Quote:
Originally Posted by timberwolf1961
 1989 k 1500 350ci stalled, it fires on ether but I have no voltage reading at the 20 amp fuel pump fuse on the firewall.. The fuel pump relay clicks when key is turned on. I had no symptoms of a failing fuel pump which is only a couple years old. I then unplugged the oil pressure switch under the distributor and jumpered it and now I have 12.2 volts through the 20 amp fuse, but I did not hear the pump power up and it wont start. Help. |
If it's like my '88, the fuel pump fuse is fed by the fuel pump relay OR the oil pressure switch; and both of those source their power from the junction block on the firewall right beside the fuel pump fuse.
The fuel pump relay is triggered by the ECM at key-on for two seconds, then shut off until the ECM senses that the engine is cranking or running.
The fuel pump fuse is powered by either the FP relay or the oil pressure switch, or both.
If the fuse has power, the pump should be getting power via the tan/white wire, and therefore running.
If the fuse has power but the pump doesn't run, you've got defective wiring between fuse and pump; or between pump and ground (the pump grounds to the frame rail using a foot-long, single wire under the box) or a defective pump. The fuel pump ground is NOT one of the three wires in the fuel pump wiring harness--it's the separate wire.
There is a known, common problem with the wire harness INSIDE the tank. Most replacement fuel pumps come with a harness upgrade kit that supposedly fixes this problem. I just put a pump into my 300,000 mile '88; and there was just the faintest sign of overheating/melting at that trouble spot--but lots of folks have had problems with this. If you've installed a new pump, I'd have expected that this would already be updated...but you won't know if that's the problem without some additional diagnosis.
I can't tell from your description if the fuel pump fuse has power when the fuel pump relay is triggered by the ECM.