Porsche Enthusiasts Club Forum

Is there a common failure on the electrical side that causes...

Was driving along this lunch (engine was warm) all of a sudden my engine started misfiring and started jerking (intermittent electrics?) and then cut out, initially for the first turn over it wouldn't start then started again, on the way home from work it was fine to.

My wife did try saying this happened to her last week but when I went out in it last week all was fine!

I've checked most electrical plugs for tightness/cleanliness are there any common component failings that cause this type of error??

Mine S2 did this cutting out thing too. It was a dirty plug on the side of the MAF. I found the problem by accident. Then I took the plug off, cleaned it, put it back on securely - never had a problem since.

DME relay would be my first thought.

Likely candidates: DME relay, FPR and the plug at the back of the cam cover.

I'd go for DME relay as well, and only about £20-25, so cheap fix hopefully, you can check the date on the relay, bet its the original one

Intermittent faults like this are always a pain to track down, even with a workshop with a stack of tools and diagnostic kit. Especially if it will not play up when you are waiting and hoping for it play up, it is much easier to find fault with a car that just will not run at all.

Your 944 can log diagnostic fault codes, but 9 times out of 10 the cause of a problem will not be something that the ECU will be aware of being an issue and the diagnostic side of the ECU is quite basic.

A crank sensor could be one option, their resistance tends to drift out of spec as they age. Typically they have around 900 ohms between 2 of the 3 pins, I would not be to concerned if the resistance was anywhere from 600ohms to 1200ohms, often it is not the sensor which has gone to the wall, but the wire from the sensor plug to the sensor, which is a moulded part of the sensor, the wiring inside the cable tends to develop breaks due to vibration over tens of thousands of miles or several years of heat cycling.

Quite often though, a crank sensor will just completely die and cut out permanently.

Wiring to the airflow meter sometimes can become intermittent and cause stalling from time to time. But often if you wiggle the wiring while the car is running you can cause it to stumble if this is the issue.

Quite often we have found fuel pumps to be a cause of intermittent cutting out, which will cause misfires and splutters as they die.

Sorry I can not be of more help, this kind of issue can often require either living with the fault until the fault becomes more permanent, at which point diagnosis is much easier (not what you want to hear) or handing over to a specialist who can test each sensor one by one, and wiggle test everything while monitoring sensor values, as well as reading the fault codes... But even then you may be left with a list of sensors and components which are due to age operating at their edge of viability, which would be recommended are changed, with only a guarantee that they have a clean bill of health and it may still not be the problem (but will more often than not be the cause)

Hi there,
I'm a newbie to these boards but I'm really hoping that you guys can help me with an intermittent problem I'm having with my recently purchsed 1990 944 Turbo.

**** nutnboltcombat - please tell me you found the fault, this could've been my post **********

Here's my story:

I'll start at the beginning - about 3 weeks ago, I purchased a lovely 1990 944 Turbo with an unprecidented history file - this car has really been looked after throughout it's 25 year and 135,000 mile life. In the following fortnight the car performed faultlessly, including the 250 mile journey back from purchasing the car.

Last week after a brief visit to my parents (about 5 miles away), I started home. I'd gotten about a quarter mile down the road when I felt the car falter and shortly after the engine stalled. I managed to restart it but it was running EXTREMELY rough and wouldn't idle. The only way to keep the engine running was to keep on blipping the throttle - it was obvious that the engine was "missing" badly and there was a strong smell of petrol from the exhaust. After nursing it back to my parents I left it parked-up overnight.
I returned the following day to assess the sitaution and to my surprise, when I tried to start the car, it started and ran perfectly. I drove it around the block a number of times and decided that perhaps what had happened was somehow a "glitch". However, just to be on the safe side, I changed the DME relay, plugs, leads, distributer cap and rotor arm - I also had a new throttle position sensor fitted. (I've also bought an engine temperature switch just in case it was faulty and telling the ECU to over richen the fuel BUT I haven't fitted this as yet).

Everything was fine until yesterday. After returning home after a long Sunday blast, I pulled-up outside my house and hit the door unlock button in order to let the wife out of the car before parking-up. The instant I hit the door unlock, the engine faultered and died. Again, upon restarting the engine it wouldn't idle, ran rough and would only keep running if I kept blipping the throttle.
This morning I went to start the car expecting difficulty but you've guessed it - it started, idled and ran flawlessly! I even tried to re-create the issue by pressing the door release button but it was perfect and had no effect on the engine.
It seems that whatever is causing the issue is resolved after the engine has gone cold!
Don't make the mistake of thinking I know what I'm talking about, I'm the first to admit I'm not partucularly mechanically minded so I really need your help as I don't know where to go from here.
Do I need a mechanic or an auto-electrician?
Could it be the temperature sensor switch (I'm going to fit this when I get a little time).
Could it be the Mass Air Flow sensor?
Coil?
Bad earth?
I also have a "Scorpion Alarm" fitted - not sure how it could be this but you do hear of problems with 3rd party alarm fitments.

Thanks in anticipation guys.