Electrical Frustration: Mechanic cannot duplicate

[Pistol Pete]

Regarding my 1987 944 NA

So I've had this ongoing electrical problem pretty much since I bought the car. I've posted a few times here and on Rennlist as things develop. I post now because the problem has changed once again.
To summarize the story so far, the car has an intermittent electrical failure that prevents it from starting. It always starts after it has sat overnight or for several hours. 95% of the time, it starts within 5 minutes of being shut off. After I drive it, it can sit for 30 or 45 minutes, sometimes more, and it will not start. I've discovered that the no-start is due to a lack of spark. The starter turns over, but the engine does not fire.
Things I have replaced:
Ignition wires
distributor cap
distributor rotor
removed old aftermarket alarm system

I have a new ignition switch, but have not yet been able to get it in.

So up until last week, the car had never had a single problem while it was running. The only problem was starting the car within the particular problem interval. Last week, I was in the drive through line at the bank on an 80 degree day here in Minnesota. The car died in line while it was idling and would not start again. I popped the hood, put a spark plug on the end of the coil wire, and sure enough, no spark. This is the first and only time this has happened while the car was running, but the symptoms were identical to any of the other no-starts.

I dropped it off with a reputable import mechanic later that night. They have run the car, driven the car, and started it at various intervals since shutting it off. Of course, it starts perfectly every time. I have had problems nearly every time I have driven it for several months now. I am getting extremely frustrated. Does anyone have ANY suggestions? I'm about to give up on this thing.

[Blondie]

Reference sensors? The gap between the sensors and the flywheel could have fluctuated with the hotter weather (aluminium block) and distorted the signal.

[many944s]

+1 on reference sensor. First check the connector, as often they corrode, or even brake. Try stressing the connector while the engine is running, my bet is, it will die out. I have seen a couple of cars where the old connectors were removed and new ones installed, it beats dropping the $$ on a whole new sensor!

Hope it helps!
-Nick

[Pistol Pete]

I'm not sure if it's heat related. There have been times where it has run for 5 minutes early in the morning, sat for 5 hours, and still not started.

[toolboy62]

cracked solder joints within the ECU can also cause this behavior. fortunately (since I did not have the time to do it myself) my local shop was able to resolder it for me rather than sell me a whole new ECU (if they can even get them)

nate

[Blondie]

Try the wiggling of the reference sensor wires..clean out the connections and report back here at 0800 hours.

[Pistol Pete]

The car is actually at the mechanic's still. They've had it for a week now and have been trying to get it to do its thing the whole time. As my luck with this car would have it, it starts perfectly every time. He even made a point of telling me how well it runs. I'm gonna leave it there for another week.
The problem with this whole thing is that I can't figure out what the problem is because it happens intermittently. I thought it might be the faulty alarm system, so I had that uninstalled last month. The car was fine for a couple of days and I thought I had cured it. Of course, it started to act up again shortly thereafter.

[thekidd]

Spark Plugs?

[onZedge]

Everybody forget about the lowly DME/Fuel Pump relay? Could be a bad relay or a loose "pin" in the DME/Fuel Pump relay socket itself.

[SoCal Driver]

Better find and print the five minute test plan and give it to the mechanics.

[Pistol Pete]

Originally posted by SoCal Driver
Better find and print the five minute test plan and give it to the mechanics.

5-minute test plan? Is this something I should know about? The problem is, it always fails to start when I'm out using it, not in my garage.

[onZedge]

HMM...something to laminate and keep in the glove box I suppose.

[SoCal Driver]

Originally posted by Pistol Pete
5-minute test plan? Is this something I should know about? The problem is, it always fails to start when I'm out using it, not in my garage.

Do a search on my user name and "test plan". Basically a simplification of the factory test plan. Has to be done in a certain order to eliminate possible causes.

[Brando]

Keep in mind, sometimes "We couldn't replicate the problem." translates into "This is more work than we're willing to take on." or even sometimes "We can't make any money on this job." ...

[SoCal Driver]

One of the reasons we learn to fix our own cars.

[Brando]

Originally posted by SoCal Driver
One of the reasons we learn to fix our own cars.

And sometimes... If it's a job on a car I reeeeeeaally don't want to work on, I'll say "I've never seen one of these before... You sure it's a Porsche? Really? Hum, I don't know anything about those..."

Not really though...

If it's an intermittant electrical problem, start with the ignition switch. They're not too difficult to replace and do solve a lot of these issues. The contacts inside don't make contact at a certain angle, you wiggle the key and everything's fine.

Check your DME, make sure it's plugged into the harness connector fully.

Only other option I can think of would be failing speed and or reference sensors. My dad's 964 exhibited the same symptoms until we replaced it...

[Pistol Pete]

I used to think ignition switch was the answer, but I wiggle and pound away and it still doesn't start. And the one time it died while it was idling dispelled any more thoughts I had on the ignition switch. I have receipts for the speed and reference sensors...PO replaced them.

[SoCal Driver]

Unless you are willing to put a bit of time into testing and eliminating potential problems you are just throwing parts at it.

[Pistol Pete]

Originally posted by SoCal Driver
Unless you are willing to put a bit of time into testing and eliminating potential problems you are just throwing parts at it.

Yeah, that's why I brought it to the mechanic. The problem is, it only malfunctions when I've been driving it. I'm usually out and don't have it in the garage. Also, I know relatively little about the electrical systems in these cars.

[SoCal Driver]

If you can read a digital volt meter you can test 90% toward finding and fixing the problem.