Electrical Frustration: Mechanic cannot duplicate
 

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.

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

+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

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.

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

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

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.

Spark Plugs?

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.

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.

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

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.

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." ... ;)

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...

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.

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.

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

Key word is intermitant. Fixed 1000's of electrical equipement and nothing infuriats me more than the problem that won't show itself till your doing somthing else. Then try to imulate it!

+1 Intermitent problem(s) can't be found without process of elimination which unfortunately requires throwing parts at the problem.Some of these parts are what I consider maintenance items as they do fail due to age.

I'm with anyone who suggested:
1) DME (Fuel Pump) Relay and related contacts
2) Ignition Switch

ditto.... check you reference sensors mine does the same thing once in a blue moon,either the connections are corroded or they are failing.DME would be you other choice,check connections.let me know what happens.

UPDATE: It finally failed for the mechanics! They are thinking probably a reference sensor or a DME. Something that regulates power to the coil. They didn't get the chance to test it when it failed because it started up by the time they got the equipment out to it. At least they know I'm not crazy. I'm pretty sure it's not the ignition switch because I can beat on it and wiggle it and it doesn't start. It always comes down to waiting. We'll see if they can't get it to fail one more time, long enough to test it. I trust these guys. There were 2 early 911's with the engines pulled out when I dropped mine off, so I no Porsche owners trust them with their cars and they have experience there. I'll keep you guys posted.

The ignition switch provides power to the coil. The DME grounds the coil to fire it.

Your ignition switch "test" is bogus.

It would be interesting to see if the car is loosing the injector pulse as well as spark.
Since you made no mention to black smoke when the car does re-fire I would suspect it is.

Another vote for the DME (Fuel Pump) Relay. Relays usually go bad slowly because of rusty / weak contacts. It's easy enough to just put in a new relay. (If it isn't the relay, you can keep one as a spare. They do go bad.)

When it fails.... tap the dme.

More than likely bad soldering point on the ignition driver....

Motor Meister has probably 10 times as many cars with their engines pulled, people trust them -- doesn't make them trustworthy... FYI.

Glad they were finally able to replicate the problem. Now they can get to repairing it. Way I tested for bad speed/ref sensors was with an oscilliscope... Let the car run and wait for it to show irregular spikes on the graph.

Not a lot of people know how to correctly operate an ossiliscope. If all else fails use, there is always driving arouns with a volt meter hooked up. Black lead to ground, place the meter on your console and hook the red lead to whatever point you want to monitor. DC volt scale and watch. Positive side of coil or negative. Positive will maintain 7-12 volts constant. Ground will be 0-.4 volts and float to 7-12 if the conection is off. Same for any other point monitord.

I know a local Porsche shop with a very respected owner/mechanic. I'm in there one day waiting for Oly and watching a mechanic wack on the side of a control arm to pop out the ball joint (BMW) and low and behold, he hits the fender square. Wipes off the smudge and keeps working. You think he told his boss or the owner?

LOL paul, remind me never to go there!

Which shop is this... come..on do tell... .

Hopefully you figure out what it is, as there are the several possibilities that have been stated here. My car behaved like this for about 2 weeks while my reference sensor was on its way out, but luckily for me it decided to completely die one day... What color/yr/model 944 do you have? I will have to keep any eye out for you on the roadSmileWavy

It's a 1987 Silver 944 N/A. Do you live in the city or the suburbs? I go to Hamline, so I'm in Midway, St. Paul.

If the ignition switch was bad, would the car die while idling and fail to start, or would the problem only occur while trying to start the car?

Find and read then perform the five minute test.

SoCal- Found it, read it, and now I'm gonna take my car back from the mechanic this weekend and see if I can't track this down. Thanks.

I'm assuming this is the test to which you refer:

Well the shop was I believe Furtmier motors? here in Bridgport. Part of Kitchener. Not the freindlyist guy either. Stopped by one day after buying a lot of parts, to ask a general question with the spun #2 bearing in my hand. Looked at me like, what do you want, pay me for the work. Last time I go in there.

Part of it. Once these findings are made there are further check points. Most of the time it's the DME relay and/or the sensors.

Got my car back from the mechanic today. They found a burned out pin on the DME; one that would interfere with spark to the coil. I have a new pin soldered in and it didn't cost an arm and a leg. I'll hope this solves the problem, but IF it fails on me again, I'll run the test and we'll go from there. Here's to hoping...