NZKnight

I had an odd issue where the fuel pump suddenly stopped running on my 83 CFI Trans Am. The car is fitted an auto alarm and immobilizer - which is important to the story.
On the day it failed, I disarmed the car alarm, the immobilizer disengaged and I went to start it. The engine would crank but not start. I then noticed that I couldn't hear the fuel pump priming when I turned the car on. I unplugged the fuel pump and using a digital multi meter I found there was 12v present when the car was turned on and this would shut off after a few seconds to allow the system to prime. This appeared to confirm the ECM and fuel relay was working correctly. I checked the plug and reconnected. Tried to start the car, same issue - the pump was not running. Incidentally I replaced the pump about 3 months prior so was very disappointed when it appeared to have failed.

I did the usual checks, the fuse was intact, the immobilizer was working as I could crank the engine and I appeared to have 12v at the pump. I then disconnected and fed the pump with 12v from another battery and it worked!
I then connected a 12v lamp across the car connector where I was getting the 12v for the pump and the lamp did not illuminate. I used an analogue meter and found there was no 12v on the connector and the digital meter was picking up some ghost reading. Really odd all the same. I check the grounds and they were OK. I then tried to feed the pump via the ALDL connector - pin G. The pump wouldn't run. I then surmised I had a 'hole' in the wire.
This got me thinking to how the immobilizer was wired into the car and I knew it included a fuel pump cut off. Under the trim beside the driver seat I found the problem! The alarm installer and cut the tan fuel pump wire and connected it through the immobilizer. The connections were taped up so after removing the tape I discovered the installer had wrapped the copper wires for the immobilizer around the aluminum core fuel pump wire. They had tried to solder this but the solder won't take to aluminum. Over time there had been a build up of corrosion in joint to the point it lost connection or the ability to pass sufficient current to run the pump. The digital meter was correct, there was 12v there but had no grunt! Redid the connection with crimps and the pump worked again as designed.

Hopefully this story might help someone else. BTW - it took me a week of frustration to find this and an unnecessary purchase of a new pump.

SbFormula

Thanks for the write-up

Yes you can get 12V but when load is applied, current may drop if connections are bad. Not uncommon.

Cheers!

72buickgs

Great detective work.