loss of power to fuel pump

[ZacharyS]

I will start with a brief history of my relationship with this car: My 83 spider was my first car and I have had it since 1993. It was my only car for about 10 years and it served me very well until it started become less reliable. Finally I bought a new car and neglected the spider for several years. Then one day I decided to see if I could attend to some of the issues it was having on my own. At this point, it did not run at all. I had almost no previous mechanical experience, but using a shop manual and a lot of info from this site, I ended up largely taking the whole thing apart and putting it back together. Amazingly, I did get it running pretty well, but not great. This past year, it has spent several months with a mechanic that I think most Atlanta area folks are familiar with, Allan Lunsford. Allan did some very good work getting it running like new, except for one problem which I will now describe.

After driving the car for about 15 minutes or 10 miles, the operation of the fuel pump begins to fail as power to it becomes intermittent. If I keep driving, the pump will totally die. This is easy to diagnose because normally the pump is clearly audible with the engine off and the ignition switched to on. Once the car sits for 10 or 20 minutes, power is restored to the pump and it runs well again for another 5 or ten minutes. This issue is a very old one that was beginning to manifest itself way back when I used it as my only car and was one of the reasons I finally bought a new car, but it is much worse now. I know the pump itself is not the issue, since Allan just installed a new one and since the problem also predates even the previous fuel pump. I though it might have been a problem with the combination relay, but replacing that made no difference. Between myself and the work Allan has done recently, most everything else on the car has been repaired or replaced. The only other thing I can think of to try to replace is the main computer unit. Does anyone have any thoughts on this? I greatly appreciate the help!

Zach

[AriK]

A member here was having intermittent problems caused by his combination relay not being properly secured and the swinging back and forth created connection troubles. Also have a feel on its wiring and the wiring leading to the ignition switch and make sure nothing feels too hot for comfort. Perhaps this will give you a basis as a starting point.

[ZacharyS]

I cannot find any issues with electrical connections or wiring. Anybody have any other suggestions?

[spider2081]

With the engine off and ignition switch in the "run" position the fuel pump should not be running. Some previous owner/mechanic might have by passed the pump switch in the AFM or the AFM switch is not turning off the pump when the engine is not running. This issue is probably separate to the fuel pumps intermittent operation.

The dual relay has 4 power sources:
pin 88z is unfused "hot all the time" power from the brown wire connected to the battery + terminal.
pin 86c is "hot in start and run" from the ignition switch through fuse 2. This is hard to find in the wire diagrams
pin 88a is unfused "hot in start only"
pin 88y is "hot all the time" through the in-line fuel injection fuse located above and behind the fuse panel.

Any one of the above power sources can cause your problem as can the fuel pumps chassis ground that is made on the drivers side tail
light assembly mounting stud in the trunk