Fuel Pump Troubleshooting, I'm stumped Options

[ThinAir]

Trying to get my car on the road for Red Rock Classic. It's not looking good.

I had an intermittent problem with the fuel pump not running, which at the moment seems to be no longer intermittent. I've successfully tested the pump by connecting it to a battery charger.

I've followed the steps in the two fuel pump diagnostic documents at Jeff Bowlsby's site (http://bowlsby.net/914/Classic/zTN_FI_FPChecklist.pdf and http://bowlsby.net/914/Classic/zTN_FI_FPChecklist2.pdf). They both fail at the point where it says I should wrap a wire around pin 87 and reinsert the relay. I get no power on the wire. Following the steps in the Brad Anders document, I don't have 12V on pin 86 and when I test pin 8 on the plug I have power so that means I have a faulty relay board trace.

My board was rebuilt last year by a member here who has a great reputation so I don't have any reason to doubt my relay board. I have also tested with 2 other relay boards as well as multiple relays - all with the same result.

It just doesn't make sense to me that 3 boards could all have the same issue. I'm stumped. Can anyone provide some additional things to check?

[TravisNeff]

I would also suspect the relay board. When you turn the key you should have power to the pump for a second or two. Then only when cranking and the ECU needs to be connected. Maybe a loose finger on the ecu plug??

[Spoke]

You can isolate the fuel pump drive circuitry from the FI ECU. I assume you have fuel injection and the OEM FI ECU.

Here's a way to check the fuel pump drive circuitry:

1) Pull the FI ECU plug from the relay board connector.

2) Pull the +12V wire from the Positive + connection on the ignition coil. This is just to keep the coil/points/Pertronix/electronic ignition from overheating while you do the test.

3) With a separate wire with female spade connector, connect to pin III on the relay board FI connector and connect the other end of the wire to chassis ground. This will turn the fuel pump on full time with ignition on.

4) Turn ignition switch to ON; don't start the engine. You should hear the fuel pump run full time.

With this setup, you can check the fuel pump control circuitry without interference from the FI ECU.

[ThinAir]

Thanks, Spoke. I'll give that a try in the morning.

I should have mentioned, here's my setup:
1973 2.0L with stock FI
Fuel pump moved to the front and wired through center console by extending the factory wires.
I don't remember the brand, but the pump is one with the inlet/outlet on either end.

I tested the pump and wiring by connecting my battery charger directly to the pump and at the connection to the original wires.

I'll report back tomorrow.

[ThinAir]

Grounding pin III does indeed cause the pump to run.

Using some tips from some other threads, I checked the voltage on Pin 14 with key off and pin 8 on the connector with key on. In both cases I got 12 V as I should.

I also checked continuity from pin 10 on the board to pin 86 on the FP relay socket, but got no continuity there on any of the boards which I have.

It still seems odd that I could have 3 bad relay boards. I've attached an image that I found in one of the threads. I've added my own notes in green for the locations of pins 10 & 86. Assuming that I've got that right, is the lack of continuity the problems with my boards?

[rhodyguy]

Can you use the carb jumper wire trick to power the pump for testing? It would run continuously when the key was turned on.

[ThinAir]

Can you use the carb jumper wire trick to power the pump for testing? It would run continuously when the key was turned on.

I'm not familiar that trick (at least by name). Is it something different from grounding pin III, which also makes the pump run continuously?

[SirAndy]

Can you use the carb jumper wire trick to power the pump for testing? It would run continuously when the key was turned on.

I'm not familiar that trick (at least by name). Is it something different from grounding pin III, which also makes the pump run continuously?

I'm pretty sure those are the same thing ...
(IMG:style_emoticons/default/idea.gif)

[SirAndy]

Is your fuel pump fuse OK? (91) in the pic below.

Also note that pin III seems to be directly connected to 86 on the fuel pump relay.
(IMG:style_emoticons/default/idea.gif)

[ThinAir]

Is your fuel pump fuse OK? (91) in the pic below.

Also note that pin III seems to be directly connected to 86 on the fuel pump relay.
(IMG:style_emoticons/default/idea.gif)

Yes. I have continuity between pin III and pin 86. The fuel pump fuse has been confirmed to be good.

[dr914@autoatlanta.com]

no all three cannot be bad and relay boards rarely fail. make sure you have power to the fuse on both sides of the holder

Unplug and plug the power relay with the key on the coil wire to the condenser unplugged and with two good known relays (you can test them in the rear relay slot for the heater blower motor. Each time the main fuel injection power relay is plugged in (second from the front, front most is the rear window defrost relay slot) two injectors should click and the fuel pump run momentarily and stop. If the two injectors do not click, check the ground leads at the back of the block, if they do, then pop off the front harness cover cap and put a test light to the first left front pin the black with the red and repeat the plugging and unplugging. If the test light goes on and then off for a moment, the fuel pump wiring or plug or ground lead is faulty

Trying to get my car on the road for Red Rock Classic. It's not looking good.

I had an intermittent problem with the fuel pump not running, which at the moment seems to be no longer intermittent. I've successfully tested the pump by connecting it to a battery charger.

I've followed the steps in the two fuel pump diagnostic documents at Jeff Bowlsby's site (http://bowlsby.net/914/Classic/zTN_FI_FPChecklist.pdf and http://bowlsby.net/914/Classic/zTN_FI_FPChecklist2.pdf). They both fail at the point where it says I should wrap a wire around pin 87 and reinsert the relay. I get no power on the wire. Following the steps in the Brad Anders document, I don't have 12V on pin 86 and when I test pin 8 on the plug I have power so that means I have a faulty relay board trace.

My board was rebuilt last year by a member here who has a great reputation so I don't have any reason to doubt my relay board. I have also tested with 2 other relay boards as well as multiple relays - all with the same result.

It just doesn't make sense to me that 3 boards could all have the same issue. I'm stumped. Can anyone provide some additional things to check?

[ThinAir]

It works again!

After reviewing the diagram, I decided to check continuity between pin 10 and pin 86 on the Power Supply relay (75). It checked out.

At this point I plugged in all the relays and the 14 pin connector and tried it again. Much to my surprise, the pump ran like it was supposed to and the car started and ran just fine.

I'm thinking that I just had a loose connection all along. I'm suspecting that it was something in the 14 pin connector, but I really don't know how to pin that down.

Thanks for all the helpful hints. Time to drive it and see if it continues to behave. If it does, then it will be at Red Rocks this weekend!

[ThinAir]

(IMG:style_emoticons/default/driving.gif) WooHoo!!!!

Just got back from and extensive test drive. Everything worked wonderfully.

I haven't been able to drive this car since March. To hear again the note of the exhaust and the rumble of the engine behind me was wonderful. Feeling the acceleration and taking curves at speed - WOW. I'd forgotten just how sweet this is.

Red Rock Classic 2019 - here we come!

[jim_hoyland]

A spare pump is cheap insurance... (IMG:style_emoticons/default/smile.gif)

[SirAndy]

Red Rock Classic 2019 - here we come!

Pack spare relays and make a emergency jumper wire, just in case ...
(IMG:style_emoticons/default/biggrin.gif)

[Spoke]

It works again!...I'm thinking that I just had a loose connection all along.

(IMG:style_emoticons/default/beerchug.gif)

Good to hear. The unplug-then-plug on connectors is a very common fix with older electrical equipment. Connector contacts oxidize with age and moisture and the unplug-then-plug scrapes the oxidation away to make better contact.

It is a warning sign that some preventative maintenance on the plugs and sockets is warranted. Get some kind of small wire brush and clean the contact surfaces of the plugs and sockets for robust connection.