[968Bud]

My 1993 Porsche 968 will intermittently shut down while in motion. No check engine light. Just a fast sudden no warning shut down. If apply throttle a while still in motion, there is no difference. If I turn the ignition key on and off a few times while in motion it will not respond. When I coast the car to the side of the road, I will attempt to restart it. Sometimes it will fire up immediately. Sometimes (with continued on and off cranking) I will have to wait a full 120 seconds before it will start. When it does start, it runs like it had no problem and no problem occurred.



I have replaced relays but the problem still re-occurs. No Codes are reported at all when running the diagnostic software. Sometimes I will drive 150 to 200 miles between these occurrences…. I have worked on 944’s and 968’s for 25 years. I’m stymied! What can I do?



968Bud

Partial Post: Please Login or Register to read the full post.

[tamathumper]

Which relays did you replace, specifically?



Also, when you try to restart it, does the starter always crank vigorously or is everything dead?

Partial Post: Please Login or Register to read the full post.

[ds968]

This is the most unique ( and bizarre ) symptom I have evr heard of, or read about to date. Curious to learn what the possible causes may be.

Partial Post: Please Login or Register to read the full post.

[968Bud]

Thanks for the quick reply! I replaced all of the relays. I had a complete spare set on hand. The stater cranks with full speed. I have a spare crank positioning sensor. I'm going to swap that out now! I will report my findings.

Partial Post: Please Login or Register to read the full post.

[Chris Vais]

If it isn't electrical the only other thing that I can think of would be a problem in the fuel delivery, but that doesn't explain your ability to restart the car once you've come to a stop. Is it possible that you are experiencing an intermittent loss of fuel pressure? I think I'd go through the fuel system from tank to injectors looking for a partial blockage.

Partial Post: Please Login or Register to read the full post.

[Cloud9...68]

It sounds like the shut-off is too sudden for it to be fuel related, if I understand the symptoms correctly. I would think it would spit and sputter for a few seconds if the fuel delivery were the issue.



Have you checked the coil, and the coil wire? I don't know if there's a reliable way to test the coil, but I would think any problems with it and its wire could be temperature related, thus the failure at speed, which means the car has had time to warm up. Is the problem more likely to occur on a hot day after you've driven the car awhile?

Partial Post: Please Login or Register to read the full post.

[Gotter]

Our old 2000 Subaru Outback began to do this as well.... very dangerous at 75+ MPH. They never figured it out. Many batteries chewed through in matter of weeks, Alternator replaced, was a nightmare. Good Luck!!!

Partial Post: Please Login or Register to read the full post.

[bombfactory]

Could be worn or deteriorating battery/alternator/starter cables grounding out. There is another thread currently going on about this issue.

Partial Post: Please Login or Register to read the full post.

[RS Barn]

You need to start with basics. When car shuts off-have a spare spark plug with you and install in #1 spark plug wire. have someone crank over engine to see if you have spark.

A simple way to find out if it is fuel related is to jumper the dme to turn on fuel pump and then replace dme and try to start. If it was fuel related and you filled fuel rail, car will try to start.

If fuel pump quits working while driving, car will shut of in a second or two.

Partial Post: Please Login or Register to read the full post.

[Chris Vais]

The fuel pump in this car is electric, so if you had a bad ground or bad power connection to the fuel pump it would shut off. These are old cars as you well know and the chief source of electrical gremlins on mine has been as the result of poor ground connections/power connections.

Partial Post: Please Login or Register to read the full post.

[968Bud]

While swapping out the crank positioning sensor, I had found a dry rotteted and broke rubber vacuum hose connector. It resides under the intake manifold between runner 3 & 4. I replaced it. I have put 250 miles on the car so far and no abrupt cut outs yet. I know that the fuel regulator has a vac line on it. Do you think that some sort of vacuum drop at 3,000 RPM is drastic enough to trigger that diaphram that is in the regulator? Think about that? I will continue to drive and report to you guys. I thank you for all of your input!

Partial Post: Please Login or Register to read the full post.

[968Bud]

Spoke too soon. It shut down again on the way to work yesterday. However, I had such a good roll going, that i was able to key it back on as it dropped from 70 mph down to 40 mph. It leads me to believe that there is something relevant to "time" before something is re-setting.



This weekend I will taget all of the suggestions of Chris, Cloud 9....68, JC, Bombfactory and RS Barn. Thanks for all of your help on this guys. I will report to you my findings. I'm sure we will get some closer out of this thread!

Bud Hoffmann

Partial Post: Please Login or Register to read the full post.

[flash]

that is exactly what my car was doing when my DME relay was failing but had not yet died.

Partial Post: Please Login or Register to read the full post.

[tamathumper]

As an additional data point, my buddy's Boxster died once or twice and he had to replace the ignition switch, but I don't know if that has any similarity to the 968. Just thought I'd throw that out there for you.

Partial Post: Please Login or Register to read the full post.

[DaveN]

I would build the little DME relay jumper wires from Clarks Garage and carry those with you in case it is just a matter of a funky relay. I keep them in the rear cubby permanently. At least if your car dies permanently you can force the pump on and see if you can drive home.

Partial Post: Please Login or Register to read the full post.

[jimmywhisker]

I seem to have most of the problems ever posted here!!



I just experienced a similar problem, it turns out that one of my sensors was malfunctioning, creating a severe electrical short and shutting the computer shut down with obvious consequenses. Not sure of the exact technical details as how this happened, however, a new variocam sensor fixed the problem.



My car would just stop for no reason but would start again and drive perfectly for awhile. I also experiened little micro stalls at times when crusing. Perhaps you could have a look in this direction if all else fails.



I also had a faulty o2 sensor for which replacement has improved the intermittant gas smell in the cabin.



Now the annoying knock/rattle that eludes me.



Cheers,

Peter

Partial Post: Please Login or Register to read the full post.

[tamathumper]

[quote name='jimmywhisker' timestamp='1344044454' post='130493']

I also had a faulty o2 sensor for which replacement has improved the intermittant gas smell in the cabin.

[/quote]

May I ask when would you get the intermittent gas smell? After the car was sitting overnight, or while driving? Was it a raw gasoline smell, or a smell of exhaust fumes?

Partial Post: Please Login or Register to read the full post.

[jimmywhisker]

Hi TT,



I am not sure that the problem will be rectfified as i have only had the car for 10 days. However, the gas smell was most noticable when the car sat overnight after a short run, when driving with the sunroof out and the windows up. I would also occassionally notice it when i walked past the rear after a short drive. The smell was more of a combination but i would say leans towards a raw gas smell.



In looking into this, i had checked for smell when on the hoist, taken the rear mats and reseasled the cover around the filler neck, tried all sorts of combinations of how full to fill fuel tank, different types of fuel. The smell has never ben consistent so i cannot guarantee that the o2 sensor was the problem however, i did read instances of others ( not 968's) having similar symptoms/solution.



Hope this helps.



For me, Nothing beats the difficulty and expense of the crown wheel and pinion bearing noise for cost so far. If i could resolve that annoying knock/rattle in the right front i would be a very happy man. Worked through most of Flash's tips but no luck so far.



Cheers,



Peter

Partial Post: Please Login or Register to read the full post.

[968Bud]

I inspected the fuel pump ground they looked very clean. I went ahead and dremil polished the brass land and cleaned the terminal lugs at the fuel pump ground. The I put another 200 miles on the car, and it did the same thing yesterday morning at 55 mph it shut down again. It appears again that some sort of time interval determines a "reseting condition" I had the ingnition switch off while coasting down to about 35mph and the car came back alive while I was still in motion. "Should I buy a good used DME and swap it out out" Problem still not solved.

Also to DaveN The DME relay was replaced with new!

Partial Post: Please Login or Register to read the full post.

[DaveN]

I had the same problem on my 944 and it turned out to be a cold solder joint in the DME. You don't even want to go there! I Took me forever to find that. I think, for the most part, the quality of construction has been excellent on the 968 electronics.

Partial Post: Please Login or Register to read the full post.