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Thread: S50 Camshaft Sensor code after head gasket replacement

  1. #1
    Join Date
    Jul 2004
    Location
    Indianapolis
    Posts
    141
    My Cars
    '86 E30S50, '12 VW GTI

    S50 Camshaft Sensor code after head gasket replacement

    I’ll start from the beginning briefly. I have an E30 S50 swapped car that blew a head gasket on track in May. I’ve since replaced the gasket and other typical wear items like hoses and gaskets while I was in there. It’s primarily a dedicated track car that was a ground-up build and the motor has less than 10k miles. So it’s a very clean car in the engine area...no corrosion, dirt, etc.

    Since I put it back together, my OBD1 code reader keeps picking up this pesky Camshaft Sensor code. The car will rev freely in the garage, and even allow SLOWLY taking the revs up high on the street. However, when driving if you give it moderate to heavy throttle, the engine abruptly acts like it cuts spark or fuel entirely and then backfires out of the exhaust. I will note that my wideband O2 is indicating it’s idling a little lean. When driving, the AFR seems normal, though.

    Here is what I’ve tried to fix the issue:
    1. Replaced camshaft sensor with new OEM.
    2. Re-timed the engine/Vanos.
    3. Replaced crankshaft sensor with new OEM.
    4. Swapped DME with a spare.
    5. Checked cam sensors harness wiring.
    6. Cursory check and spray for vacuum leaks.

    I’m stumped. I’m not a professional, so I suppose it’s possible that I messed something up on the timing...twice. However, I’m using the proper tools, and I marked everything when I disassembled it. I also don’t have access to a smoke machine to check for vacuum leaks, but I’m not even sure if that would cause the camshaft code to pop up.

    Am I missing anything?
    Thanks!





    Sent from my iPhone using Tapatalk
    -Brandon
    '86 325es S50
    '12 VW GTI Autobahn
    '03 540i M-Sport (sold)
    '08 Jeep SRT8 (sold)

  2. #2
    Join Date
    Jan 2002
    Location
    outta SoCal, now CO
    Posts
    1,212
    My Cars
    '98 M3 Alpine White
    Two reasons for the CPS codes: Either the ECU doesn't see the sensor or there is a timing mismatch between the cam and crank sensors. It may or not be OK during idle but when the VANOS does it's thing the timing difference between sensors goes bad or out of tolerance, or could be the other way around, bad at idle, out at RPM. You're probably a spline off. Need a 2 channel scope to verify.
    See ya later,

    tony
    '98 M3, '92 Dinan3, '05 R1100S BCR, '07 R1200S, Aprilia T

  3. #3
    Join Date
    Jul 2004
    Location
    Indianapolis
    Posts
    141
    My Cars
    '86 E30S50, '12 VW GTI
    Quote Originally Posted by tjm3 View Post
    Two reasons for the CPS codes: Either the ECU doesn't see the sensor or there is a timing mismatch between the cam and crank sensors. It may or not be OK during idle but when the VANOS does it's thing the timing difference between sensors goes bad or out of tolerance, or could be the other way around, bad at idle, out at RPM. You're probably a spline off. Need a 2 channel scope to verify.
    You’re probably right. When I re-timed the intake cam/Vanos, I adjusted it by one tooth to match a couple of good instructional videos I found. However, it’s quite possible that the exhaust cam is off a tooth.

    Thanks for the reply.


    Sent from my iPhone using Tapatalk
    -Brandon
    '86 325es S50
    '12 VW GTI Autobahn
    '03 540i M-Sport (sold)
    '08 Jeep SRT8 (sold)

  4. #4
    Join Date
    Jul 2004
    Location
    Indianapolis
    Posts
    141
    My Cars
    '86 E30S50, '12 VW GTI
    I finally gave up troubleshooting on my own and took it in to my local BMW shop. They’ve gone through and replaced the cam and crank sensors with Genuine BMW sensors. Apparently what I bought were OEM, not Genuine. They also verified the circuits are good all the way back to the DME.

    It’s still throwing a cam sensor code. Below are the cam and crank sensors overlaid on their scope. I’m not an expert at where they should be aligned. I’m wondering if this could show if I have the timing off a tooth...










    Sent from my iPhone using Tapatalk
    -Brandon
    '86 325es S50
    '12 VW GTI Autobahn
    '03 540i M-Sport (sold)
    '08 Jeep SRT8 (sold)

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