Hi everyone i have a major issue with my 2000 Chevy Blazer well my fuel gauge quite working. A month ago i pulled the engine out to rebuilt it. I also replaced the fuel line from the motor to the filter. while the engine was out. I also pulled the fuel relay to set the timing. Well after getting it all back together i Noticed my fuel gauge wasn't working it went to full and immediately went to empty and ever sense its be pegged on empty. I changed the Sending unit and plug along with Evap vent solenoid. i am getting 5 volts on the purple wire and the black/ white wire getting noting put if i touch black/white wire with the the black wire my fuel gauge works but will throw and engine code for fuel tank pressure sensor. I was told the black/ white wire is a hot/ ground wire. How do i test that wire to see if its a broken wire. Or even what to look for.
I'm hoping someone can help me with this. Thanks

 

There are two wires for the fuel level sender: purple for the high side and blk/wht for the signal ground. The blk/wht signal ground leaves the pump assembly and heads to splice block 422/423 on the rear frame where it is joined with the signal ground from the fuel tank pressure sensor which also uses a blk/wht wire. From there another blk/wht wire leaves the splice block on its way to the PCM. Along the way it turns into a blk wire and enters the PCM on pin 8 as a low reference/signal ground provided by the PCM. Back at the splice block a completely different node that is not mixed with this sender signal ground that is the ground side of the fuel pump on black which leaves the splice block as black and gets connected to chassis ground via ground point G402 at the rear cross member.

The fuel tank pressure sender could perturb this shared ground as could any wiring as could the PCM no longer providing a proper signal ground.

George

 

George LG if It wasn't for you i would of never found the broken wire by the cross member Thank You so much i owe you one thank you again.