Fuel pump charge

[Ellie]

Hi team, hoping someone more electrically minded can help with this question. When I turn the key, she cranks and starts, runs for 5 seconds then dies. I've read a few posts where this symptom has occurred and note it could be a variety of things but I've started with the fuel pump.

Using a multimeter I've checked there is power from the ignition to the wires at the pump when unconnected, the full 12+ volts comes up. However as soon as I connect the wires to the pump, the volts drop to like 2 or 3. And this is not while cranking, its just with the ignition turned on.

So the question is, is this normal? presuming it's not normal, are there any suggestions as to what may be causing the power fade?

Many thanks
Mike

[spider2081]

the volts drop to like 2 or 3. And this is not while cranking, its just with the ignition turned on.

First a 1982 Spider should be fuel injected. Fiat/Bosch wired the fuel pump with a safety feature. With the ignition switch in the "run" position power for the fuel pump passes through a switch in the Air flow Meter. The engine needs to be running for the switch to be closed thus supplying voltage to the pump. Your pump should not have voltage measured between the green/black and white/black wires when the ignition switch is in the "run" position. Possible the cars wiring has been modified by a previous owner.
I would unplug the Air flow Meter and see if you still measure voltage at the fuel pump when the AFM is unplugged.

The fuel pump should have voltage when the ignition switch is in the "start" position. To check this I disconnect the single bullet connector in the red wire located near the engine mount behind the alternator. This disconnects the starter solenoid energize wire from the ignition switch.

[Ellie]

Thanks Spider2081, yes it is Fi as you say. So that means when the two wires are connected to the pump and I turn the ignition to run, it is correct that I have no or next to no voltage reading. I think that's a good thing. I will need to check the reading with the ignition on start now. Good tip about disconnecting the starter solenoid too.

Is it weird that when the wires are loose, as in not connected to the pump, the green/black and white/black wires show 12V?

[spider2081]

Is it weird that when the wires are loose, as in not connected to the pump, the green/black and white/black wires show 12V?

Yes that is strange. The taillights and the fuel pump share the same ground point in the trunk. Factory used one of the left side taillight mounting studs for the ground point. If this is not making a solid ground the lighting circuit could be back feeding the fuel pump. Have you measured the fuel pump wires voltage to ground? There should be no voltage on either wire with the ignition switch off or in run positions.

The fact the voltage reading on the disconnected wires is 12 volts but it drops to 2-3 volts when the wires are connected could indicate a poor connection some place in the circuit So there could be more than one issue contributing to what appears as a single problem.

[redcars]

The fact that it starts means that the pump is good. The fact that it then stops could mean that the switch in the AFM is bad. Also as said check your grounds. A lot of electrical problems in old cars are ground problems.

[Ellie]

The voltage testing so far has been interesting. I tested the power and ground at the pump when connected to the pump. With ignition off voltage was zero, when switched to start a very light reading of .3, so some power trickling in, but I’d call that pretty much zero. Then when switched to run, while it was cranking and idling for the 5 seconds, the voltage was 6.5.. I then left the ignition on start and manually closed the airflow switch…with a stick. Fuel pump clicked and the voltage again read 6.5. I’m guessing not enough voltage to keep the pump operational. interestingly when I disconnected the wires form the pump and did the same process testing the ends of the wires at the pump (but not connected) the voltage read the full 12.6. So there is power running to the pump, just not when connected. Could the pump itself be shorting or some other magical electrical disfunctionality?

[spider2081]

the voltage readings you state are indicators of a bad connection or dead battery.
I assume if you state the engine cranks over that the battery is not the issue.
Have you measured the voltage on the green/black wire at the fuel pump to chassis ground. If the voltage is still too low the problem is in the pumps power circuit If the voltage is battery voltage then the problem is in the ground wire.
I like to disconnect the red single bullet connector behind the alternator close to the engine mount. This is the wire from the ignition switch to the starter solenoid. Disconnecting it allows turning the ignition switch to "start" and not having the engine cranking. Then check for voltage at the fuel pump with the key in the "start" position. This power path does not go through the dual relay and airflow meter. If measuring the voltage on the green/black wire to ground (pump connected) with the ignition switch in the "start" position, I would check voltage into and out of the ignition switch. Both the grown and the Black wires in the ignition switch connector bring batter power to the ignition switch. The brown wire switches to the red wire when the ignition switch is in the "start" position.
The fact that the voltage reading at the pump changes when you move the flap in the AFM points toward a bad connection at the dual relay.
If you have a helper jiggle the wires in the dual relay while looking at the voltmeter connected to the pump wires.

[spider2081]

the voltage readings you state are indicators of a bad connection or dead battery.
I assume if you state the engine cranks over that the battery is not the issue.
Have you measured the voltage on the green/black wire at the fuel pump to chassis ground. If the voltage is still too low the problem is in the pumps power circuit If the voltage is battery voltage then the problem is in the ground wire.
I like to disconnect the red single bullet connector behind the alternator close to the engine mount. This is the wire from the ignition switch to the starter solenoid. Disconnecting it allows turning the ignition switch to "start" and not having the engine cranking. Then check for voltage at the fuel pump with the key in the "start" position. This power path does not go through the dual relay and airflow meter. If measuring the voltage on the green/black wire to ground (pump connected) with the ignition switch in the "start" position, I would check voltage into and out of the ignition switch. Both the grown and the Black wires in the ignition switch connector bring batter power to the ignition switch. The brown wire switches to the red wire when the ignition switch is in the "start" position.
The fact that the voltage reading at the pump changes when you move the flap in the AFM points toward a bad connection at the dual relay.
If you have a helper jiggle the wires in the dual relay while looking at the voltmeter connected to the pump wires.

Mirafiori.com has a library for members that contains loads of reference material and wire diagrams. Joining is free.
Fiat publication "Spider 2000 Electrical Diagnostic Manual 1980-1981" might contain information useful to you.

[Ellie]

Hey thanks for all that, I have a couple of questions though. I can’t find that bullet connector behind the alternator which is a worry but I’ll keep looking, surely it can’t be too hidden I thought that the airflow sensor was supposed to deliver power to the pump when open? Otherwise I’ll keep checking some of those other things you suggest, your wisdom is much appreciated.

[spider2081]

I can’t find that bullet connector behind the alternator

I believe all later model Spiders have 2 wires with single bullet connectors. One is brown and the other is red. Both originate at the starter solenoid and are in a plastic sleeve. In the area above the cross member behind the alternator the single black bullet connectors are located. Pull the red wire connector apart. That will interrupt power to the starter solenoid in the start position of the ignition switch.

I thought that the airflow sensor was supposed to deliver power to the pump when open?
Yes that is correct. The power supplied to the fuel pump relay from the "start position of the ignition switch is a second path. It insures the fuel pump is running when the engine is cranking and the the AFM flap is not necessarily open. Either source the flap switch or the ignition switch energizes the fuel pump relay in the dual relay.

[redcars]

Your voltage readings could also indicate a bad grounds.

[Ellie]

Thanks for the suggestions which I will work through next weekend. I think I’ve found the connector behind the alternator and the ground connection in the boot which I’ll clean up. Here’s a thought, what would happen If I hot wire the pump direct to a separate battery? Will something blow up? Will not using the green black and white black wires not complete a circuit and the car won’t start anyway? So many questions…

[spider2081]

would happen If I hot wire the pump direct to a separate

That should work. The fuel pump should run and nothing bad should happen to the car.
you could jump the cars battery direct the fuel pups + terminal with the same results.

[Ellie]

Happy Days. I hot wired the pump to a spare battery and immediately heard the pump humming, which is something it wasn’t doing before. I was almost cried with joy, turned the key and she burst into life. After a few minutes I disconnected the spare battery and she kept running on her own. Left to idle for about 5 minutes the turned off. Now just starts up as if nothing was ever wrong.

It’s the first day of Spring here in Australia and I reckon she was just refusing to leave the garage while it was still Winter. Hahaha, love this car