speed and reference sensor
 

Hi everybody according to bentley manual to test the terminal resistance 1 and 2 is 960+- 96 ohm which I within spec, but terminal 1and 3 and 2 and 3 should be > 100000 ohm I cannot get any reading at all, is that means I have to replace both sensor? if I have to replace is that anyway without drop the engine, thanks for you input.

I can't attest to the measurement, but it is possible to do both sensors without dropping the engine. It's more of a pain in the butt, however it can be done. The short version

-Jack up the car
-remove driver side rear wheel
-crawl under and look on the driver side to locate the sensors and bracket
-there are (2) 5mm allen screws holding in both sensors
-if you can remove them without removing the bracket that would be best
(I wasn't so lucky and had to remove the bracket as my reference sensor was stuck in the socket)
-if you have to remove the bracket put the old sensor back in and tape a 8 mm washer on the end of it. Then bolt the bracket back in. The washer will make sure that the new sensor is at the correct spacing.
-Pull the old sensor back out and put the new ones back in.

Also if you do a search there is a thread with pictures showing you how to do it.

Good luck

There is a grommet with the CHT sensor wire in it, as well as the reference sensor wires. It can be a bit of a pain to remove and put back in. Also a clamp in the engine compartment is inconvenient to get to. Still doable, if I can do it in 3 or 4 hours, most folks should be able to do it in 2.

Search for Schnellman's post on reference sensors - he lists a BMW part number from our host that is the same part for $50 less. I have one, and it works.

thanks I still want to know whether it works or not before this pita job, cause the car miss sometime not all the time I do check dme , coil , distributor, rotor ground and relay also order new ground stripe ,even head temp sensor ok , etc etc, only this ref and speed sensors is the last point to look after, anyway thanks alot.

The fact you do not get a reading is GOOD. The sensors have a braided shield on pin 3 and two signal wires on pin 1 and 2 to the internal electric coil. The resistance between the two signal wires is 960 Ohms and there shouldn't be any significant leakage between either signal wire and the braided shielding on pin 3. Based on your measurements the sensors and the cable are perfect. Keep in mind this reading could change once the cables get wet.

Ingo

thanks Ingo, I will leave it and keep driving .

Bad news after test drive, found engine miss in 2 to 3k rpm , after restart normal again, sometimes drive wholeday nothing happen sometime it happen on and off ,really upset, already change plugs, dme relay fuel pump, filter, even a new coil, clean and balance injectors,any input is welcome.

With the car securely on jackstands, run the engine and jiggle/wiggle the wires where the sensors read the flywheel at the transmission bellhousing. If the missing occurs when you disturb the sensor wires, you need to replace them.

I have a cold start problem (doesn't want to pull away) and miss/lumpy idle when warm, otherwise drives great when warm.

I have checked the resistance of both sensors and the speed sensor is slightly out of spec - reading 1095, is that enough to cause problems? I did notice the plastic sheilding is broken near the sensor (when I changed CHT).

Cheers

Hi Rich,

You're just a smidge off, and while I don't know if that be enough to contribute, it could indicate that they are leaking/varying with movement and moisture (not good).

I do think you should change them because as the age, the value will get worse.
If you see crumbling (and you handled them), the problem will accelerate. The insulation on mine just fell off in many pieces as I removed them.
(BMW parts are compatible {Bosch} and less costly)

Also, if you wanted, you could measure the lead resistance of your test leads by touching them together and them subtract that from your 1095 reading, but I doubt it will contribute much.

hth

Thanks Dan

Reference Bracket - 8 mm washer pictures ?
 

... Ugh.. I found the answer to my question below at:

Gap answer and picture ! http://forums.pelicanparts.com/porsche-911-technical-forum/245180-3-2-ref-sensor-flywheel-sensor-questions.html

Regarding "
-if you have to remove the bracket put the old sensor back in and tape a 8 mm washer on the end of it. Then bolt the bracket back in. The washer will make sure that the new sensor is at the correct spacing.
-Pull the old sensor back out and put the new ones back in.
Also if you do a search there is a thread with pictures showing you how to do it. "

Ok, I need to pull the bracket, can someone direct me to the pics on the 8mm washer trick mentioned ? :)