1988 930 shuts off and no restart until cold

[Tuttobenne]

A friend's 930 recently has been giving him trouble. On a recent drive his car simply shut off and wouldn't restart for another 20 minutes. We were on a busy road and I know little about Porsches so I couldn't really help other than to stand by until it finally restarted and I followed him home.

I hadn't realized he has been struggling with this problem for a while; he felt he had fuel pump problems, so I offered to help. Here is what I have found so far:

1. When cold, the car fired up and ran fine in his garage for around 30 minutes of idling. It simply shut off on its own though and would not restart. After fiddling around for quite some time I came away with more questions than answers so I did some reading online.

2. Returned to the car. Disconnected the connector on the front of the airflow meter. Turned on the ignition (did not crank the motor) and the both pumps ran fine.

3. Turned the ignition off and reconnected the connector on the airflow meter. Depressed the plate slightly with the ignition on and once again, the pumps ran. Started the car and let it run for a half hour before the pizza arrived. Shut it off and tried to restart and it fired up fine.

4. After lunch went back to start it and it just cranked. Took the connector off again and the pumps both came on fine.

5. Pulled the coil wire at the coil and held it close enough to the tower that a spark should jump. My buddy turned the key on and as soon as he did, a spark jumped across the gap into the coil tower. But once he started cranking, no spark.

I can understand the pumps not running until the airflow plate moves sufficiently but why no spark? Is there some logic in the circuit that inhibits ignition under certain conditions? What should I check?

I was thinking Crankshaft position sensor but then I read the distributor is relatively simple with a magnetic pickup triggering the Ignition Module. He has a partial Workshop Manual which stops in the middle of section 28, which is Ignition. There are some tests I can do and next time at the car I will do them. But I don't think I have enough information to rule the module in or out because the manual stops in the midst of checking it. Any thoughts?

Of course, if anyone has a better track for me to chase down, I am good with that too. Gotta say that its nice working with an engine that is all right there pretty much in front of you. And the heat is appreciated too. Thanks in advance.

[RarlyL8]

Oh there are a lot of threads on this topic. Relays, CDI, green wire, coil, coil wire, distributor, all or any could be the culprit. Because it is ignition related you can check at the beginning of the daisy chain and see how far you get until no power. Intermittent issues can be hard to trace but if it's heat related you can test things during that event.

[T77911S]

coil and CD unit are the usual top picks for heat related no start/no run.

I would start with the coil since it is cheap.
you can listen to the CD unit with the key on.
if it makes NO sound, it is bad, if does make a whine, it "could" be good.
take a listen to it when it runs so you know what to listen for.

if you buy a coil and that is not it its good to carry a spare. it saved me. I also carry a spare CD unit

[boosted79]

"if it makes NO sound, it is bad, if does make a whine, it "could" be good."

Not all of them whine, the one on my '79 never did and it worked fine until I put the programmable MSD on. There was thread on the tech forum about this.

[Tuttobenne]

Originally Posted by T77911S

coil and CD unit are the usual top picks for heat related no start/no run.

if you buy a coil and that is not it its good to carry a spare. it saved me. I also carry a spare CD unit

Thanks for your post. This is the kind of experience-based info I was looking for. I'll test the coil and if that is good, do my best to test the distributor per the WSM. That CDI box sure seems expensive so it would be nice to rig up a bench test for it.

[ETA930]

Few years back, my 87 had similar issues, get some heat in it and just stumble. Here's the kicker, the only way it would act up was under a somewhat of a lug in a gear, never under a pressure/boost situation. 12 years of driving, this thing never let me down sans 1 yellow overboost relay, which I knew from the past, would get me eventually.

When it started acting up, I had visions of everything that R8 mentions going wrong with my turbo, here we go. Being a neanderthal mechanic that I am, I did my due diligence and wiggled the red and black relays in the front, checked fuses for and aft, cdi whined like always, pumps good, coil new, boost held, ignition components proper. Eventually it was taken to my wrench, judging by the bill it wasn't much.

So, what did he do? TTBOMK, he adjusted the air/fuel mix. I tried to pry more out of him, but I can see I would have a better chance finding out where my buddy gets his morrels. One thing to note, if my car would kill, I could push the clutch in while moving, recycle the ignition switch, and it always would start...albeit with a lean backfire (sometimes). My point is, if I were a betting man, I would have bet the farm on an electrical/relay issue, because of the heat issue...never bet against a 930!

[356911930]

Some guys would carry an small ice chest with a bag of ice in it and when the car dies would put the bag of ice on the CDI box to cool it down. If car started then they would have the CDI rebuilt.

Rahl

[Pfan]

Had a very similar problem.....occasionally would die when warm and had to wait about 20 minutes before it would start. Tried everything but because it was so intermittent the problem was hard to diagnose. Finally decided to just have the CDI rebuilt. The Calif rebuilder is the guy to use...he gave me a modified loaner that had a micro lite that indicated power. He tested my old one ..it was fine initially....but left it on test overnite and it failed finally. Less than a $300 gamble and it paid off. I would suggest this before going thru heroics testing everything.

[T77911S]

Originally Posted by boosted79

"if it makes NO sound, it is bad, if does make a whine, it "could" be good."

Not all of them whine, the one on my '79 never did and it worked fine until I put the programmable MSD on. There was thread on the tech forum about this.

that's why I said check it when it is running and working,

[Noah930]

I had a similar hot-start problem. Well, not exactly the same, as my car didn't shut off by itself. But rather, if the motor was hot, it would not restart. Finally (after everything else mentioned above checked out as OK) chased it down to the little black box under the driver's seat. So if you've exhausted all other options, don't forget to look there.

[Tuttobenne]

Just to close out this data point, we got a repaired CDI box from ECU Doctors in FL and the correct Bosch coil. This solved the shutting down issue.

The day I installed the box and coil for my buddy he blipped the throttle a couple of times and I was aghast at the clanking noise coming from the engine. He told me "it always did that". Well long story short, I found some threads on the seals in the blow off valve and replaced them. Problem solved. Thanks guys for all the help and suggestions.