Intermittent Fuel Pump - Anything else to check? Options

[Nie Zu Alt]

Group,

I think I may have fixed the fuel pump problem on my '74 2.0 liter, but I'm looking for suggestions of anything else to check. My pump is realitively new, 4 years old, and is located in the spare tire area in the front trunk. The problem is that power to the pump has been intermittent, cutting off when least expected - like in the middle of a busy intersection. I decided to dig in and fix it since it seems like an electrical issue, not the pump.

So, I...

1. Cleaned all pins and sockets on the relay board and connectors with contact cleaner and pipe cleaners.

2. Used di-electric grease on all pins and sockets.

3. Respliced wires by fuel pump connector. (found one wire joint corroded and iffy looking)

4. Respliced wires where fuel pump use to be under engine.

5. Checked continuity of wires between engine bay and fuel pump in the front - Good, regardless of tugging and pulling of wires. The wires were run through the tunnel.

6. Cleaned ground points under relay board and terminals on on case.

After that, it started right up and seemed fine. I took it for a test drive and it died 100 feet from the house. Same problem - No electricity to pump.

Turned out to be the fuse on the relay board blew. Replaced it with a new 25 amp fuse. (So why did the 16 amp fuse work for the past 2 years? Luck? Corrosion/bad joint prevented a full load on circuit? Dumb me didn't notice this earlier.)

Seems to run fine now.....so far. Will test drive around the neighborhood more tonight. Any other suggestion of something to check? (IMG:style_emoticons/default/idea.gif)

[swl]

I think you're right about the switch going to ground. Also the coil side of the relay (pin 85) is not fed from that fuse. The over current is happening on the switched side (pin 30).

I think Andy is on the right track though. It sounds like the fault might be over in the fan delivery cct or possibly in the rear window heater cct if you have one of them. All of them get their power from that fuse.

Shorts, or worse intermittent shorts are really hard to find. You can try metering from pin 87 to ground to see what sort of load is on each of the three ccts. I can't tell you what normal is but if nothing jumps out at you (hard short) I could take some measurements to compare to.

If nothing jumps out at you you could also try pulling the heater and defrost relays and just see if the fuel pump survives on it's own. If it does add back the other two circuits one at a time.