nelso419

So I have a problem that my local porsche certified mechanic has given up on. I have a stock 1985.5 944 with 77k miles. Intermittently it will die while driving it or while im sitting idle. No sputtering or any kind of warning. Sometimes I'll wait 40 mins and it'll start, sometimes a few days. There is no tach bounce when I cant start it so I figured it was a bad refrence sensor. So I took it to my porsche guy and he put an oscilloscope on the sensor and confirmed it was bad. He went to replace it and couldn't get it out. Ended up taking the mounting bracket off and both sensors were corroded so he replaced both. It ran good so I took it home. I was in a car wash and it died, no tach bounce. Took it back to them and for a day and night it would not start. They got it into the garage to test for spark and it started. They have been driving it around and can't replicate the problem. They have given up. Any ideas?

nelso419

I forgot to add that inbetween the 2 garage visits my coolant drained out of the car. I took it back to the porsche guys and they found that all the coolant hose clamps were loose (I can thank the previous owner for that) they tightned them up and pressure tested it and it was all set. I don't think that this is related to the above but I thought I would mention it.

divil

Have you looked at the DME relay? Read this and do all the stuff he suggests.

nelso419

I hate that point where you really hope the simple cheap fix isn't the solution cause you've already spent so much on another line of repair.

mytrplseven

When the coolant hoses were found loose, were any of them at the rear of the engine? If so, some of the coolant could have affected the ref sensor connectors at rear of intake manifold. When the ref sensors were replaced, did they include the shim for the speed sensor as well? There is an "8" shaped shim that goes between the speed sensor and the bell housing. If it is not installed with the speed sensor, this will happen:

nelso419

Yeah they were aware of the .8 mm clearance. I don't know where the leak was. Do you mean the coolant could effect the magnet in the sensor or the electronics in the sensor.

mrgreenjeans

Yes, coolant or rainwater or crap thrown up from the bellhousing area gets the sensors dirty.

What concerns me is when the last issue happened. In the car wash. Are you certain you have a sound battery tray as well with no holes, or water ingress into the cabin ?

Water has been known to roll down the vent tray area, down the area around the battery, into the hole or cracks around the frame welding/seams and into the glove box and floor areas. It can find it's way around the dash componentry and attachment brackets as well and corrode the DME.

Any water ( you didn't mention if a Series one or two car ) in the footwell, dash area or leaking onto the top of the reference sensors will cause a malfunction.

I had an early car with only around 7,000 miles exhibit this no start-no tach bounce problem on HUMID DAYS with no evidence of moisture coming into contact with anything. Just humidity. It was the reference sensors. Replaced them and the car runs strong at 80,000 miles further on with never another issue.

Tom M'Guinn

You probably need to replace the harness side connectors for the speed and reference sensors. Intermittent no-start, no-tach-bounce on these cars are very often the result of frayed speed/ref wires where they feed into the connectors. When it happens on the sensor side, it's easiest just to replace the sensors, but since you already did that, you probably have frayed wires under the rubber boots on the harness side of those connectors. Peel back the rubber boots and take a look. I'd say the odds are very good you will see broken insulation on the wires and frayed copper strands, like in the picture below. You can replace just the connectors, but that's kind of a pain, or you can get a patch replacement for the harness from 944online, Lindsey, Speedforce, etc.

http://944online.com/index.php/944-t...r-harness.html

Tom M'Guinn

Missed the water reference in my post above. I had a rust hole in the battery box and it soaked the DME in the rain. Nothing like a dead car on the highway in the driving rain. When I got the DME out a few days later, water was still dripping out of it. It'll never leak again on my watch...

https://rennlist.com/forums/924-931-...options-2.html

But I'd still suspect the connectors, especially if it happens randomly. Most original connectors are living on borrowed time at this point...

divil

+1 actually I got stranded for exactly the same reason (battery tray leaked onto DME). Don't know why I didn't think of that before.

Tom M'Guinn

Well, in your defense, in the original post there's no mention of water and he described it more as a random intermittent issue. That's why I'd still think the connectors are the most likely culprit. If it really is correlated to rain/car washes, then that's a different animal.

nelso419

So annoying that you guys have come up with more ideas than the mechanics who were rebuilding a gt3 when I dropped mine off.

So when im coming out of the car wash, water was dripping out of the seams under the passenger side quarter panel just before the door jam. It drained consistently for like 40 mins after getting out of the wash. So yeah I'm thinking you guys are right on water getting to the DME. Should I just be looking for moisture in that compartment? Or specifically something on the DME? If water was on the DME is it unrepairable? (fyi unrepairable to me means any kind of soldering, I'd rather just buy a new one if it came to that.

Thanks to everyone for the help.

Tom M'Guinn

On mine, you could stick your hand up under the glove box and feel it was all wet under there. I "repaired" mine by taking the cover off and blowing it with compressed air for 5-10 minutes. No solder required and it's been fine ever since. No guarantees they'd all fair so well, especially if it's been getting wet for a long time. That said, is your intermittent issue always related to the car getting wet? If not, or if there is no sign of moisture under the glove box, I'd strongly suspect the connectors.

nelso419

Well before they replaced the sensors themselves the issue was not exclusive to moisture. But they did oscilloscope test the sensors and confirm they were faulty. Atleast that is what they said. But since they replaced the sensors, yes it has only been moisture related. But I haven't had the car long enough to test for a non moisture related failure yet.

nelso419

I won't have the car till Monday.