Head Temp Sensor Compatibility?

[surflvr911sc]

I bought a new head temp sensor for my 3.6 to replace as preventive maintenance and found that the connector isn’t correct. I searched the archives and it seems that Porsche superceded the part and it now comes w/ the later connector. Pelican couldn’t help me out w/ what I need to adapt it and I don’t want to just rig it up.

Has anyone found the solution for this? TIA

[surflvr911sc]

Two days and three bumps later, I assume that nobody has dealt /w this.

I decided to just run the old one and save the new one for a rainy day. Then, as an after thought, I decided to ohm the old one just to be sure. It’s dead as a doornail, which would explain why the all the old spark plugs looked like it had been running rich.

So now I have no choice, time to change the head temp sensor. I decided to use the old connector and just solder it on to the new sensor. I stopped just short of soldering them when I thought about the polarity.

I am 99% sure that polarity does not matter on the head temp sensor. The measured resistance will be the same regardless of the polarity. As sure as I am about this, I wanted to ask so I will feel comfortable about the 1% of doubt that I have.

[ischmitz]

Ryan,

polarity does not matter. It's a NTC which is a resistor that varies with temperature. NTC's get more conductive with rising temps and PTC get less conductive.

The spec is:

0 deg C.............4.4 -6.8 kOhm
15-30 deg C......1.4 - 3.6 kOhm (this is what you should see)
40 deg C...........1.0 -1.3 kOhm (hm, Highland, may this is what you'll see)
80 deg C............250 - 390 Ohm
100 deg C..........160 - 210 Ohm

Are you sure you measured the right thing. It's wired that it is completely dead. What are you getting? Short or open?

When the sensor is broken (open or short) you'll have cold start problems (no engine speed pick-up) since the engine runs lean. The DME defaults to a warm engine all the time (limb mode). This would not explain a rich condition like you said.

Ingo

Ingo

[surflvr911sc]

Are you home now?? Welcome home if you are, hurry up and get home if you're not.

Thanks for confirming the polarity issue. The old sensor would not give me an ohm reading, or a continuity reading at all so it must be ‘open’.

The DME defaults to a warm engine all the time

I have to disagree about the rich/lean thing. If the sensor is bad and the system sees it as “something’s wrong, let’s pretend the engine is hot” it will run richer to run cooler. If the engine is hot, and you lean it out, it will run hotter.

[ischmitz]

Originally posted by surflvr911sc
I have to disagree about the rich/lean thing. If the sensor is bad and the system sees it as “something’s wrong, let’s pretend the engine is hot” it will run richer to run cooler. If the engine is hot, and you lean it out, it will run hotter.

Ryan, trust me on this one. The head temp sensor is only used for cold start enrichment. The DME does not evaluate CHT to tweak fuel mixture. Once CHT reaches the running temp. threshold the sensor signal won't do a thing per Porsche WSM. In case you have an open or short the DME uses a replacement value stored in the DME that represents operating temperature and throws up fault code 1114.

You might be thinking aircraft engines where you have to use EGT and CHT to adjust the fuel mixture.

Ingo (still from Japan )

[surflvr911sc]

OK Ingo, if you say it twice, I believe you. The one thing I know for sure is that the other one is dead and I don’t need to worry about the polarity of the new one.

I’m surprised that the ECU only uses it for cold start enrichment. I thought I had heard of running problems being attributed to a bad HTS but apparently it could have only been affecting startup.

I wonder if the HTS is often being chased when it really isn’t the problem? Of course, by the number of responses I’ve had I don’t think anyone is replacing their HTC out there.

[Speedster94]

hallo
The new Connectors are the ones from the 993 ,on all Three Plugs :
Head Temp , Knock sensor and Flywheel sensor . At the Dealership you will get the 993 Plug in and you modify the Harness side to fit the new sensor Plug . The rich running looking Spark Plugs are most Times
driving around Town and not free the Engine on the Autobahn from Time to Time . How far are you with the install ?
harald

[surflvr911sc]

Harald, I haven't had much progress since the last update.

Some of my parts at the powder coaters off gassed a bit so he’s reshooting them and they should be done by Wednesday. Once I get them I will be in assembly mode.

My hose guy had to order a couple fittings so they will hopefully be done by Wednesday too.

I welded the oval heat inputs on the B&B heat exchangers, but they are a little off since B&B screwed them to begin w/, so I need to get a little creative to make it all come together.

The oil return tube that goes where the cooler is on the early engines is just about done.

The sheet metal doesn’t look like it requires any modification (other than the cross mount, which is done) so once it’s all together I’ll do a test fit to make sure before they get powder coated.

I’m still hoping that by the end of the month I will just need to pick a date to go for the install. Having to work all or part of the next couple of weekends isn’t helping. I really need to do something about this work stuff that keeps getting in the way but at least I’m home for now.

[ChrisBennet]

Originally posted by surflvr911sc
OK Ingo, if you say it twice, I believe you. The one thing I know for sure is that the other one is dead and I don’t need to worry about the polarity of the new one.

I’m surprised that the ECU only uses it for cold start enrichment. I thought I had heard of running problems being attributed to a bad HTS but apparently it could have only been affecting startup.

I wonder if the HTS is often being chased when it really isn’t the problem? Of course, by the number of responses I’ve had I don’t think anyone is replacing their HTC out there.

The head temp sensor is "seen" by the DME at all times - on the '84-89 Carreras. Apparently, it works differently on the later cars.
-Chris