Where is the crank position sensor and how do I check it?

Pretty sure lack of signal from CPS would set a code.
There is amethod for checking it directly from the OBD connector I believe (at least on my 91 240 I did it).
Got voltage? How about RFI relay on the fender?
Check it out in 700 FAQ.
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744-16v-4+OD 185kmi., 745-16v-4+OD 359kmi., 242Turbo-4+OD 170kmi?, 245DLT automatic 287kmi.. 245SE automatic 198Kmi.

You that I may be able to check my CPS from an OBD connector. What/Where is the OBD connector, and what is the method for checking it?
thanks,
Todd

Kinda came full circle after three weeks....

http://brickboard.com/RWD/index.htm?id=801498

Sorry about RFI relay, thought you had a 700....
Got a Bentley Manual?, highly recommended....
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744-16v-4+OD 185kmi., 745-16v-4+OD 359kmi., 242Turbo-4+OD 170kmi?, 245DLT automatic 287kmi.. 245SE automatic 198Kmi.

The crank position sensor sits directly above the bell housing, behind the engine. If by check it you mean test it, well, as far as I know you can only test by replacement with a known good unit. If the band near the connector end is yellow, it needs to be, or will eventually need to be replaced. The insulation on the yellow banded ones fail and the sensor subsequently also fails. Why do you suspect it is faulty? Becareful when removing the CPS, the aluminum housing is VERY fragile and can easily break. I cracked my housing when trying to remove it and had to drop the tranny to replace the housing bracket(that's the only way). However, once I replaced it, the car ran like a totally different car.

i have an 88 , i just changed the starter on it , afterwards it cranked and started fine,, i drove it , turned it of started it a few times on sunday ,, didnt drive it this week until i tried to start it today ,, cranks will not start/.. im still not sure where this CPS is ,, but it certainly seems like i may have damages it when i dropped the tail of the transmission to remove and replace the starter.. havent been abler ot see if the brick board has any photo references ?? any help?

You likely to not have a CPS on you 1988.

u r correct, found out today
thanks

What were your symptoms with the bad CPS? I have a '90 that is hard to start, hot or cold, but as soon as it kicks in, it runs beautifully immediately. Someone suggested that it might be the CPS, but I'm having a hard time understanding how a bad CPS would cause hard starts, yet show no symptoms when running.

The car mysteriously won't start, but cranks strong, after running fine all morning. After diagnosing per 700/900 faqs and Haynes:
1. No Spark
2. Coil o.k.
3. Timing Belt o.k.
4. Fuel pump runs with key on, but I can't hear it when cranking- this may be do to the fact that the cranking drowns out the sound of the pump, though. I also ran a jumper at the fuse panel for the pumps, and still no start.
5. I do have gas in the tank.
6. I checked the diagnostic codes: 1-1-1 no problems.
7. I replaced the Power Stage.
8. Still no spark.

I have nearly resigned to towing it to my mechanic, but I realize that the next step may be the CPS. This one scares me though, as I have heard that they are very brittle.

Thanks for your response,
Todd

Your hard understanding is correct, they do no fail inthat manner, some is just guessing, not the best way to diagnose.

I had occasional hard starting, and eliminated virtrualy everything else step by step. Finally I replaced the CPS - the engine was transformed. They do get old, and so does the wiring leading to it. If it is getting on a bit (mine was 10 years and 300,000 miles old) replace it - they don't cost much.
Spray WD40 etc over the bolts and leave for several days.
Loosen the bolt. It is hard to get at - you need a small socket set with a flexible drive.
Try waggling the sensor. You can tell before you have got the bolt out whether the sensor is going to be seized in. If it won't budge, maybe think again. If it comes free - mine was loose- take it out.
For easier access you could drop the gearbox mounting cross member, but I managed it with nimble fingers.
Don't believe people who say they either work or not. They get old, tired and erratic, mostly in cold starting or sometimes when very hot.