Fuel Pump Wiring Issue

[mbmoehl]

My '92 C1500 Suburban doesn't trigger the fuel pump relay when the key is turned to the ON position, even for 2sec (or is it 10sec?). I've jumpered the connector (C to E) and can hear the pump running. I've also jumpered the relay at the battery and it clicks (D to F). With a test light i see there is power to the C part of the connector and to ground. I haven't put a meter on the connector D/F to see if there is power when the key is turned to ON. From looking through the wiring diagram the dark green (D) wire goes to the ECM and the F wire is essentially ground, but also seems to splice into a ground at the ECM. What i don't know is if there is an issue with the ECM or an ignition switch signal to the ECM to trigger the fp relay. What are your thoughts, what am i missing in my limited knowledge?

 

[mbmoehl]

My brother and I dug into this issue Monday and found the problem. We found two shorted wires near the electric connector attached to the fuel pump and fixed that, but it didn't solve the main issue of no fuel. So, we dropped the tank and pulled out the sending unit/pump. What we found was surprising, the hose that once connected the pump to the sending unit was completely melted away, must not have been rated for use in fuel. It was like the consistency of fresh caulk that had just skinned over. Also, the tank is rusted pretty bad inside. The plan now is to replace all of that and go from there.

You must be registered for see images attach

 

[Erik the Awful]

Unfortunately that's pretty common. I highly recommend replacing it with a Vortec fuel pump on a new TBI sending unit.

 

[Road Trip]

My brother and I dug into this issue Monday and found the problem. We found two shorted wires near the electric connector attached to the fuel pump and fixed that, but it didn't solve the main issue of no fuel. So, we dropped the tank and pulled out the sending unit/pump. What we found was surprising, the hose that once connected the pump to the sending unit was completely melted away, must not have been rated for use in fuel. It was like the consistency of fresh caulk that had just skinned over. Also, the tank is rusted pretty bad inside. The plan now is to replace all of that and go from there.

mbmoehl,

Welcome to the GMT400 forum, and what a great way to introduce yourself!

Sincere thanks for taking the time to close this repair loop & sharing that
sharp photo of the failure.

Your photo is easily worth a thousand words as a heads up of how the
outside can look road trip ready while the internals have completely
disintegrated. (!)

Given that being broken down on the side of the road today (while people are
speeding by while glued to their phones) is so unsafe, if you have brought
an old truck back to life after sitting for years and you've only looked at
the condition of the external lines, make it a priority to verify that this
potential showstopper isn't in your tank.

The difference in condition on the same part is dramatic:

You must be registered for see images attach

And if you are reading this yet can't talk yourself into dropping the tank and visually inspecting your pump
(and you drive the truck farther away from home than you are willing to walk back) ...then
at least run a fuel pressure check and react accordingly.

Again, thanks for your highly informative photo & sharing your fix.

Safe Travels --

EDIT: I just looked at your avatar, and it looks like your statue is sporting a Devo energy dome?
Man, that brings back some memories...