Head Temperature Sensor Replacement

[kidrock]

way to go, Skip. I recently replaced my CHT sensor as well, using the same method as you....I picked up a cheap set of Harbor Freight deep metric sockets and used a grinder to create a hollow well as to not damage the wires on the new unit.

I'll tell ya though, that is a tight area to work in. Any pleasure I have now surely came with quite a bit of preliminary pain.

[Skip1]

Kidrock,

I managed to get away with only a scraped forearm (no cuts) fiddling around trying to get the triple grommet in. It is rewarding when you turn the key and it still starts too. In testing, mine won't start without the sensor in place, so was smiling when it worked out.

[PDACPA]

Time for my CHT Sensor (and reviving an old thread while doing my research).

Here are two pictures, one is me holding the wire that come from the left side of the engine compartment and plugs into the bracket that holds the 3 wires (female). The second picture is the base (or male side).

1. Is this the two wire system (believe so as it has two female openings) and is this the part I need to replace?

Pelican Parts - Product Information: 930-606-915-00-M14


2. The male side only appears to have one metal "male part" poking out. Is this correct or is this actually the part that I need to replace and not the CHT Sensor wire? If so, does anyone have that part number or link to Pelican's part catalog? This is the part that looks broken (the plastic is dry and brittle and should there be 2 mental "male parts" poking out)?

Thanks

[JAR0023]

You are holding the harness side of the connector in your hand. It stays. The CHT sensor is the male side that is locked in the bracket. Appears to be one wire. Looks like the connector is broken on the sensor side. If you remove the two reference sensor plugs be careful. They are just as brittle and may break as well. -J

ETA: If you do disconnect the speed and reference sensors, mark one of them (both male and female side) with tape or a paint pen. The connectors are identical and it's possible to re-connect them reversed.

[scarceller]

The side you are holding in your hand (has 2 female pins) is the side that goes to the DME you will not be changing this side.

The male side with 1 pin attached to the bracket is what will be replaced as that male connector has the sensor at the end of this cable. Also, the fact that it has only 1 wire tells us it's the old style sensor. When you get the new sensor it will have 2 pins wired on that male side.

Hope this helps.

[PDACPA]

Thanks @ JAR0023 & scarceller

The light bulb went off! I kept thinking I was replacing the DME side (actually I am thinking the plastic might be a bit brittle on the DME side too and "while in there" replace it.

The part link I listed in the thread, is that the correct part for the male side right? Funny that my 89 had the one wire and not the two as most of the threads seemed to talk about 84-87 having the one wire.

[JAR0023]

Originally Posted by PDACPA

Thanks @ JAR0023 & scarceller

The light bulb went off! I kept thinking I was replacing the DME side (actually I am thinking the plastic might be a bit brittle on the DME side too and "while in there" replace it.

The part link I listed in the thread, is that the correct part for the male side right? Funny that my 89 had the one wire and not the two as most of the threads seemed to talk about 84-87 having the one wire.

I'm far from an expert, but yes, that is the one I would buy. -J

[scarceller]

Yes, the part you listed is what you need.

You may want to spray a tad of PB Blast on that sensor before hand. Not easy to get to it and hard to see what your doing, just take your time with it.

[PDACPA]

Thanks guys.

[Tachin]

I have an '87 and the sensor already has two wires. Is it wise to replace, or am I good to go with the newer grounded two wire version? I have the engine out and am replacing the other two black sensors in the bell housing.

[scarceller]

Originally Posted by Tachin

I have an '87 and the sensor already has two wires. Is it wise to replace, or am I good to go with the newer grounded two wire version? I have the engine out and am replacing the other two black sensors in the bell housing.

If it has 2 wires in the harness on the sensor side you have the new style. You could just simply resistance check it at various temps, like room temp and in the freezer.
At room temp 20C/68F resistance should be in the 2500ohm range

Here's the resistance table:

tempC/Ohms

-30 4700
-20 4500
-10 4300
0 4000
10 3700
20 2500
30 1825
40 1150
50 943
60 735
70 528
80 320
90 253
100 185
110 170
120 155
130 140
140 125
150 110
160 95
170 80
180 65
190 50
200 35
210 20
220 5

If you change the ref and speed sensors on the crank you can purchase the BMW sensors, they are 1/2 the cost of the Porsche ones and function the same. Direct plugin replacement.

BMW Part # is 12-14-1-708-619 or Bosch # 0.261.210.002
Our host has them just search for 12-14-1-708-619 you'll find the Bosch part and another yet cheaper aftermarket part, I have never used the aftermarket one.

[PDACPA]

Upon further inspection (and you might be able to see it in my earlier picture) the part of the CHT sensor wire that goes to the DME has a little part of the plastic (off white) broken off and I am not sure it will stay tight.

Does anyone have a part number?

Also, the metal piece the goes around the connector and I believe locks it in place; does anyone have a part number or name of where i can get it. Mine appears to be missing.

[jtook]

Great thread. I just completed my CHT sensor replacement and just wanted to add one thing that got me stuck. In removing the old sensor, I cut the wire, then attached a 13 mm socket to try to remove the old one wire sensor. It wouldn't budge and I didn't want to apply too much force because I was afraid I would end up with a busted sensor stuck in the cylinder head.

The engine was stone cold. I thought it might come out better if I warmed the engine up, but then I realized I already cut the wire. I tried to start the engine but it wouldn't stay running. (no resistance from the CHT sensor). So I had to rig a variable resistor (0-5000 ohms) I made from Radio Shack, as shown in the picture. I worked great luckily, and after running the engine for 5 mins, I tried again, and the sensor came right out without much force.

So, I'd suggest you warm the engine up before you cut the wire!

[toddadale]

Big time help - thanks for the effort! had the sensor fail - your walk though was very helpful.

[wrxnofx]

I just ran through this task this past weekend. Most of it was not bad, borderline enjoyable. I was enjoying getting to know my car a bit better (even after the busted knuckle when the sensor loosened).

I enjoyed myself right up to when I was unable to thread the new sensor into the hole. It just wouldn't engage in the threads. Finally it did, or so I thought. I began turning it probably 1-2 total turns and decided I must have cross-threaded it based on how difficult it was to turn.

Long story short, I had to make a trip to the hardware store to get a tap and re-tap the threads. Once I did this I was able to successfully engage the sensor.

I can still barely walk after sitting cross-legged on the ground for 3 hours trying to get the stupid sensor to engage, and then the stupid tap to engage.

For anyone's future reference, thread/tap is M10x1.0, which is the finest thread in M10 I believe (not 1.25 or 1.5).

[nene]

Reviving this one:

For the life of me I could not find the culprit of a "choppines" throttle response when my Carrera was cold, oh and also the "hard RPM" drops, which usually got better when warm.

My initial thought based on this boards response was to look for vacuum air leaks, which I did after mocking up a simple smoke machine; no leaks btw. I also purchased a AFR to better dial in the mixture, which I also thought might be the issue, which wasn't, so back to the research.

My next thought was the CHT sensor so I did more research and found this thread, which basically pointed to many of the symptoms the car had. After the replacing the little bastard, the car acted and handled like a dream!!! No more "rich" fuel smells, no more hard morning RPM drops and smoother accelerations.

Thanks to everyone who chipped in with their experiences and findings!

[LUFTKUL]

I agree, this thread was enormously helpful when I replaced all my sensors. Here is my short thread on what I thought was an even easier tool to tighten the new sensor. The old sensor's wire can be cut, but depending on the wall thickness of your socket, you may still need the small HF wrench for removal.
Molykote Substitute and Temp Sensor Tool

[Pigeye]

Bumping this one up with a question - my original 87 was a "1 plug/wire/pin" sensor - looks like the new replacement ones are "2 plug/wire/pin" sensors. The female side of the plug in the engine compartment (left side of bracket) has 2 slots. So, just plug it in and we are good? Or is this yet another thing that needs to be sorted?

thanks for the help - this site is really helpful.

[john walker's workshop]

Plug and play.

[Pigeye]

Originally Posted by john walker's workshop

Plug and play.

Roger that - thanks. Again, this place is great!