Subject: 540i Crank sensor problem: A note on Crank sensors Author: e34jef : member since December, 2007 : 119 posts Posted on: 2008-01-28 08:16:13

I had this problem with a 540i: right at 4500rpm the engine would stumble badly, not be able to rev past 4500 and flashed the MIL. Fault code was always Crank Sensor. I replaced it twice with new parts from Pelican.
Convinced that this was a fuel delivery problem I replaced filters and the fuel pressure reg, gas lines, and removed/cleaned injectors all with no improvement.
The Bentley Manual states that the resistance of the CS should be 540 +- 10% for a six and 1280 +- 10% for a V8 crank sensor. I checked both the Pelican sourced parts and they were 535 and 554. I had the right part number on both parts, but decided in desperation to try a dealer sourced part. The part from the dealer was 550 ohms. I decided to buy it anyway.
I installed the dealer part and the 4500 rpm flameout condition left for good. A reboot according to board member "shogun" resolved the shift point hesitations and cleared up the rough idle. This car is now prefect!
So, the Bentley is WRONG about the resistance data of the two crank sensors and the Pelican sourced part is defective from new.
Why is that part defective?
here's a pic of the two, Aftermarket is black part on left:






You can see that the "north/south" relationship of the magnet in the aftermarket part is NOT FULLY EXPOSED to the tone wheel on the crank and that the magnet is only a small stub sticking out. It also does not fit into the mounting hole snugly.
Compare the original BMW part on the right. The "north/south" relationship of the magnet aligns with the blades of the tone wheel, so at high rpm there is no fade of the signal.

Lessons from the story: Consider buying genuine BMW parts whe those parts are critical!
I bought two Pelican sensors @ 45 bucks each plus shipping. The dealer part was 114.00. Also add in the fact that I probably replaces fuel system parts that didn't need replacing and the dealer part was cheaper.

• 540i Crank sensor problem: A note on Crank sensors (pic) - e34jef 2008-01-28 08:16:13 (1110 views)
  • Re: 540i Crank sensor problem: A note on Crank sensors - stellar11 2008-01-29 18:59:19 (197 views)
    • Re: 540i Crank sensor problem: A note on Crank sensors - e34jef 2008-01-29 22:09:58 (189 views)