95 gmc sierra 5 speed. I have replaced every sensor, relay, fuel pump was replaced 4 years ago and just swapped computer today. I installed a MSD distributor and coil last weekend but the this problem is intermittent. I checked power on ignition switch before and after plug in to wire harness underneath dash. All fuses and relays except fuel pump relay has power but 2 grounds show good ground and power wire shows 2.4 volts. Now i jump wire from bypass wire at the fuse box in engine bay and pump turns on fine but turn of the ignition and no pump primes and no relay click. I think pcm is not communicating or maybe a bad fuse link with relay. I have more testing to do this weekend. Plus i do have a new pump and sending unit to install this weekend as well my fuel gauge stopped working.

 

fuel pump relay wont have power except when the key is first turned on to prime the lines and when the engine is running. do you have duel tanks?

 

thanks for the wiring diagram, the fuel pump works fine when i jump power to the test connector and pump turns on fine. With ignition on relay does not kick nor fuel pump primes. Since i have been going thru computer twice already im gonna check power and ground at the plugs for the computer and see if i have a ground issue at the computer. That will cause a burn out and eventually communication issues

 

is your ecm A & B fuse still good? mind you im more into the 87-91 tbi units in the squares but they should share the same electrical setups

 

does it stay running if you jump the fuel relay, then start it, then unhook the jumper wire

 

I realize you have checked power at the ignition to fuel pump with (I assume ) switch in run. Is this the original switch? Could be an issue with the switch in crank position. You post the pump does run with a jumper, just a thought.

 

interesting thought on that i did replace the ignition switch a month or 2 ago and yes the fuses are in good condition i changed all of them year ago. I checked system ground wires to ecu and got good readings the relay was even showing good ground at ecu plug in. So im gonna go thru my grounds and replace 2 ground straps since they are as old as the truck. But maybe a ignition switch issue cant remember if its a reman or new part got it from A1 Auto