My fuel pump wont work with relay but will with jumpers ran to toggle switch in dash. i check all the wires between relay and pump and nothing is burnt or broken. I also tried putting new relay in, didn't help. any suggestions?

 

Can you hear the relays clicking when you first turn on the key?

Did you try replacing the ECM relay next to it? That is what activates the pump relay.

Also did you do a voltage test at the relays to see if you had voltage to and out of the relays?

 

its hard to hear anything when i start it up since i have flowmasters but im not 100% sure if i checked the voltage the problem started a few weeks ago i just used the jumpers as a quick fix till i can really look at it. i know i didnt replace the ecm relay. what should i be reading as far as voltage?

 

You should hear the clicks of the relays when you turn the key on but not start the truck, you should also hear the fuel pump come on then shut off in about 10 seconds. Relay's should have 12v powering them.

 

Check the inertia/rollover switch which I think is located in the passenger side kick panel. It could be tripped or the switch itself could be defective.
regards
rikard

 

I just had this prob on my 90 4.9l...

i went nuts trying to isolate it. the only code was 121 which is (sensor out of range!) Really? No ****! Thanks for nothin'..lol.

I had the new pump wired to a toggle as i was only getting 9v to the pump through the new relay and new ECM through the new inertial switch and new clutch switch! Today, she wouldn't fire so I spec'd the coil and the ignition module and it was a bad module!
Changed module, threw in a new coil just because i wqas already there, Reset ECM and she purrs again without the toggle...

STILL has 121 code!