924Board.org

[Aussie931]

Just wondering if anyone has had any issues with their ignition dropping out.

For the last 12 months or so, my ignition has been cutting out at very random intervals - I can drive for weeks without it happening once whilst at other times it will cut out half a dozen times during a 10k trip to work.

Today it died all together and the car won't re-start. I am fairly convinced that it is an ignition and not fuel problem as, when the problem occured before the car died, the tacho would drop to zero for the second or two that the engine would stop, and then would suddenly come back to life - there was no slow grind to a stop or stuttering.

So far I have replaced the ignition switch and fuel pump relay without success. My next step is to look for a replacement CDI unit.
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1979 Series 1 924 turbo

[ideola]

What year is your 931?
{EDIT}
D'oh. See it now in your signature.

Hmm. My first inclination would be the ignition switch, but if you've already replaced that....

One thing I would do immediately is to eliminate the overboost switch as a possible culprit. When these fail, they usually fail to the open circuit mode, meaning that the fuel pump relay is not getting power. The failure could either be in the switch itself, or more likely, in the ground wire that is connected to it. The spade connector may have worked its way loose, or the wire may be frayed or completely broken off. For the short term, what you can do is remove the wire from the switch and connect it directly to ground (a bolt on the intake manifold or head will do just fine). Grounding this line will eliminate the overboost switch as a possible variable. The overboost switch is screwed into the front edge of the solid charge tube just before the throttle body.

If it still doesn't start, your problem is elsewhere. Leave the overboost switch OUT of the circuit for now (sometimes there are multiple problems going on at the same time...). In my experience, the CDI units rarely go bad, but it's not inconceivable. I would do a test to confirm whether you're getting spark at the coil. Take the main coil lead off of the distributor cap and use a spark tester to confirm that your getting spark at the end of that lead. If you are, the problem is down stream of the coil (distributor, rotor, cap). If you're not, the problem is upstream of the coil (coil itself, main coil lead to cap, CDI, bad ground or positive connection at the battery, etc.). Make sure to check and double check the battery connections. My experience is that the CDI ignition is somewhat finnicky about solid ground connections. I had a similar problem on my 81 NA (uses a very similar CDI unit), and it turned out I had forgotten to fully tighten the ground connection after doing some other work on the car.

HTH.
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erstwhile owner of just about every 924 variant ever made

[Smoothie]

Also possible flakey rev-limiting rotor if you have one.
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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

[Aussie931]

Thanks for the tips.
I took the CDI unit out this morning, gave it a few hits with a screwdriver and hooked it back up and the car turned over just fine. Maybe I managed to establish a more solid ground connection when I reinstalled it?
I am very doubtful that this will be an enduring solution, however, will see how it goes.
thanks
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1979 Series 1 924 turbo

[stevekat]

Sounds like you discovered it is the CDI or its connector. However if it reoccurs, I'd also remove the fuel pump relay and jumper the proper pins on the relay panel, with a fused, switched bypass, even though you don't suspect this, just to eliminate the fuel pump relay (and its other internal workings) as a possible culprit.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[Aussie931]

Just wanted to let you know that I managed to work out the cause of my ignition cutting out. Whilst parked on the side of the parkway on my way home from work last night as a result of the ignition cutting out again, I pulled the relay panel out and discovered that the ground wire to the fuel pump relay was loose in the back of the panel. Needless to say that after making sure that it was inserted firmly into the back of the panel, the car turned over and hasn't missed a beat since.
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1979 Series 1 924 turbo

[stevekat]

Good find.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.