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Thread: Position and Speed Sensors on Flywheel? - Euro 1983 635CSI

  1. #1
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    Position and Speed Sensors on Flywheel? - Euro 1983 635CSI

    Hello E24 gurus! Hope everyone is well during these times.

    I'm having a problem with my shark, hope you can offer some light: given I use the car more frequently during the weekends, sometimes not using it for over 2 weeks, I have a battery shut off switch.

    However, my mechanic found out that the switch was creating some type of short where a few things would remain on, despite the switch shut off, which would drain the battery nonetheless. This included the starter solenoid, which would heat up (although not engage) and once the car was warm, if I turned it off it would not crank again (solenoid would probably stick). Having removed the switch and fixed the solenoid, the problem was solved.

    All nice and dandy BUT, now when accelerating the car would stutter or "limit"once passed 4k or 4.5k RPM, having difficulty climbing the revs beyond that. Given all other things are in working order (pump, vacuum, injectors, etc.), I'm pretty sure the flywheel position or speed sensors are the problem. Probably the speed sensor, as if it were the position, car wouldnt even start.

    Certain that the sensor(s) are the problem, I took a multimeter reading of both: 1,024 Ohms and 1,017 Ohms. Would these reading be correct? Did the removal of the battery shut-off cable and switch cause some type of short on these sensors? If not the sensors, what else could be the problem?

    Appreciate any input. Thanks!!

  2. #2
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    Check this link. https://c8b88d8c-4698-4b77-b991-c1d2...0cc428edb0.pdf

    Scroll d own to page 33. There you will find the specs for the speed and ref sensors
    '84 Euro 635
    '88 M6 (Gone but not forgotten)

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    I made sure to completely isolate the battery so there was just one electrical cable from the battery to the cut-off switch, that then lead to the engine bay. This way you guarantee completely isolating the battery and power.
    1977 633 CSi RHD Euro. S38B38 3.9L M5 Transplant. 5 Speed Getrag Dogleg. 3.73 LSD. 417hp, 369lb/ft
    1971 3.0CS E3 2dr Alpina Special Coupe Racer, 347hp, 295lb/ft

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    The speed and cyl ref sensors go directly to the ECU, so I don't think you can harm them directly. They are merely magnetic pick up coils. What you might have done is bump or manage to dislodge one of the steel pegs mounted in the flywheel for the sensors to detect. Also, Did you possibly swap the connectors inadvertently? The sensors are the same put their positions relative to their associated connectors are important. Swap them up at the top and see if it makes any difference. Also, the connectors are brittle and can lose their tight connection to the main harness. Make sure the connectors have their locking wire still.
    '88 635, '92 325IC

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    I got those sensors backwards and the car started but that's it. IDK, perhaps the AFM arm needs to be tweaked?
    Rob E3

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    Thank you, EuroGeorge, Shipper, and carsnplanes! Based on multimeter readings, the sensors seem to be working. I think you have a good point there, carsnplanes: given my mechanic took out the starter by going underneath the car to help unscrew it (so as not to take apart the intake), he could've shoved the sensor(s). I'll book some time to verify that they are properly fixed to their positions next to the flywheel.

    I'll report back in a few days.
    Thanks!

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    I have changed my sensors and changed my starter. I can say they are far away from each other, ie I'm gonna say it is not the sensors. There are covers over the sensors also, making it difficult to tweak them accidentally. You can reverse them up top but the car won't get past 1500rpm if it even starts. Look somewhere else for the problem. Read the article/bulletin George referred to and make it a bookmark, it will come in handy now and in the future. I would also pull a plug and see if the car is rich or lean.
    Last edited by RSheiman; 09-22-2020 at 09:26 AM.
    Rob E3

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    I switched sensors (the one from position became speed, the speed one became position) to see if it would change anything—to see if one of them is the problem—but it didn’t. Last time around, this acceleration “stutter” was cured by buying new sensors, but these are now less than 6 months old. Everything else seems to work. I am wondering if it’s the harness to the ECU. Again, when I left the car at the mechanic, it was perfect. Once he did the service (fix starter solenoid and remove battery shut off cable) and I left the shop, the car does not pass 4.5 or 5k RPM. Feel like buying to new Bosch sensors as it would be an easy solution.
    Last edited by parlant; 09-25-2020 at 06:11 PM.

  9. #9
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    I've seen metal shavings and pieces of rust get stuck to the flywheel magnets of an engine and disrupt the magnetic field and affect the running of the engine. Just sayin.

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    Soooooo, follow up?
    Rob E3

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    Following up, I substituted the two flywheel sensors, thinking that they would be the problem but, hasn’t solved. Car continues to sort of “go crazy” once you hit around 5k RPM. Revs keep hitting something similar to a limiter, rev needle sways backs and forth and once you let off the throttle a bit, gears change and all back to smoothness. Basically, at any gear, you can’t get passed 5k RPM. I’m wondering now if it’s some electric connection from those sensors to the module, or a bad relay somewhere or bad connection to the module. Might need to take the car to an auto electrician to re-verify grounds, wiring, etc.

  12. #12
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    I would check the TPS # 21.
    If it doesn't send a WOT signal to the ECU,
    you won't get full fuel or timing.

    https://www.realoem.com/bmw/enUS/sho...diagId=13_0222

    TPS info starts on page 42.

    https://www.hpsimotorsports.com/motronic-

    Good luck.
    Last edited by 1986series6; 10-12-2020 at 07:18 AM.

  13. #13
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    + 1 on what Bob says above. I'm assuming manual transmission on you M635 so you should confirm idle and WOT inputs to your Motronic unit pins 2 and 3 respectfully.

    TPS.JPG
    Last edited by carsnplanes; 10-12-2020 at 08:01 AM.
    '88 635, '92 325IC

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    Thanks guys! I’ll verify, but TPS is less than 6 months old. I replaced it as preventive maintenance. Car is a regular 635CSI with auto transmission (4hp22). 1982 build, 1983 model. I had this same problem a few months ago, I replaced the two sensors and it was fixed. I thought it was the same problem this time around so I replaced the sensors again, but this time no cigar. It’s something else, it seems. Either electrical connection from sensor to ECU, flywheel magnet, or something like that, I believe.
    Last edited by parlant; 10-12-2020 at 01:05 PM.

  15. #15
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    Quote Originally Posted by parlant View Post
    Thanks guys! I’ll verify, but TPS is less than 6 months old. I replaced it as preventive maintenance. Car is a regular 635CSI with auto transmission (4hp22). 1982 build, 1983 model. I had this same problem a few months ago, I replaced the two sensors and it was fixed. I thought it was the same problem this time around so I replaced the sensors again, but this time no cigar. It’s something else, it seems. Either electrical connection from sensor to ECU, flywheel magnet, or something like that, I believe.
    Ok, sorry, for some reason I had M635 on my brain when you said yours was a Euro.
    The TPS you have should have more wires on it(round connector). The TPS for the Autos have an internal wiper for throttle position information to the Auto tranny ECU. It also has idle and WOT info going to the engine Motronic. You may have replaced the TPS,but you should still confirm their proper inputs to the Motronic and Auto ECU.


    TPS to Auto ECU
    TPS auto.JPG



    TPS to Motronic
    TPS auto Motronic.JPG
    '88 635, '92 325IC

  16. #16
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    Even though the TPS is new check it's output to the ECU.
    @ WOP no signal goes to ECU for full tilt. Check as instructed in
    troubleshooting to eliminate the TPS as a possible problem.

    If you could check @ the ECU terminal, that would be the best source.

    https://www.bing.com/images/search?v...RST&ajaxhist=0
    Last edited by 1986series6; 10-12-2020 at 04:21 PM.

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    Not sure why you are hung up on the sensors, I think it is time to let them go.........................did we go thru the used ECU swap out? Not sure of the auto but the manual ECU's are cheap on Ebay, like 150 bucks. We all have an extra so when something goes wrong, we can swap out and eliminate it as the cause. I still think your AFM needs to be addressed. The carbon track wears. There is a DIY on changing the arm angle to move on a different location on the track, believe it written for Porsche but same thing. I found this

    https://www.youtube.com/watch?v=yQukm7lNux4
    Rob E3

  18. #18
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    Quote Originally Posted by RSheiman View Post
    Not sure why you are hung up on the sensors, I think it is time to let them go.........................did we go thru the used ECU swap out? Not sure of the auto but the manual ECU's are cheap on Ebay, like 150 bucks. We all have an extra so when something goes wrong, we can swap out and eliminate it as the cause. I still think your AFM needs to be addressed. The carbon track wears. There is a DIY on changing the arm angle to move on a different location on the track, believe it written for Porsche but same thing. I found this

    https://www.youtube.com/watch?v=yQukm7lNux4

    Appreciate the advice, RSheiman. In this case, the AFM is less than 2 years old, purchased directly from BMW Classic, so small chance anything would be wrong with it. Nonetheless, I do have the original one which was working fine so I can always swap it to eliminate that probability.

    Car works perfectly as long as below the 4.5-5k RPM mark so don't know if the ECU could be the culprit. I do not have access to a replacement ECU so perhaps getting another one from eBay, could also address the chance that there's something wrong with the original one.

    By the way, my shark has had a garage queen life and has been babied, before I got it: currently, it has 30k original kilometers (18k miles). So there's little wrong with it but electrical connections do get old...

    Re-checked both transmission sensors yesterday. Both above 1,000 Ohms so all good there.

    Today, I'll try to check whether the TPS is working properly, per previous suggestions from carnsplanes and 1986series6. I can also swap it for the old one, which was working fine, I've been told by PO.

    Thanks again for all the advice. Will follow up as soon as I can.

  19. #19
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    So you replaced all the expensive parts, what about the coolant temp sensor which is quite cheap. Also the cts connector is quite fragile and can crack. I'm just free thinking here.
    Rob E3

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    You must revisit the TPS and the ECU. If the engine runs up to the rpm you mention, the speed and reference are working.
    The only thing I could think of is the TPS is not sending WOT to ECU or the ECU is not responding to the signal.. It sends signals to the ECU for injector and timing.
    At WOP, no signal goes to the ECU and it will default to full timing and injectors.

    I wonder why just working on the starter would effect the engine rpm.

    So please, check the signal coming from the TPS and if the signal is correct, concentrate on the ECU.

    The info is on pg 40 of the link that Dr. George sent you.
    Last edited by 1986series6; 10-16-2020 at 11:14 AM.

  21. #21
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    Yes. rule out devices thagt are needed for full throttle. Easy to measure the ground needed for full throttle through the TPS to the ECU using the provided snips of the diagrams.
    The other need is fuel. Check that the FPR is working also. Check vac/loss of vac to the FPR and see if it responds accordingly. A leaky FPR will not retain the proper fuel pressure at the injector rail.
    '88 635, '92 325IC

  22. #22
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    Hello everyone,
    I have not had the time to test the TPS, unfortunately, but plan on doing so this weekend. One piece of basic information which I should have given earlier that might add some further color to the problem (sorry about this): on neutral, the engine will rev freely to up to redline. It is only when in gear (D, 3, 2, 1), that acceleration gets interrupted.

    Would this by any chance change conclusions related to TPS or any other sensors? Thanks again for all the valuable input.

  23. #23
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    Well now that changes a couple of things. Before I did my 5 speed swap,
    there were times when the auto would hic-cup on some upshifts. I never
    could solve the problem. It felt just like you said, hitting a rev-limiter.

    So we'll have to concentrate on how the tranny tcu talks to the engine ecu.
    What the connection is I'm not quite sure. But a connection there is. IMO.

    In the meantime, while I do some research I'm sure others with more
    knowledge than me will chime in.

    Maybe this will help. Look at page 2460-9, the test column "M" on the right.
    Has a WOT test for the TCU. May get some info from that. Looked for ETM for 83 Euro could not find.
    86 US best I could do, should be similar.

    https://www.millerperformancecars.co...g%20Manual.pdf

    Good luck.

    I'll take it that the ATF level is ok.
    Last edited by 1986series6; 10-28-2020 at 07:54 AM.

  24. #24
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    Ok, so, in an automatic car, the TPS works differently than a manual. In an Auto, you'll notice the TPS has 5 wires(round plug) as opposed to the 2 wires on a manual (Square /flat plug). Three of the five wires communicates to the Auto TCU for throttle position for load, downshifting points and cruise fuel and timing changes. It uses an internal wiper, rheostat with three wires for that. Two different wires communicates to the Motronic for only two reasons; idle and WOT fuel mapping. All wires can be traced and checked to their respective inputs of their respective computers. I suspect you have a fuel delivery issue if you are feeling hesitation in the WOT position only and only under load which you could only achieve in gear and driving under load. Free revving is not a good load check for WOT. So check that function of your TPS electrically. There is no TPS mid range feed info to the Motronic, just idle and WOT. The outputs of the TPS can be checked electrically with a multi meter right on the TPS.

    See my attached pics in the above thread for the TPS pin outs.
    '88 635, '92 325IC

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    F/U so we can learn!
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