Engine died, then tach stopped reading with a low rough idle

[cro-cro]

Right before this I was driving and it randomly stalled, so while rolling I cranked it again and the engine turned but wouldn't fire. It acted like I ran out of gas, so I ran and put some more in. When I opened the gas cap a large suction of air went in(that noise happened before but not this big, I wondered if it was the reason the car shut off) cranked it once and it was going again, then when I got on my road when decelerating the engine sounded like it was dying again, the tach was dropping and then I hit the gas and it picked back up. The finally the tach stopped reading and the idle was low and kinda sounded like an old car cold start.

I actually was using my gopro when the car died, Ill shorten it and upload it.

Porsche 944 85.5 n/a rough idle and tach not reading - YouTube

[cro-cro]

This is a better view of what was going on.

Porsche 944 85.5 n/a tach freaking out - YouTube

[jwade944]

Check voltage at battery and alternator.

[cro-cro]

Check voltage at battery and alternator.

Alright, will do, thanks, I saw on other forums it could be the dme or ignition relay? Idk, it was raining heavily yesterday.

[mytrplseven]

Was the car sitting out in the rain? If so, check the carpet it the passenger footwell. If it's wet you've got a leak (high probability of a rusted battery box) and it's soaking the DME. Since your's is a later (85.5) car, the DME is under the pax footwell carpet near the firewall (under the wood panel). If it's wet down there, take the dme out and drain the water out of it (small drain holes) and let it set in the sun for a day and then try it again. Hopefully nothing got fried.

[porschetub]

Crank sensors?

[Tervuren]

Originally Posted by cro-cro

Alright, will do, thanks, I saw on other forums it could be the dme or ignition relay? Idk, it was raining heavily yesterday.

These would not have a effect on the tach like you are seeing.

Either you have unstable voltage to the electronics, or there is water messing with the DME or Speed sensor.

The engine sees the reference sensor get a reading, and uses the info from the speed sensor to know when to fire the injectors and ignition. So if the speed sensor isn't reading correctly, it will only fire correctly on the first cylinder driven by the reference sensor, and get progressively off on the others each revolution because its timing will be off thinking the other cylinders need fuel/spark at different times then they actually do.

A voltage check would be the easiest first step. Also, check for water where the DME sits. You might want to unplug your speed and reference sensors and hit the contacts with contact cleaner as well.

[cro-cro]

I just got back from my vacation and took my car to advanced auto to get a reading, there was about a gallon of water in the battery box. The readings said the battery was around 750 and the alt said nothing. I came home and vacuumed out all the water. When I was driving it would fire but some times sputter like Tevuren was saying. Is the alt really dead, or does it need to dry out and whatnot? I definitely need to drill some holes in the box. how long does it take to change an alt?

[cro-cro]

Also, Im in Mooresville, planning on goin back to Wilmington today, I wasnt sure if the car would make it 4 hours. Frustrated!

[cro-cro]

I put a voltage checker on it and it read 13.5 when the car was running. Befuddled, but I'm gonna get a spare battery and hit the road to Wilmy.

[cro-cro]

I made it from Mooresville to Wilmington, the batt gauge was going down the longer I was driving, I actually got a spare battery to bring with me for to make sure I could go the whole way, but didn't have to use it. The terminals still read above 13.5 while driving, but I'm gonna get the alt bench marked to see what is going on.

[kfanazini]

While driving in the rain yesterday I lost my tach. No other problems just a dead tach. Shut the car down and restarted and it worked, but I am worried.