Head Temperature Sensor Replacement
 

The '80s Carrera head temperature sensor is a well known problem area. The factory shipped it with a single wire unit that relied on the threads of the sensor itself to provide ground. Unfortunatly, this has proven to be unreliable and these things fail routinely.

There is an upgraded part available that has two wires. The second wire provides a ground and proves to be much more reliable.

This is a smart preventive maintence upgrade to avoid trouble before it happens.

Pelican has a tech article describing the replacement. See http://www.pelicanparts.com/techarticles/911_cyl_head_temp_sensor/911_cyl_head_t emp_sensor.htm

But no pictures! So here I have documented my own replacement procedure.

To gain access to the sensor, jack up the driver's side of the car and remove the rear wheel. Here is a picture of the sensor hiding behind the shock absorber, just ahead of the lower valve cover. The white wire is connected to the sensor through a grommet in the sheet metal.
http://www.pelicanparts.com/ultimate...orefrontsm.jpg

I opted to remove the shock to get better access. I have SSIs which made access from the front impossible. If you have regular heat exchangers, the removal of the shock may not be required.

The sensor screws into the head of the no. 3 cylinder and has a wire that passes through the sheet metal and up to the top of the engine. The sensor is accessible from the front of the engine. It is behind a grommet that the temperature sensor wire passes through. Remove the grommet to get access, just pry it out with a screw driver.

Here is a picture of the grommet after removal. That part that appears white is the head, and the round thing is the sensor which screws into the head in the same fashion as a spark plug.
http://www.pelicanparts.com/ultimate...ergrometsm.jpg

The sensor wire then passes back through the sheet metal to route to the top of the engine. Again, passing through a grommet. Here is the grommet at the top of the white wire.
http://www.pelicanparts.com/ultimate...ergrometsm.jpg
Pry out this upper grommet as well. Two other wires share that grommet, just set them aside.

Now move to the topside, inside the engine compartment. The wire routes up near the intake manifold to a connector. In the following picture you see the white wire from the sensor attached to an off-white connector. The connector mounts in a bracket that holds two other connectors. You need to remove the head temperature sensor connector from the bracket.

To remove the head temperature sensor from the bracket, use a pliers to pull a "key" out of the bracket. I don't know what else to call it but a key, look at this picture.
http://www.pelicanparts.com/ultimate...bracket1sm.jpg

Here is a shot of the "key" after removal.
http://www.pelicanparts.com/ultimate...bracket2sm.jpg

Once you have the key out, the off-white connector pulls right out of the bracket. You are ready to install the new sensor and wire.

Move back to the underside of the car.

Cut the old wire off the old sensor. Then use a socket wrench with extension to remove the sensor.

Here is the new sensor and wire. Note that it includes new grommets.
http://www.pelicanparts.com/ultimate...ewsensorsm.jpg

Since the sensor wire is hard to reach behind the manifold, I used the old wire to pull the new one through the sheet metal and back to the topside. I taped the new one to the old as follows:
http://www.pelicanparts.com/ultimate...lthroughsm.jpg

Thread the new sensor into the head. Use a set of long-nose pliers to tighten it down. Apparently there is a special socket for this that accomodates the wire. Get it if you can, else just use long nose pliers. It doesn't have to be very tight.

Note the sensor has some compound on it. Probably an anti-seize and heat conducting grease. Try not to wipe it off.

Return to the top side of the engine and pull the wire up using the old wire that you attached to the new wire.

My car had a ground already available on the connector that the new sensor wire will attach to. This may be true of all Carreras but look to be sure that your car has it. Here is a picture of the connector with two wires:
http://www.pelicanparts.com/ultimate...twowiressm.jpg

Put the sensor wire connector into the bracket, then slide the "key" back in to hold it in place. Now snap the connector back on.

You are done. Fire it up and make sure it is running right.

Now take it out and drive it hard, the way it was meant to driven, with confidence that you won't have any head temperature sensor problems.
----------------
Chuck Moreland '86 Cab - "Sparky", '77 Targa - "Sweet Pea"


[This message has been edited by Clark Griswald (edited 07-28-2001).]

Clark--nifty write-up on replacing the temp. sensor. A suggestion: If you are caught out on the road with the bad sensor and a lot of backfiring and run problems--grab a alligator clipped lead from that multi-meter you ALWAYS carry and clip it to the metal barrel of the sensor and ground the other end somewhere in the engine room. It'll get you home in a pinch. http://www.pelicanparts.com/support/smileys/burn.gif

George 86T

Jorgeman, good tip. If you need to do that roadside emergency, attach the jumper clip up at the connector. It is much easier to reach and doesn't require pulling the wheel going head first under the car to reach the sensor.

Maybe I haven't looked hard enough but I can't seem to find a cylinder head temp sensor that looks like the one in the above pictures on any vendor's web site or catalog. Anyone able to point me in the right direction of where to get it and perhaps even a part number?

Thanks, as usual, for the assistance! :)

Kurt S

Kurt:

http://www.pelicanparts.com/catalog/shopcart/911M/por_911M_FUELMO_main.htm

You up for joining a bunch of other NoVA Pelican heads for a fun run this month?? Let me know.

Maybe :) When?

Kurt

Just did this job my self recently. Not terribly difficult (turned out not to be the source of my problem, but that's another story).
If you need to change one and don't have the special porsche tool, you can make one from a 14mm deep socket and ~15 minutes of work with a die grinder. I think Sears sells a 14mm for ~$4. Just grind ~3/8" slot from top to almost the bottom and it works like a champ. Then add it to your drawer of special tools you'll never need again.

John
`87 Carrera with new:
head temperature sensor
and both flywheel sensors <- they fixed it

Well I took the plunge today and purchased both a new 2-wire CHT sensor and a new DME relay. Changing the sensor was not too difficult, for me the worst part was removing the grommet with the three wires in it, it was just hard to get a good grasp in there to pry it out. Once out however I found that the sheetmetal around it interferred with getting a straight shot in to the sensor with a socket. The angle was wrong and I had to bend the sheetmetal a bit in order to fit the deep socket over the sensor. On my car the sensor turned out however not to be a 14mm but a 13mm.

Regardless, it took about two hours to to it all from jacking it up to rolling it back out the garage. Didn't have a chance to test drive it long enough to really tell if the hesitation problem was gone but it didn't do it for the few miles of my test drive. Time will tell.

Interestingly enough the local shop I purchased the parts from thought that my symptoms just might be cured by the new CHT sensor but gave me a puzzled look when I said that I'd heard a new DME relay might also cure my ills. The shop said a DME relay will often cure a car that doesn't start but that it only sends power to the computer and shouldn't affect the way the car ran.

But, they said try it, you never know.

Anyway, thanks for the tech tips and the replies to my question, as always they were very helpful and informative.

Regards

Kurt S

Head Temperature Sensor Replacement
 

I am in the process of this replacement on my 84 3.2 Carrera as I write, so I can only add more info to this point of the project. It seems that someone previosly replaced the sensor and crossthreaded the threads on the cylinder. I'll have to sort that out tomorrow (8/12/03). The old sensor in my car is the single wire type, and is 13 mm. The new sensor from Porsche carries the 930.606.915.00 designation and is 14 mm.

The metal pan around the back of the motor seems impossible to remove and makes visualizatiion/access very difficult.
I was able to bend a portion out of the way.



(spelling ed. 4/18/06)

rbcsaver:

You are correct. There are 2 different thread sizes. I ordered a recommended part number only to find out that it was the wrong thread size!!!! I ended up buying another that was correct size. There are 13 AND 14mm 2 lead units available.

Maybe someone out there who is a parts guru can give a detail of what size corresponds to what year AND the 2 different part numbers (sizes) for the replacements.

I don't think that the "threads" are different sizes. Putting the side by side the threads appear identical. My guess is that the old single wire units are the 13 mm and the new 2 wire units are bigger to accommodate the ground wire changes. I ordered mine direct from the Porsche dealer.


(spelling/ typo edit 4/18/06)

I can't honestly say that the tread pitch was different between the 2 but the major diameters were. Both of the new ones I ended up with were 2 wire. I wish I kept notes on the part numbers.

Just replaced this sensor. Not bad, couple of hours total with a couple of breaks. It sure did the trick. The car runs 100% better at all speeds and no lurching and missing anymore. I just hope the sensor is tight enough, as I also used the needle nose pliers (vice grips) in lieu of the special socket.

I have a suggestion or two. When removing the grommet to the engine compartment, I took a small allen wrench and slid the short end into one of the wire slits, then turned it across the slit. Then I latched onto the long end with the vice grips, straight into the jaws. After a few tugs and some arm bruises, (it's mighty tight in there) the grommet popped out.

On replacing the grommet, after the wires are all put where they should be, I started the grommet in the hole, then sprayed a bit of white lithium grease on the area. I took a 12" long, 3/8" socket extension, and pushed the rest of the grommet home. I would imagine there are a lot of tools that would work for that.
Hope this helps a bit
Tim

Great post. Thanks for the 'heads up' (no pun intended)

Ouch $61 bucks for that little thing...but most likely worth it so Im gonna do it.

Looks like the price of DME relay has dropped recently here at our host too...

Is this for CIS 911 cars?

This is for the 84+ Motronic cars.

Wayne

Hia!
Thanks to Clark Griswald for a brilliant Thread!
Have done the replacement today in a few hours! The car is running like it should, and hopefully it will pass the Norwegian CO test, witch was why I did the replacement.

Wow, interesting to see my words (mispelled....LOL) and issues of the day resurface years later. Isn't the internet
and all it's resources wonderful?

I have always been leery of using petroleum products on rubber (or unknown similar compositions) products. If the O ring doesn't deteriorate, the grease will always be "there" and possibly inadvertently assist in the O ring being dislodged. I personally prefer a soapy water solution on the rubber O ring in firewalls, wheel wells etc.
regards,
Hope to see y'all at the Hershey Swap this weekend (4/22/06) and 2008

regards
Steve

I must be having a bad day or its the beer I just drank. Read this post and checked CHT plug. Mine looks like the above in the last pic in the thread. How can I confirm it's the two wire?

Jason
88 Cab

See the pic of the greasy finger holding up the plug?...as you view inside...if you find two metallic thingies...it's a two wire system.

If..OTOH...you only see one metallic wire "end" and the other end inside the plug is plastic, or lost-in-action...it's a single wire plug.

- Wil

1st of all - you are drinking beer in salt lake city - what the hell is wrong with you ?

2nd of all - 2 wires poking out means you have the updated 2 hire cht - damn boy, move from florida and you lose all your sense!

Oh man flamed again! I was pretty sure it was the two wire given that plug. Crawled underneath to trace the wire but couldn’t see it with the wheel on. Funny thing, when I went out to check the plug, it was pulled out on one side (i.e skiddy-wampas). So it was a good thing the thread got posted and I checked it in my drunken state.

As far as movin to Salt Lake, I moved as close to the Liquor Store as I could. ;)

Jason
(two-wire CHT 88 911 CAB)

I can;t bust your chops local - so now have to do it long distance!

holy batman! I was like...wha? a thread from Clark Griswald? Gotta be at least a few years old! Good to see the pics are still working :)

Thank You Clark!

This is an Outstanding Post.

I recently replaced my DME relay. Started and ran great for a week now when at cold idle and at stops my baby has rough idles and last night after a 20 minute drive, I started it it hunted (reved up and down) in idle. :-(

PCA tech recommended I check out/replace TCH 1st, but I did the easier and 2nd recommendation DME relay. I guess with this thread it is going to be my weekend work of love.

On that special tool, do you think if I thread the wire through the 5/8" spark plug socket and use a monkey wrench could do the trick or do you thinking the needle nose plyers will torque it enough?

Thanks Again!!!

No = you need a socket to snug it down properly.

Where can I get this because I do not have a grinder as previously suggested to modify a 14MM socket?

BTW, I did a pre-inspection of the CHTS. It is the notrious Single Wire CHTS :(

The plug definitely has two sets of connections and mine is a '85 :-)

Draco,
Perhaps you have a friend with a 4" grinder, pay a shop a few bucks to do it, rent or buy a grinder. They can he had for $40 or so. Cheaper than the labor at a Porsche shop, plus you'll have a tool for future use.
regards, Steve

Hey John,

Could you post a pic of your CHTS Tool Mod???

Found a Pic of the Specialty Tool:

http://www.midwayautosupply.com/imag.../WIL-W1267.jpg

$9.99 at http://www.midwayautosupply.com/p-31476-wilmar-oxygen-sensor-socket-w1267.aspx

Only thing, it comes in 7/8" opening not in metric. Apparently, that is the universal size for most sensors i.e. oxygen etc...

Well Gents and Ladies,

I did the replacement, well almost...:(

Wholy Smokes Batman :eek:. It took me 2.5 hours but I need to advise on a few things:

1. Get or make the 14MM deep socket with slot for the CHTS wire, is a MUST! the needle nose method is just too difficult to manuvere and tighten the sensor to the cylinder head #3. The heat shield will cut into your forearm, not really bad but it will scrap the heck out of it.

Also if you grind the socket make certain the slot is at least 1/2" (or double the width of the base of the new wire where it meets the CHTS) wide and ground all the way to the ratchet insert. It is the only way the wire will not interfere with the tightening of it to the cylinder head.

Sand down the edges as not to cut into the new wire.

Unfortunately, I did not grind enough so I will need to redo the procedure, I just hand tightened the sensor to the head. I did not want to drive my baby without a CHTS, so I temporarily settled with it hand tightened. She runs fine but I will feel much better when it is properly torqued contact (11lbs).

2. Caution, when you install the new rubber plug that holds the CHTS, Speed and Reference Mark Sensor, DO NOT PULL on the wires from underneath the car, it will break the heat worn plastic housing at the 3 plug holder housing, my reference mark sensor fell apart and I had to use rubber insulated (heat resistant) electrical tape to rebuild the housing area so it will sit properly on the "3 sensor plug holder" with the retaining clip. I discovered this while I was finishing up the install. To keep this from happening, I would recommend marking then disconnecting plugs, becareful it may be brittle for us older Pcars. Use a small flat head screw driver to pry the thin wire lock to release the plug from the sensors.

3. Get a Pick and Hook Tool set $7.00 at Autozone. It makes removal of the rubber plug that holds the 3 wired plug much easier. The plug at the #3 cylinder head comes off by hand. Oh yeah the new CHTS rubber plug is scored but not cut all the way through so cut them so the two other wires can slip on. You do not want to do this during your install procedure.

Fishing the CHTS through the hole was quite easiy. I could actually reach in the engine compartment and gently pull it to the 3 plug holder housing.

The new CHTS has anti seize loctite but Pelican sales recommended I use the copper loctite for a better and lasting connection for the CHTS.

4. There two sets of clamps that keep the 3 wires together/neat. One near the left side of the engine just right of the 3 plug holder housing and then one near the CHTS.

5. The original single wire CHTS is definitely a 13MM, I cut the wire at the CHTS but still too long for a standard 13MM socket. I suggest getting a 13MM deep socket $4.00. It was a Biotch to remove, locked tight probably due to age.

Result:

No more hunting after warmed up and driven on the freeway for 1/2 hour.

Maintaining 800 RPMs at idle, no stall or dropping of idle at cold start :)

Smooth Start, Idle and Steady Acceleration.

I will feel much better after I tighten the CHTS after moding the 14MM Deep Socket.

Thanks again CLARK I would have been totaly lost without this thread!!!

hey folks,
thanks for this great thread! I am going to be putting it to use today while I change the CHT on my 3.2l 75s
did the dme relay yesterday and put a SW chip in last week
distrributor cap and rotor as well as plugs and wires done this summer
new alternator in the spring
so little by little everything is being freshened up and the results are very nice
just getting better all the time

ok.
I did mine and the one I replaced was the old style single plug type and it was a thirteen milimeter nut.
my twin plug replacement uses a 14 mm nut but the threads into the cylinder head were identical
so fit was no problem
tightened with a needle nose pliers.
very tight access and the grommets were a bit of a pain in the butt.
I also managed not to tape the old to the new tightly enough and I had to push it through from the bottom instead.... lots of cursing under my breath:D
the key on my car was held in place by two small screws. I didn't notice that in any of the descriptions, but I pulled on it for a few minutes before I noticed... lol
and after everything went back together well.
all in all I think replacing the dme relay was the most effective of the work done.
not sure which i prefer now
O2 sensor plugged in or not... still back to backing it. seems to pick up revs smoother with it unplugged, but with the o2 sensor plugged in it seems to be quicker over 4000 revs.

so,
SW chip
new plugs and wires
new distibutor cap and rotor
new alternator
new relay
and new CHT sensor
big test is starting on a very cold morning... will she or won't she?
anything else I should look into on a near 100,000 mile 3.2

Great it worked out :D

Two Small Screws on the Key? Hmmm your pre '84 must be different. Glad you figured it out.

Yeah, O2 Sensoris my next project, They only last 60K miles so if it has not been changed it may need it.

So far I've Changed:

DME Relay (Starting Issue)
CHTS (Upgraded to Double Wired)
ICV (Idle Hunting and Rough Idle at Stop)
AAV (Dang Buzzing)

O2S ( Pending, 160+ Miles, It's Time )

Well just to refresh this thread after 2 years. Decided to replace the CHT as I am replacing the reference and speed sensors. Thought about it for a few days " What about if I cut the wires and then cannot get the CHT sensor out?". Well that is just about what happened!! Should have trusted my instincts!! Cut the wire and then tried to back out the sensor, well after 26years you can imagine it was not going to be a ' piece of cake". Eventually it started to move but after a few turns it got stiffer, so WD-40'd it tightened it back in a bit and then backed it out, after it was out 5mm, it just kept spinning and would not go in or out!!. A few choice words like 'golly gosh!!' and ;'Oh bother' were heard. I managed to get a broad screwdriver around the back and into the gap between the Head and the CHT and as I started backing out the CHT a bit more I turned the screwdriver in the gap to help force the CHT out. It worked, although the threads on the CHT are stripped I think the threads in the head are OK but just need to be tapped to clean them out:mad:. It could have been worse!! Does anyone know what the thread specs are on this hole for the die size. Thanks all.

Phew! Just finished my own. This thread was invaluable as reference. I managed it without removing shock, just more awkward and takes longer - mine probably took 5 hours!

The new one is 14mm but same thread. I used a ring spanner and cut a gap out of the ring. I found the best way to screw the new one in was to turn the wire with the sensor (do not pull the wire up into the engine bay until the sensor is screwed in). Once it gets started it easy to finish with ring spanner.

The rubber grommets were difficult to remove but went back in easily with washing up liquid as lubricant.

Good job I went into it as I found a ton of other jobs that need doing now! :eek: Heater flapper boxes are shot, and the Dansk pre-silencer I fitted a few years back (and 02 sensor) are rusted to hell - not good quality at all.

Time for beer....http://forums.pelicanparts.com/support/smileys/wat6.gif

THIS IS A VERY GOOD TIP Thanks, Bob


Since the sensor wire is hard to reach behind the manifold, I used the old wire to pull the new one through the sheet metal and back to the topside. I taped the new one to the old as follows:
http://www.pelicanparts.com/ultimate...lthroughsm.jpg

Absolutely, but my advice is to do AFTER you have screwed the new sensor in.

My '88 single wire CHT sensor was rather rusty and original. The plastic at the connector end in the motor compartment just crumbled in my hands. I figured that the removal may be a little stubborn so I soaked the sensor with PBS Blaster overnight and made a slot on a deep 13mm socket. If I cut the wire and had problems I would have a non starting car. Sure enough the soaked CHT sensor would not budge, and the socket spun so before I rounded the rusty CHT off totally I started the car and let it heat up. Put the socket back on on off it came!
Putting the new two wire 14mm sensor in was impossible due the bigger diameter and interference from the engine tin surround. I had to grind some metal away to thread in the new sensor. Also took out the shock and used a string to pull back new connector end into the engine compartment.

CHT Replaced with some pics
 

OK, so just to provide some more pics, I completed the CHT sensor replacement in about 2 hours including making the O2 type sensor 14mm removal socket. I also used the advice to tape the new wire to the old cut wire in order to pull it into the engine bay which worked very well. Using a 4 1/2" angle grinder I was able to cut the necessary slot perfectly (ok, nearly so...).

I first cut the wire off on the old sensor as close as I could and used a bit of PB Blaster first to give it a little more coaxing. Then, using a standard 6 point 14mm socket and a 8 inch wobble extension (seen in enclosed pics)

http://forums.pelicanparts.com/uploa...1348945233.jpg

+ a 6 inch extension it was an easy day to remove the CHT from the side of the car with the tire removed (definitely easier this way). This is the socket without the CHT installed on cylinder #3.

http://forums.pelicanparts.com/uploa...1348945169.jpg

Then I removed the single wire rubber grommet that covers the CHT and the triple wire grommet that leads back into the engine bay. Following that, I had to cut two slots in the new triple rubber grommet (previously mentioned in the thread), and taped the old and new wires together to pull them up. Very easy to do. insert the new plug in the bracket below the heater blower motor (removed the large plastic hose to get better access as well). Finally it was time to push the single and triple rubber grommets into place. The latter, was the most difficult part of the entire adventure, as it's hard rubber and at a weird angle to get to from beneath the car, but easier than from the wheel well side. Job complete. Enjoy the pictures.

http://forums.pelicanparts.com/uploa...1348945278.jpg