Thanks George, I plan to jump the pump to the battery, and see what I get (assuming I have the correct connectors for the pump outlet and my pressure gauge). I managed to drop the tank, but unfortunately one of the plastic connectors on the pump broke during removal. When I was wiggling the filler hose to try to get it loose, it tugged on one of the lines that was still connected and snapped the it off (the one closest to the im driver side, I believe it's the return line). I Have ordered a new pump and it's arrived but of course it did not come with wiring instructions for the new harness. I see Captain Hook mentioned in this post https://blazerforum.com/forum/2nd-ge...sue-84309/that I need to wire two of the wires together to ground (black and orange), do the other two need to be wired to the remaining two on the original harness? - [ ] From the wiring diagram in the Haynes manual it looks like the two are grey and purple that need to be connected. A few questions from looking at that: according to the diagram, the fuel pump oil pressure switch is apparently wired in parallel with the fuel pump relay. There are some theories on the internet that this is a shutoff switch if the oil pressure drops, but they would need to be wired in series to function as a shutoff. Is it just an erroneous diagram? Also, what's the second wiring harness on the pump for?

 

There are four harness wires and four fuel pump assembly wires. The colors will not necessarily match up . On the harness:

1. Gray: pump 12v
2. Purple: fuel gauge positive
3. Black: pump motor ground which goes to the frame
4. Black/white: fuel gauge sender ground which goes to a junction block to be merged with the fuel tank pressure ground and then on to the engine computer. This is a conditioned ground not frame ground

The oil pressure switch is wired directly to the gauge cluster and is not involved in the fuel pump relay circuit.

George

 

Thanks. I've been out of town for a few weeks but have progress. I jumped the old pump (wired it straight to the battery), and it was showing the same low pressure as before. The tank looked spotless on the inside (just pale plastic, no grime, grit or debris) so I drained the tank, rinsed it out with clean fuel and added a few gallons. I installed the new pump, checked the pressure as above - over 80 PSI when I opened the circuit, and held steady down between 60 and 70 after about ten minutes. I didn't have time to fully reinstall the tank and rewire, but I propped it up, got the front band attached, reconnected all the hoses and closed the circuit with the old wires with alligator clips. Turned the key and it started right up and ran without any sputtering or issues for several minutes. I'm planning to get back over there in the next few days to finalize the wiring and secure the tank. There's a pretty loud squeal now coming from the engine compartment, but hoping that's just related to it been sitting for a while.

 

Here's some photos of my test setup for anyone else looking to do the same:

Test setup straight from the battery. 3/8-16 machine screws thread into the battery connection ports.

Clamped old harness to frame, used sewing pins for connection.

12w test lamp wired up to the harness with cheap voltmeter. Alligator clips go to harness as in other photo.