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Worrying break down in the rain today.

B Hanna

B Hanna

New member
Hi all,
I really hope someone out there has some experience that might help me work out what happened today. I took my 964 C2 for a 20 mile spin over to Trimmania, in Finchampstead, to get a quote for some work on my drivers seat (friendly, knowledgeable people...much to like). This trip was planned in the dry but ended up being carried out in around 3 hours of rain which was, at times, Biblical (poor planning and forecasting all round!!). After about 2 1/2 hours, and on a busy dual carriageway at 60mph, the car stopped responding to throttle inputs and I ended up slowing to a stop. The engine was still running but still not responding, then after a few seconds it cut out. I was able to restart the car straight away with the engine now responding to throttle inputs, so I pulled away. A few seconds later the same thing happened again. This happened twice more before I could coax the car onto a garage forecourt. The engine was running rough at this stage and when I pressed the accelerator the odd misfire occurred. I switched everything off and sat there for a couple of minutes. When I tried to start the engine again it fired up straight away and seemed to run normally, responding correctly to the throttle. I was only 3 miles from home, so I tentatively drove on. Everything was normal for the rest of the trip! What happened!!!!
 
Fairly good chance water got in somewhere if it was that wet. Ever happened before? Not easy to diagnose electrical faults! I wouldnt worry about it, you shouldn't really drive in the rain.............[8|]
 
i had something similar after washing the rear grill above the engine. i took out the connectors to the MAF and just checked for water and dried and reseated everything and it was fine. i also suspect it will dry itself if you leave it if it is water. nefore i did that i took distributor apart to check the belt was okay, but that just proved distributor belt was okay!

The other issue could of course be dme, that is what people would suggest had you had this happen in the dry. depending on how old the DME is you might want to take that out and check it. this is what I found after I had a similar instance in the dry https://rennlist.com/forums/964-forum/1196604-do-you-think-it-is-worth-fixing-this-dme.html

You need a magnifying glass or enlarged photo to check the soldering.

I drive mine in the wet all the time btw and not had it from rain, just me washing when car is stationary.

Stephen
 
Thanks for your reply...dry running will be even more of a priority now!!
It has happened before, years ago and also having driven at least half an hour in the rain. I was thinking yesterday that it hasn’t done it for years, but then, I haven’t driven her in the rain for years either!! I have had a very occasional instance of the throttle seeming not to pick up as I would expect, but put it down to poor technique! Whenever I lifted off and reapplied the throttle it picked up just fine. As an explanation for yesterday’s issue, water ingress does sound likely. If it wasn’t, what else could it be? Could this fabled DME relay be at faul?
 
Think the first and easiest place to start is replace the DME relay first and next time it rains take it for a good (local) run and see if you can reproduce the same symptoms.

Check too the MAF cabling (running behind the MAF itself) and cable connector cover underneath the rubber boot - probably need to remove the air filter housing for access. On post '90 models this protective cover, under the rubber boot, was removed as there were cases of it rubbing/pressing against hoses and causing circuit interruptions.

There is a fix by pulling back the rubber boot and removing the connector cover and sliding the rubber boot back in place and a cable tying the cable to the connector. Other thing is to make sure the cable is kept away from the MAF itself - i.e. not in close proximity and ideally held away using one of the metal/plastic brackets. This was one of my first checks when I got my 964. Think I have the TSB somewhere if you need it.

Marcus
 
Thank you so much for those suggestions, I’ll have a go at all of that in the next few days. If you have the TSB I’d love to have a look too, thanks.
 
Found it. However, this PCGB forum platform isn't the best and unable to attach or copy inline the TSB - only allows image urls which is pretty useless. Will PM you with an email address. Don't take the TSB as definitely being your issue though. It's more of a cursory check and improvement if anything. In my case I never experienced the said TSB issue but have the made sure the cabling is well out the way anyway - plus stripped down the MAF completely and cleaned up the electrical/resistor contact slides (more a peace of mind exercise than anything else).
 
I've heard only positive things about SS DME (other than they are bit more expensive than normal DME). if they have stock then I think it would be worth it. the normal ones will all fail eventually though the life is many 10,000s of miles changes so you'll never have to replace a normal one either unless you are doing a lot of miles!

Stephen
 
I have one of the new SS DME Relays, works very well - pre primer I went for

https://www.ftech9.com/new-products/993-ssr-pp

Note "DME " isn't the Relay only technically , DME (Digital Motor Electronics) is normaly refearing to the Motronic ECU under the passenger seat ," DME Relay" is this unit your refering too in the fuse box ;-)

Best place I found to get a rebuilt DME Motronic if needed is Steve Wong https://www.911chips.com/motrepair.htm , I have one of his rebuilt ones as a spare ( just in case I issues ) as he upgrades them to the lastes spec , adds the lates S/W fixes and sorts the weak points out as well and ships very quickly.

As for the issue I would say water /damp ingress somewhere, could be the Distrubutor / hall sensor , coils , HT leads ?
Perhaps run the car in the dark and look at the engine bay for HT breakdown as well ?
 
Hi B Hanna

I had exactly the same symptoms as you describe on your wet drive. Mine was traced to the Lambda Sensor at the Catalytic Converter.

I had mine removed and a stainless bypass fitted. There are tiny vent holes on the sensor and with the Cat heat shield removed water was getting into one or more of the holes which was leading to an incorrect signal to the Motronic ECU. A new Sensor and all was well and has been fine for three or so years since.

I'm not 100% sure that the holes allowed the water ingress or whether there was a hairline crack in the porcelain from when it was refitted. Don't but a cheap generic part (which BYW will work fine as there is nothing special about the Porsche chosen one) as some have larger cooling holes which will allow more water in and subsequently accelerate its failure.

Cheap fix and a certain "Porsche [fell] apart" on line shop had me back on the road with confidence in short order.

Also it's an easy self fix. As you are going to throw the old sensor away, simply cut the electrical cable and spin the sensor off with a spanner. Remove the left hand fan unit if you have reasonably large hands. Pop the connector off, feed the grommet out into the area above the cat. If I need to describe any more, I'd let your specialist or Porsche to do it for you.

Good luck. Burnsy.
 
Thanks for that suggestion, Burnsy, that sounds like an interesting one. The guys at Northway Porsche had thought the DME might not be the culprit because the car didn’t simply cut out. I had wondered about the HT leads as I haven’t replaced those since I’ve had the car since 2003. The car is going in for a paint refresh at Riviera Autobody in the next couple of weeks, so when it gets out from there I’ll have a another look at it all. Great suggestions though, guys, thanks very much for your thought and time.
 
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