944 starting gremlins, need some readings verified

Obin Robinson · 05-09-2002, 08:44 AM

ok, last night we checked some readings on the 944:

with an ambient temperature of 55 degrees farenheit, we got:

Auxiliary Air valve: 30 ohms with engine cold.
Engine temp sensor (under air intake boot): 30k ohms.

also, both parts DO have electricity going to them on startup. we still have that odd cold-start gremlin though. car refuses to start when it's too cold outside. this is new since winter as the car would start up no problem when it was cold... so it must be something new since then.

any suggestions? are those resistance readings right for those parts?

thanks!

obin

ch944 · 05-09-2002, 10:18 AM

Obin, I went through the same thing only I had no start below 40* Car turned over fine but just wouldnt fire up. What i did to get it started was boost the battery with a 200 amp booster and she would start. My problem was the reference sensors. Once the car started and warmed up i was good for the day but the next cold morning it was back to the booster or take the truck. The truck won out my first winter. There was never any problem with the way the car ran, which is excellent, just on cold morning starts. I checked everything that first winter and all was fine. I picked up the 2 sensors and bracket on ebay and threw them in last winter after getting fed up. We had days in the single digits and she fired right up within 2 seconds which left me very impressed. I have read that the sensors require a minimum rpm to read the timing. The only logic I can see with boosting was that the bad sensors were not picking up due to a cold cranking condition ( more resistance on the moving parts cold, hence slower cranking rpms on a cold motor?) Try the boosting. I did it for 1-1/2 winters and it didn't hurt anything. Do you have spark while cranking? I had no spark on those cold mornings which led me to the sensors.

ch944

Obin Robinson · 05-10-2002, 08:28 AM

hmmmmm, reference sensors eh? you have a part number on that? i am wondering about the spark also.

one more thing i verified this morning: it cranks SLOWER when cold. makes me wonder about the starter solenoid. sound possible?

thanks!

obin

Bob's944 · Bob's944's Garage

Solenoids don't turn the engine, they move the starter gear into place on the flywheel so the starter motor can turn it. If it's turning slow, it's getting weak power or it's brushes are worn and not transferring the power properly .... you find the weak areas when power is concerned really fast when it's cold out. It should respond to being jumped by anuther battery if it's just a weak battery. If it's still tuning slow with a jump, then that starter sounds like it's time to be rebuilt. I'm guessing that if it turns well with a jump and still doesn't want to start, then the other solutions need to be looked at... like the reference sensor one.

Obin Robinson · 05-10-2002, 11:11 AM

Quote:

Originally posted by Bob's944
I'm guessing that if it turns well with a jump and still doesn't want to start, then the other solutions need to be looked at... like the reference sensor one.

THAT sounds exactly like it. it will still turn with a jump, but not start. i don't want to crank away on the starter for too long either.

any more info on these reference sensors? how much are they?

thanks!

obin

ch944 · 05-10-2002, 05:11 PM

Obin, Porsche changed the bracket at somepoint and put a sleeve on one sensor. Something about a problem of electrical interfeerence between the 2 sensors. In other words the the sensor slips into the sleeve and the sleeve into the bracket. I am pretty sure the sensors are alike reguardless of year. Part #, I'm not sure. But I do remember the dealer refering to the both as reference sensors @ $100 each. I went with an excellent set off ebay. I got the bracket too, $45. The smaller oddball sensor that sits on the lower part of the bracket does nothing. It's not connected to anything and was intended for dealer diognostics. Have you tried boosting with a charger/booster?

ch944