Lift pump wont run

[SBashaw]

My nephew call me with a question on is 03 that i could not answer, hoping to get a little help here.
his all original truck started running rough with 255,000 miles on it, so he changed the injectors and crossover tubes, and FCA. Now the LP wont run when he turns the key on. if he pulls the connection and jumpers the pump to the battery it runs fine. he has checked the connection with the key on and is showing 11.75 VDC to the pump? truck turns over good. any ideas? thanks in advance.

 

[TRAMPLINEMAN]

Is there a fuse or relay that could have gone bad?

 

[PWong]

Now the LP wont run when he turns the key on. if he pulls the connection and jumpers the pump to the battery it runs fine. he has checked the connection with the key on and is showing 11.75 VDC to the pump?

With the pump connected, check the voltage again between the two wires at the connector when key on.
Since it ran with jumped power, bet it's the fuel pump relay or the wire between relay power output to pump.

 

[SBashaw]

With the pump connected, check the voltage again between the two wires at the connector when key on.
Since it ran with jumped power, bet it's the fuel pump relay or the wire between relay power output to pump.

Thanks for the quick reply's, I do believe he has checked the fuse , I will tell him about the relay and to recheck voltage when hooked up. let you know what happens.........

 

[Missouri Mule]

Probably the relay. But did he run just positive wire or positive and ground?

 

[SBashaw]

Talked to him today, he says there is no fuse or relay on an 03, wire to pump comes straight from EMC? Anyone have a wiring schematic for an 03 SO?