Help Diagnose and Fix CHT Problem
 

I've been having a series of issues with idle speed and running rich, and I've run down a list of possible solutions. Waiting for a wide band oxygen sensor to adjust AFM, I decided to try my new multimeter (thanks horse with no name and DRACO) on the CHT. I unplugged the sensor in the engine and LOL. Looks like the housing on the DME side is broken and stuck inside the sensor side plug. The broken plug doesn't seem to fit tightly, which MIGHT explain why I have my idle problems intermittently and only when hot.

It had a lubricant on the contacts (housing is broken, could lubricant cause a short?), and when I measured the OHMS at each contact (I'm not sure which was ground and which was sensor) - one read 364 Kohms which I'm assuming is 364,000 ohms and therefore the ground, and the other read .4-.5 Kohms which is 500 ohms and if that's the sensor, then that's bad

(Engine was off, and cold, sitting overnight)

Should I trust the reading with the lubricant on the contacts? And does this mean CHT is bad?

How to replace the broken plug (it is on the DME side not the sensor side), does this require running the entire wire back to the DME or can I just fix the plug?

Pics Below:

http://forums.pelicanparts.com/uploa...1466602408.jpg

http://forums.pelicanparts.com/uploa...1466602392.jpg

There exists a special grease made for electrical connections that is non-conductive. If you feel your existing grease is causing a short, you may want to clean the old out with brake cleaner, then use the other non-conductive grease, although these connectors don't normally call for any kind of grease.

Yep
 

I probably asked too many questions at once - really I need to solve two things:

• Do my voltmeter readings indicate a dead sensor? I checked threads on replacement and it seems fairly easy.
• How do I replace the wire or the plug, on the DME side, which seems to be broken? Is it possible just to replace the plug section without replacing the entire wire?

Solved one part of the issue - there's a place called Eagleday in Fort Lauderdale that sells the connector, both male and female, called the AMP 2 Pole Jr. Connector. Just ordered one and if it fits I just have to figure out how to connect it back to the old wire. Just leaving this resolution for future reference.

Still curious about the readings on the CHT sensor.

kyngfish -- can't help you on the resistance readings on the CHT, but have you confirmed whether your CHT sensor is an older one wire unit or the newer two wire unit? One wire CHTs were supersceded by the two wire units many years ago and, it's a good idea to replace the one wire with a two wire sensor if you're still using a one wire CHT

It's a one wire unit. and I can replace with the 964 sensor, but looking at the male (DME) side, there's only one active post, so wouldn't I have to create a ground somewhere to make that work? Also, it looks like that connector is broken and I have no idea how to remove the male (DME) side from that metal harness it's in... If anyone has some creative ideas I'm all ears.

Worst case I guess I can cut the wire and splice in a new connector and let it hang loose?

This is the one you need: 930-606-915-00-M14

It's grounded by the engine.

To remove the male side, remove heater blower motor plastic hose, pull the metal retainer on the harness mount then the male side will slip out.

Use electronic parts cleaner as Brake Cleaner is to harsh for plastics and rubbers.

Draco, once again saving my life. I swear I've learned more about these cars in the last week than in the last 2 years.

I've ordered the male connector, if it's that easy then I'll do both that and the sensor this weekend.

Another option is the junkyard. Almost all older BMW from the 90's and also Porsche 924 and 944 have the same style connectors on their wiring harnesses. So you could salvage a portion and splice it into the existing DME harness.

And your measurements are not conclusive. The 500 Ohm was probably the one-wire to the sensor that is somewhat grounded by the sensor screwed into the head. The other measurement is open and meaningless. What's happening is that corrosion in the thread of the sensor to the head makes the grounding marginal and when the heads warm up it changes. So while the reading of 500 Ohm is correct this can change any second while the engine is running. So as others said change the sensor to the newer style 2-wire that doesn't rely on GND through its housing.

Cheers,
Ingo

Thanks Ingo, I actually went back last night and tested it differently. This time the reading made more sense. I was getting 1094 Ohms in a cold state, with an ambient temperature of 88. Should be much higher, I think it's a bad sensor.

Also I found the connectors at a place called EAGLE DAY in Fort Lauderdale. Can't confirm its the exact one, but it looks right, and I called them and he said they were all over Bimmer and Porsche back in the day.

I should have the connector tomorrow and I'll go pick up the sensor DRACO recommended locally on Saturday morning and do the job.

Wish me luck :/