engine swap Fuel Gauge Issue

ZenGrimWolf · March 19, 2021

First off, hello and thank you for taking the time to read this. I will start with specs and how the truck is put together to make this easier to understand.
My truck is a 97 Chevy C1500. It originally came with a 4.3 Fuel Injected Engine. However the guy that owned it before me swapped in a 87 block style crate 350/5.7. He switched it over to carbeurated. Put a mechanical pump on it. Now when he ran the lines, he left the old fuel pump unit inside the tank. He just disconnected the power to the electric fuel pump, and the mechanical fuel pump on the block pulls its fuel THROUGH the inactive electric pump. (according to what he told me, still need to pull the tank and verify this, but wanted to get information first) So there's the basics. The issue im having is that my fuel gauge does not work. It is currently pegged about an inch or two past full.

Now, Ive been told varying things. One person tells me that the fuel sender works independent of the electric pump, and that all i need to do is replace the sender and hook up only the level wires and leave the power to the in tank pump disconnected. Another tells me that the electric pump HAS to be powered for the level sender to work, and there's now way to make it work with myy setup. That's not even including the fuel level buffer module or whatever that i just heard about today -_-

My question is this. How does the sender work in detail, and what is my best option for diagnosing and fixing my fuel gauge? Is there a way to make the fuel gauge in the dash work with the current setup, or do i need to get a separate specialized gauge and install it? Any and all help is appreciated. If y'all have any questions please do ask and i will do my best to answer them in an effort to get this issue figured out.

(Picture attached. Harness wires: Purple wire is level sender wire. Gray wire is the power to the pump. Black wire on its own is i think the ground for the pump, black wire going into plug is ground for sender, according to the wiring diagram i reviewed.)

Brian Lindsey · March 22, 2021

my suggestion would be remove pump , unhook all wire to actual pump , not sender , just pump , then place pump assembly back in tank and hook sender back up, should work if no wires were cut

ZenGrimWolf · March 23, 2021

20 hours ago, Brian Lindsey said:

my suggestion would be remove pump , unhook all wire to actual pump , not sender , just pump , then place pump assembly back in tank and hook sender back up, should work if no wires were cut

i appreciate that. i have actually done this (there is no pump at all in the assembly the previous owner setup, just a hose and sock strainer) and completely disconnected the pump while leaving the sender connected. I have confirmed resistance readings within spec at the connector, so i know the signal is being sent. But the fuel gauge wasn't working still. So i traced the wires back to the buffer module (the thing that keeps your gauge from bouncing) and verified that the signal is reaching the module and has the correct ohm readings. i then verified that the module had power, reference and was sending an output signal to the cluster. Thats all within spec so im beginning to think i may have a short/break in the output lead wire going from the buffer module to the cluster, somewhere behind the dash(yaaaay), causing the gauge to act the way it does. Every thing else seems to be functioning correctly, and the gauge is good too (borrowed a verified good cluster with working gas gauge from another truck and installed it, gauge did the exact same thing as soon as i turned the key on) so the only thing i HAVENT tested is the harness wiring going from the buffer to the gauge. Looks like im gonna be having some fun!

I appreciate the help already given and im open to any suggestions anyone else may have. Thank you