Well, the FP/ECU fuse in my '88 is blowing out. I'm figuring the pump is fried, but before I go dropping the axle and the tank to get to it I'm passing all my diagnostics info past you guys first.. I'm sure ya'll know how much I'm looking forward to dropping the tank...

FP Relay connected: Turn key on, fuse blows as soon as FP relay trips for prime.
FP Relay disconnected: Turn key on, fuse holds.
FP Relay disconnected: Attempt to start, fuse blows as soon as oil pressure builds enough to trip backup FP relay.
FP Relay connected: 0.0 ohms between ALDL terminal G and ground
FP Relay disconnected: ALDL terminal G open circuit

Anyone else smell the possibility of a simple short (heh.. simple.. yeh..), or are the electric in-tank pumps known show a short condition when blown? Death of the fuse was sudden and unexpected, no probs with the car in quite some time... I've gone through a half dozen fuses trying stuff... ugh.

If anyone has a helms diagnostic sheet for this, it would be most useful..

 

Tech,

The FP/ECM fuse is only blowing when the relay closes? The ECM is out of the picture, and the fuel pump wiring is very suspect. Before dropping the tank, check the wiring to the pump. Isolate it as close to the pump as you can, even if it means cutting and splicing a wire (just solder and seal the splice well). The dead short you are metering at the 'G' terminal is a good indication of the shorted wire as opposed to a dead pump. Make sure you are using the lowest resistance scale on your meter to test the pump and wiring.

 

Okay.. it seems the G terminal only trips the relay.. doesn't actually power the pump. SO.. I was sitting there with the DMM set to 20 Megaohm scale.. and prodding at the FP Prime wire (red).. it's not a short =\ However the pump's resistance increases as the slight current from the DMM is applied, and doesn't go back down.. for a brief second it would have read near zero, but at 20mohm scale it started increasing in leaps of Kohms... I'm pretty sure the pump itself is toast now.. Thanks anyway tho =)

Btw, the resistance at the pump does return to near zero after trying to power it up and it blowing the fuse...