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)

[SirAndy]

Any other suggestion of something to check?

Double check the pump relay. Carry spares.

Check the wire on the heater lever between the seats to make sure it doesn't short out to ground. It's a very tight fit and it'll blow the fuel pump fuse ...

(IMG:style_emoticons/default/popcorn[1].gif) Andy

[markb]

Ignition switch?

[Mike Bellis]

I had the same problem with a new fuel pump. After checking everything, it was a bad, new fuel pump. Mechanical failure that acted like an intermitant power failure.

[campbellcj]

Fuse or fuse box?

[Nie Zu Alt]

Thanks for all the suggestions. I went ahead and cleaned all the terminals and fuses under the dash. I've got a number of good relays in the glove box and a good used pump in the parts stash. I took the car for a drive through the hood tonight, about an hours worth. So far so good. She ran very nicely with no hiccups. Thanks again!

[Nie Zu Alt]

Any other suggestion of something to check?

Double check the pump relay. Carry spares.

Check the wire on the heater lever between the seats to make sure it doesn't short out to ground. It's a very tight fit and it'll blow the fuel pump fuse ...

(IMG:style_emoticons/default/popcorn[1].gif) Andy

Andy, can you elaborate on this? This may be my problem as last night the heater was on - no problems. This morning the heater was off and the fuse blew in the time it took to go 2 miles.

I thought the wire on the heater lever is actually switched to ground? Sorry for being such a newbie at this.

Thanks

[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.

[Nie Zu Alt]

Update - Problem solved

After isolating the heater blower circuit, I still had the problem - blowing the fuse on the relay board.

So, I hooked up the blower circuit and disconnected the pump circuit - No problem! Blower circuit worked fine. To disconnect the pump from getting power, I did it at the relay board. I snapped the cover off of large connectors and pulled pin 13 out of T14 and pin 12 of T12 and plugged the connectors back onto the relay board.

I then put pin 13 of T14 back and tried. The pump worked and no blown fuse! I then put pin 12 of T12 back and the fuse blew. Happy day, I figured it out. Pin 12 of T12 is hot and goes to the Aux Air Valve and pin 87 of the pump relay. I chased the wire to the Aux Air Valve and found a break in the wire where it was in contact with the engine case - complete with burn marks. I repaired the break, put the pin back in the connector and it all works great! Hmmm, it even idles much better. Imagine that.

Along this journey, I also picked up a wiring diagram for the car from Prospero's Garage. Nice, in color, laminated in plastic, and easy to read. They are worth checking out.

Prospero's Garage Wiring Diagrams

Thanks for the help everybody. I'm sure I'll be back later with more questions. Here is a shot of the car - 1974 2 liter

[campbellcj]

Excellent sleuthing! It always feels good to figure out a tricky problem like that. Nice looking car, too.

[McMark]

Damn, I didn't get here in time to 'save the day' with my knowledge. Had this happen to me way back when...

Glad you got it sorted!

[Nie Zu Alt]

Yeah Mark, where were you a week ago when I needed your help? (IMG:style_emoticons/default/biggrin.gif)

It does feel good when you can track something down like this and get it fixed. Though frustrating, the knowledge gained is worth it.