924Board.org

[Portporschedon]

I was driving the 924 (1983 NA) when the engine suddenly died and then immediately started again and, at the same time, the windscreen wipers stopped and then re-started.
I continued to drive the car and the same thing happened again. this continued every few minutes while I got the car back to my house.
With the car stationary, I noticed that the temp guage needle, the fuel level needle, the tachometer needle and the volt meter needle were "flicking" at regular intervals. There was also a smell of scorching / burning.
I shut the engine down and checked for burning without success.
I switched the ignition on and heard the fuel pump start to run and then stop, then restart and stop......I do not know if this is normal or not, I normally just switch on and then crank the engine.
I swapped the fuel pump relay for a spare that I had....however that relay was bad and the fuel pump would not run at all.
I put the original back in place and the car started immediately.
While it was running I noted that the volt meter was only showing about 12.5 volts, and would suddenly "spike" across the guage to full deflection, and then immediately settle back to the 12.5 volt position.
Increasing the revs did not increase the indicated voltage.
The only work that has been done recently was a new starter motor that I fitted two days ago.

To summarise:
Engine stumbling.
Electrically driven guage needles flicking.
Volt meter showing 12 volt (engine not running)
Volt meter showing 12.5 volt (engine running) and does not increase with revs.
Volt meter needle spikes across to full deflection coinciding with the other needles flicking.
Scorching / burning smell

I think that the alternator has failed, however, if anybody has another suggestion I would be happy to receive their advice.

Don (with 2 x sick porsches )
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White 1983 924 - Renovated to near original condition and my daily driver

Dolomite 1986 924S - Coming to the end of a 4 year refurbishment.


Life is not a rehearsal

[Smoothie]

My guess would be a loose major connection somewhere - battery, starter, alternator, possibly an "H" terminal at rear of the fuse-relay panel. I'd double check all the connections you touched recently.
Intermittantly losing the connection to the battery would account for all of your symptoms including the voltage spike (I found while bench testing a 924 alternator a few years ago that taking the battery out of circuit caused the voltage to spike up over 20V). -And I believe the 924 battery wiring runs from batt-starter-alternator, so any of those connections might be loose. -And arcing at a loose connection would account for the burning smell.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Portporschedon]

Thanks Smoothie, that does make sense.
The new starter motor was a generic one and I think the main terminal was positioned slightly differently, which put the battery feed lug a bit closer to the heat shield, so arcing is a possibility. I thought the clearance was enough, I guess I was wrong .
Looks like I'm swapping the sick 924S for a sick 924 in the garage tomorrow morning.
Oh well....at least all the exhaust and heat shield bolts are greased and will come off easily.

I'll post an update to let you know how it goes.

Don
_________________
White 1983 924 - Renovated to near original condition and my daily driver

Dolomite 1986 924S - Coming to the end of a 4 year refurbishment.


Life is not a rehearsal

[Portporschedon]

Update

Thank you Smoothie...... Your diagnosis was spot on.
The lug on the battery wire connecting to the main terminal on the starter motor was arcing to the heat shield.
It had actually blown a hole through the metal, and the whole starter solenoid was covered in a white powdery residue.
I re-routed the cable back to the original routing, which enabled the connecting lug to lay in a different direction and was well clear of the heat shield.
I shouldn't work on cars when I am tired, I remember in the past routing the cable the wrong way and realising the problem, this time I didn't.

One thing that surprised me....... the car had been driven by my wife for over an hour prior to this happening, without a problem. When I took over the driving the problem manifested itself.
I can only assume that I was driving the car more "aggressively" and somehow this allowed the arrc to earth to happen.

Anyway....all is now working fine, and I have learned something.

Thank you again for your knowledge and assistance.

Regards
Don
_________________
White 1983 924 - Renovated to near original condition and my daily driver

Dolomite 1986 924S - Coming to the end of a 4 year refurbishment.


Life is not a rehearsal