Fuel pump, or electrical problem?

[mckeig]

Hello,
Trying to resurrect the 1980 Spider (FI) after having on non-op for the last 2 years. It's cranking fine, but not firing.

I added fresh gas
I confirmed spark
I cannot hear the fuel pump come on (new fuel pump and filter were installed not long before it was parked. All worked well at that time.)
I disconnected the fuel line forward of the filter and tried cranking. No fuel came out.

I checked voltage at dual relay (green/black) and read about 12.5V when key is turned to on.
I checked voltage at power lead on fuel pump. No voltage with key in "on." With positive and negative leads on the fuel pump terminals, no voltage with key "on" or while cranking. With negative lead moved from terminal to car metal, I read no voltage with key "on" and 7.85V while cranking.

Does it seem like an electrical problem, or is the consensus that the fuel pump needs replacing? Sitting for two years may have done it in?

Thanks!

[mckeig]

One more thing. I checked impedance from the dual relay to the fuel pump, on the green/black wire, and got 48 ohms.

[spider2081]

If you have no voltage across the fuel pump terminals and then when you move the meter ground to the cars metal you measure 7.85 volts when cranking, I would suspect the fuel pump ground is disconnected in the trunk. It usually grounds to one of the drivers side tail light mounting studs. I think the small terminal on the pump is ground. try grounding it with a jumper and see if it runs while cranking.

7.8 volts sounds a little low also but I would think the pump should run even at that low a voltage.

[mckeig]

OK, I checked the ground at the tail light. It may not have been a good connection. I cleaned everything with the wire wheel on my dremmel, and now I read 7.45V across the fuel pump terminals while cranking. No pumping action, though. I'm going to call it a bad fuel pump and get one ordered. I'll post the results.

Thanks

[bradartigue]

Under 8 volts I wouldn't think it would run at all. I'd run a test wire from the battery to the positive lead and see if it runs (assuming the battery has +12V) and then figure out why you have only 7 or so at the terminal.

[mckeig]

By golly, I should have thought of that. The pump does come on with a test wire from the battery. Voltage at the battery is 13.1V. So now the question remains, why the low voltage coming from the pump power wire?

Previously I got a reading of 12.5V when I probed into the dual relay, on the side the green/black wire comes out. To my knowledge, looking at the wiring diagram, it makes no stops between there and the fuel pump. It looks like the 16A inline fuse comes before the dual relay.

Should I run a test wire from the dual relay to the pump and bypass the green/black wire?

I tried to follow the wire, but it's of course wrapped up in the harness for most of its journey.

Thanks again.

[azruss]

jumper a separate ground from the fuel pump to the chassis and see if the pump comes on. I found the taillight ground to be a problem.

[bradartigue]

By golly, I should have thought of that. The pump does come on with a test wire from the battery. Voltage at the battery is 13.1V. So now the question remains, why the low voltage coming from the pump power wire?

Previously I got a reading of 12.5V when I probed into the dual relay, on the side the green/black wire comes out. To my knowledge, looking at the wiring diagram, it makes no stops between there and the fuel pump. It looks like the 16A inline fuse comes before the dual relay.

Should I run a test wire from the dual relay to the pump and bypass the green/black wire?

I tried to follow the wire, but it's of course wrapped up in the harness for most of its journey.

Thanks again.

Run a test ground wire (w/o the test + wire). Run it from the pump negative terminal to the body. If you get 12V at this point then you've graduated in your study of "Dwight's Rule" or "It's always a bad ground." If you still get under 12V then you need to look at things like the dual relay (which controls the pump) and the wiring to and from it. Many P.O.s mess with this thing unnecessarily.

If this works then find the pump ground and clean it, get a good 12V.

[mckeig]

Run a test ground wire (w/o the test + wire). Run it from the pump negative terminal to the body. If you get 12V at this point then you've graduated in your study of "Dwight's Rule" or "It's always a bad ground." If you still get under 12V then you need to look at things like the dual relay (which controls the pump) and the wiring to and from it. Many P.O.s mess with this thing unnecessarily.

If this works then find the pump ground and clean it, get a good 12V.

OK, I'll try that next and report.

"Dwight's Rule" sound intriguing for my other problem: Turn signals blowing bulbs and/or fuses. They've never worked properly in the 9 years I've had the car.

[bradartigue]

Run a test ground wire (w/o the test + wire). Run it from the pump negative terminal to the body. If you get 12V at this point then you've graduated in your study of "Dwight's Rule" or "It's always a bad ground." If you still get under 12V then you need to look at things like the dual relay (which controls the pump) and the wiring to and from it. Many P.O.s mess with this thing unnecessarily.

If this works then find the pump ground and clean it, get a good 12V.

OK, I'll try that next and report.

"Dwight's Rule" sound intriguing for my other problem: Turn signals blowing bulbs and/or fuses. They've never worked properly in the 9 years I've had the car.

That's a short in the switch collar.

[mckeig]

That's a short in the switch collar.

That's the ignition switch on the column? Or within the turn signal switch?

[mckeig]

Run a test ground wire (w/o the test + wire). Run it from the pump negative terminal to the body. If you get 12V at this point then you've graduated in your study of "Dwight's Rule" or "It's always a bad ground." If you still get under 12V then you need to look at things like the dual relay (which controls the pump) and the wiring to and from it. Many P.O.s mess with this thing unnecessarily.

If this works then find the pump ground and clean it, get a good 12V.

We're in business!

I ran the negative test wire to the body, and got a reading of 8.5V while cranking, but I also thought I could hear it pumping. I rolled the dice and reconnected the ignition, and she immediately fired up. Ran smooth, and no white smoke in the exhaust.

I cleaned the ground connection and hooked it back up, and she started again. Checked across the pump terminals and it reads 12.1V while running.

Thanks for the pointers. Now I need to replace the heater core, which is the last thing that gave out 2 years ago, and trace the turn signal issue. I also noticed I don't have tail lights now. A project for another day.

[spider2081]

Any chance when you were cleaning the ground for the fuel pump at the drivers side tail light the tail light ground ring terminal became disconnected from ground. Usually the fuel pump and tail lights ground wires ground at the same point in the trunk.

[bradartigue]

That's a short in the switch collar.

That's the ignition switch on the column? Or within the turn signal switch?

The turn signal switch or hazard switch. Turn signal switch assembly/wiper assembly/bright light assembly is pretty rugged, hazard switches are about the junkiest part on the car. Turn signals run through the hazard switch, so...test there first.