Eric Kessel

My 90 C2 has problems that i've associated with the lightened flywheel. When I start it on a cold day, it will stall if I try to drive within the first 30 seconds or so. On a warm day, it's fine...... I finally got around to testing my temp sensor, and after sitting overnight, on a 50F day, the sensor reads 1.4k (at the connector on top of the engine). I drove it on the highway for about 1/2 hour, and checked it again, and it still read 1.4k

Could driving it like this cause serious problems? Or only my stalling, and crappy gas mileage problems? Thanks.
-Eric

(I'll order a replacement on Monday, but i'm worried about what I might have already done driving around for a while like this)

Bill Gregory

The Bentley "Porsche 964 Without Guesswork" book says the cylinder head temp sensors resistance varies between 32 degrees 4.4k-6.8k, 60-85 degrees 1.4k-3.6k, 105 degrees 1.0k-1.3k, 175 degrees 0.250k-0.390k, 265 degrees 0.090k.

horst

Porsche has issued a new, improved cyl head sensor. You can replace it yourself, but it is a bit fiddly. I have forgotten what size socket is needed, but you will need a deep well, cut off the wire, and use the deep well to take the old one out. It may be quite tight- mine was. You will then need to sacrifice the deep well by cutting a slot in the side to allow the installation of the new one with wire attached. ( I tried to get mine out with the sacrifical socket- no dice, it just bent the socket because of the slot). That's why either use another intact socket to remove, or cut socket after removal of original sensor.

Adrian

Dear Eric,
Before replacing the sensor remove it and warm it up manually. Boiling water will give you 100 degrees C. You might want to try and get the temp higher. Your post tends to suggest that it has failed because the value should be somewhat higher when the engine is cold. If the DME detects it as failed it assumes an engine temp of 20 degrees C at all times. This is not good on a cold day. You might want to shove it in the freezer as well. This should cause the resistance to increase.
Ciao,
Adrian
911C4

horst

Adrian, you bring a smile to my face! Are you sure you are not Scottish? Seriously, I like it when people don't just "throw parts" at a car.I have also been accused as being as tight as a clam's a**! Your approach is reasonable; I think mabey a hammer would also provide a diagnosis. On the other side, I have been told by the dealer (who wanted the job on my car) that the new part provides better driveabilty, FWIW. In any case, removing the old one reqired, in my case, cutting the wire, as the socket which I had modified would not remove it. After it is out, that is 1/2 the battle. It only costs $75.00, nowadays the cost of 2 tanks of gas.

Eric Kessel

I'll try and remove it, but i'm confused because after getting the car good and hot, the resistance didn't change (the temp on the dash gauge was around the 8 o'clock line, and the thermostat had opened, and idling, the oil level line was around the middle)

That would indicate the temp should be higher than the resistance was showing, and this could be causing injection issues, right?
-Eric

horst

Suggest you have a dealer Dx w/ a hammer. I like the idea of having the updated part, but as Adrian suggests, if it ain't broke don't fix it- find the root cause of your problem. In my case, it turned out to be TWO things- bad head sensor, AND a bad coil.