Crankshaft pos/reference sensor

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trestontape
Posts: 8
Joined: Jul 04, 2022 5:57 PM
Location: Springfield, MO

Crankshaft pos/reference sensor

Post by trestontape »

I'm able to find sensors online, however, no sets that have a white connector and a black connector.
I have an 83 533i, with two sensors on the bellhousing. They have to be plugged into their correct slots on the wiring harness, and I'd like not to potentially damage anything if I plug them into the wrong place.
Also, what sensor goes where? Didn't mark them when I took them out- I know that there's a sensor with a white connector, and a sensor with a black connector.


Also, do M30B35 sensors work on an M30B32? I see some on eBay for 15$, not sure if it's worth cheaping out for.
Mike W.
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Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Crankshaft pos/reference sensor

Post by Mike W. »

First off, no, a B35 sensor will not work, it reads off a toothed wheel in front, not the flywheel

I don't think I've ever seen a color coded sensor for sale. Which is why I always make things with paint or tape. I know, a little late for that, but for future reference. Just hook them up, no harm will result if they're backwards, it just won't start. So if it then doesn't start, just reverse them. But you won't damage anything if they're wrong, it just won't start.
1st 5er
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Re: Crankshaft pos/reference sensor

Post by 1st 5er »

Mark one on both ends before pulling,
or replace one at a time.
trestontape
Posts: 8
Joined: Jul 04, 2022 5:57 PM
Location: Springfield, MO

Re: Crankshaft pos/reference sensor

Post by trestontape »

Mike W. wrote: Jan 02, 2023 5:00 PM First off, no, a B35 sensor will not work, it reads off a toothed wheel in front, not the flywheel

I don't think I've ever seen a color coded sensor for sale. Which is why I always make things with paint or tape. I know, a little late for that, but for future reference. Just hook them up, no harm will result if they're backwards, it just won't start. So if it then doesn't start, just reverse them. But you won't damage anything if they're wrong, it just won't start.

The car didn't start already, pretty sure this is my problem. Already replaced the wiring harness, checked for power to all accessories, they all work, and fuse block gets power. No fuses are popped and some of the relays click, just assuming everything else works.
Car does turn over, but no start. Both wires to the crank position sensors were melted, so they'd need replacement anyway.

I read somewhere that once there's a signal on both sensors, the fuel pump finally gets power. When checking for power to the fuel pump with both unplugged, there's nothing.
This leads me to believe that this will fix my no start condition.

Is this true?
Mike W.
Posts: 26936
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Crankshaft pos/reference sensor

Post by Mike W. »

trestontape wrote: Jan 02, 2023 6:02 PM
Mike W. wrote: Jan 02, 2023 5:00 PM First off, no, a B35 sensor will not work, it reads off a toothed wheel in front, not the flywheel

I don't think I've ever seen a color coded sensor for sale. Which is why I always make things with paint or tape. I know, a little late for that, but for future reference. Just hook them up, no harm will result if they're backwards, it just won't start. So if it then doesn't start, just reverse them. But you won't damage anything if they're wrong, it just won't start.

The car didn't start already, pretty sure this is my problem. Already replaced the wiring harness, checked for power to all accessories, they all work, and fuse block gets power. No fuses are popped and some of the relays click, just assuming everything else works.
Car does turn over, but no start. Both wires to the crank position sensors were melted, so they'd need replacement anyway.

I read somewhere that once there's a signal on both sensors, the fuel pump finally gets power. When checking for power to the fuel pump with both unplugged, there's nothing.
This leads me to believe that this will fix my no start condition.

Is this true?
Not exactly. I believe when the starter is engaged the fuel pump will receive power, but it definitely will not if the car isn't running or at least cranking. And a little quirk of the system is the ECU has to see both sensors on startup, but once running it only needs the speed sensor, not the reference sensor. Simplistically speaking, the reference sensor tells the ECU where TDC is, but once it's running the speed sensor keeps track of timing by the flywheel teeth.
RetiredDoc
Posts: 1316
Joined: Feb 12, 2006 12:00 PM
Location: Aiken SC

Re: Crankshaft pos/reference sensor

Post by RetiredDoc »

I played the crank but no start game for several months. Installed new speed and reference sensors, swapped them, etc. The problem turned out to be the reference pin had fallen out of the flywheel. Not bent, not damaged, but gone. The speed and reference sensors need that pin. It is supposedly quite rare to lose one on a manual tranny, which I have. I opted to replace the flywheel rather than trying the repair approach since the clutch had over 200K known miles on it. BTW, I never found the pin. Despite the rarity, I’d recommend rotating the flywheel and making sure of the pin on yours.
LarryM
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Joined: Feb 01, 2008 11:40 AM
Location: SoCal

Re: Crankshaft pos/reference sensor

Post by LarryM »

RetiredDoc wrote: Jan 02, 2023 8:40 PM I played the crank but no start game for several months. Installed new speed and reference sensors, swapped them, etc. The problem turned out to be the reference pin had fallen out of the flywheel. Not bent, not damaged, but gone. The speed and reference sensors need that pin. It is supposedly quite rare to lose one on a manual tranny, which I have. I opted to replace the flywheel rather than trying the repair approach since the clutch had over 200K known miles on it. BTW, I never found the pin. Despite the rarity, I’d recommend rotating the flywheel and making sure of the pin on yours.

Do you happen to have any idea what would have caused the reference pin to come loose and fall out? I'm kind of concerned I may have the same situation.

I recently changed my starter motor, using a correct factory reman'd Bosch B34 unit. I've driven the car since installation and it ran fine, but since then it sat for several weeks and suddenly I have a no-start with no spark to plugs. Main relay and coil check out OK. I think it's either one of the sensors (one of them suddenly went bad on my E24 years ago, with the same exact symptoms) or possibly the new starter in some way knocked the pin out of the flywheel...however I think that's unlikely.

Bad time for this to happen; I'm having knee surgery tomorrow and it'll be quite awhile before I can get under the car to take a good look. I've owned the car for over 10 years and it's never failed to start, but that's life for ya. While I'm recovering I get to agonize over this situation.
jc72
Posts: 710
Joined: Aug 16, 2010 11:52 AM
Location: Oakland, CA

Re: Crankshaft pos/reference sensor

Post by jc72 »

Try bypassing the OBC imobilizer by jumpering two wires going into the box under the steering column. It’s a known failure point that prevents starting like you described. If you search on here you’ll find detailed instructions.
Mike W.
Posts: 26936
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Crankshaft pos/reference sensor

Post by Mike W. »

As retired doc said, it's very unusual for the flywheel tab to come off a manual car, but it's not that unusual for it to come off an Auto car. Not quite common, but it happens. So, once your knee allows, it might be worth crawling underneath the car, pulling the stiffener between the engine and tranny and checking to see if it indeed has come off.
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