924Board.org

[nuno almeida]

Hello guys,
The car has been sitting for about three years. The last time it was driven, everything shut off while driving, as if the battery had died. Since then, it's been parked in a garage. Now that I have some time to fix it, I'm running into a few issues. The fuel pump relay isn’t clicking, and the fuel pump isn’t priming.

I ordered a new ignition module from eBay because the old one smelled burnt, so I replaced it—but that didn’t solve the problem. Then I started suspecting a ground issue (which I still think it might be). I also tried a new relay, but that didn’t work either.

I tested connecting the 31b terminal on the fuel pump relay directly to the ignition module, and the relay clicked and primed—but only when I touched the two wires together. It doesn’t prime via the ignition key, which I found odd. I’m not sure if the issue lies there, because I don’t know exactly where the ignition module wires go.

I also tested the ignition coil: I got 10V on the positive and -0.13V on the negative. When I connect a wire from the negative terminal to ground, the relay clicks and the fuel pump turns on. (Is that normal? It seemed odd.)

Also, fuse number 6 (hazard lights) keeps shorting—it blows every 5 minutes. When I switch on the hazard lights, all the dashboard gauges start trembling.

I have some photos and a video—where can I upload them?

[924RACR]

The fuel pump priming when you ground the one ignition terminal makes sense to me; that voltage drop mimics the coil being triggered, which is the signal the pump relay is looking for to run.

So in an unexpected way, this would SEEM to indicate that your circuit to trigger the pump relay with ignition functioning is good; there is a valid good connection from the coil to the relay, and the relay will respond OK if it sees the ignition signal.

Which makes me think the issue is entirely on your ignition side, not the fuel pump, relay, and wiring.

To remove the pump relay and wiring from the question while you are debugging, you can of course short the relay - but once you get the ignition working, you probably won't need that.

The issues you mention with the hazard lights maybe also supports that you have wiring or other electrical issues. For one, I would inspect and clean the grounds, both under the dash (behind the fusebox) and up by the ignition box - if you haven't already?

Time to start at the beginning with checking the ignition. I'm a little unsure of the exact steps since you have a late EU car... but the most basic, if you connect a spark plug lead to a spare plug and touch it to ground (like on the intake), do you get a spark? I'm guessing no...

After that, you really need to work step-by-step through the diagnostics, the factory manual is quite good in this regard... hoping you have one or access to a copy?

Re: posting pics/video - we don't have any such facility directly on this board, so you need to post them somewhere else and link...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[nuno almeida]

The connection between the fuel pump and the relay is fine because when I bridge the relay, the fuel pump primes—it just doesn’t prime with the ignition as it’s supposed to.

I’ve already checked all the ground points. The one behind the fusebox—what is it supposed to ground? They had a bit of corrosion; I cleaned the connectors (photo 1) where the terminals plug in. I haven’t cleaned the terminals themselves yet because I was testing other things, but I believe the other ground points are fine.

I’ll try the spark plug lead test over the weekend.

And no, I don’t have the factory manual—I’ll see if I can find it online.


https://drive.google.com/file/d/1nkOwXDt5j4samVM53CiHctR5OBEk1vVv/view?usp=sharing (this happens when i turn the hazard lights on)

https://drive.google.com/file/d/1Nsz82SEqTA9c6lx6aS1zGZ7ThX7nq6HL/view?usp=sharing

https://drive.google.com/file/d/1OixCM0F6dvpqhJXUOVPbubvhTP2oCdiV/view?usp=sharing

PHOTO 1- https://drive.google.com/file/d/171-luDk7WHE2PgRKC2xpzo2VwC5BEpd6/view?usp=sharing

Thank you for the help!!

[924RACR]

The grounds behind the fusebox ground the dash instruments, control boxes, so many things...

I have been known to add more grounding wires for the instruments and dash lights, because Porsche under-specced the wiring in this area it seems...

Watching that video, I would be thinking that yes you still have some weak grounds in the dash... maybe some liquid metal cleaner/polish or something like spray contact cleaner can help you clean the terminals that go on those ground points...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[nuno almeida]

I'll try to clean them over the weekend. Do you think this ground issue could also be what's preventing the relay from clicking with the ignition?

[924RACR]

[nuno almeida]

I'll try to do it over the weekend and will give you an update if it worked.

thank you