oil pressure switch?). Run some long jumpers or get someone to sit inside so you can check the leads for power right when the switch is turned on. If the contacts in the relay are burnt/corroded, you can definitely have low voltage coming out of it. I believe the center relay is for the fuel pump.
On my car, all three relays (MAF, MAF burn-off, fuel pump) are the same. I replaced them all with the same part number.
You want to be absolutely certain before you tackle that fuel pump. That is one job I do not want to do again!

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88 IROC with cobbled together (not by me)drivetrain, 86 (?) TPI unit on an '83 305,CE subframe connectors, Edelbrock strut tower brace, polygraphite bushings all around...it handles like a dream, but man is it hard to push!!

 

Make sure you check the fuel pump fuse above your battery.

 

Well I replaced the relay just to be sure. No Luck. I have voltage on the tan/white wire coming out of the relay (for a couple of seconds after turning the ignition on and while cranking the starter. So I guess that only leaves the fuel pump....

 

Do you hear the pump whine when you turn the key on?

I'd wonder about the 8.5volts...if you're getting that voltage with the pump disconnected, then the pump isn't the problem.

Low voltage can usually be traced to a bad ground or frayed wiring.