S50 Swap CEL Knock Sensor Help

[Chuck6902]

I have an S50 swapped into an e30. I did the swap last year and replaced both knock sensors at that time. Car ran great other than I hated the lightweight flywheel and 4 puck clutch for daily driving in traffic. Over the winter I pulled the motor/trans to replace the flywheel and clutch (I went from a lightweight flywheel back to stock). Upon reinstall I got a CEL and was throwing a knock sensor code for cyl. 4-6. I pulled the manifold and replaced with a new sensor and I still have the code. I can't hear any pinging coming from the car but at or above 3K rpm the CEL comes on. The car seems to be running fine with no hesitation, etc. It generally goes off once it drops below 3K but occasionally stays on. I've rechecked all of the connections and all the other sensors are new (ie intake air, water, etc). I am at a loss. Any insight would be appreciated.
Thanks....

Bump

[Chuck6902]

bump

[Patrón]

it's my opinion that the sensors are super sensative and no matter how new/fresh they are, the s50s almost always give the code and the flash of the check engine light.

[Jrdeamicis]

I know I replied on another forum but here it goes.

Check the Crank position sensor. 580ish (or somewhere near it) or 1280. There is very conflicting info on the reading of that sensor. If I remember correctly (which I could be wrong) Pin 1 is ground, Pin 2 and 3 is signal. If you can get an oscilloscope on it that might be a good way to see what the signal is doing.

What happens is the CPS is strong enough to make the car move @ low revs but above 3k it can not keep up and the ignition timing gets kind of wonky.

[hamlerda]

I would check and ensure that the actual sensor is bolted tightly to the block. Sometimes vibrations can give the sensor a false reading and trigger the light. If the sensor is too tight it can crack and also give false readings. Also keep in mind that cylinders 4-6 are close to the flywheel and clutch assembly which can generate vibrations that trigger the sensor.

[e21speed]

Any chance that you have the knock sensors plugged in backwards and that you needed to change the other one (1-3)? I think that I remember the plugs are the same so it would be easy to get the wiring mixed up and plug them into to the wrong connector.

[futureroadracer]

Did you ever fix this issue?

[LuxoM3]

How old is your alternator?

The S50 motor has some electrical gremlins. Even my 1995 M3 S50 got the dreaded Knock sensor CEL, even after TWO sets of replacements. I still got the CEL light once or twice a year for no real reason, usually starting from 1st to 2nd gear and turning left. Yes, turning left!

There was some discussion around it possibly being the alternator.

Curiously. When I upgraded to the Bosch 140amp... I haven't seen that light or code since.

So theory is, is when there's a voltage fluctuation, the ECU flips the Knock Sensor code for some odd reason.

Theory mind you.

[futureroadracer]

Interesting...

[gotKRAUT]

my e30 M50 is throwing the same code....still cant find the issue....did you have any luck?

i have a brand new 140 amp alternator....and my knock sensor puts the engine in limp mode and it wont rev over 3500 rpms till i clear the code again but it just comes back after a couple days

[bwh]

I'm getting the rear knock code as well on my OBDI S52 with all new sensors. Car seems to run fine with the exception of not revving over 6300. I've checked everything. It's odd since the car ran for 6 months just fine, then after I had the vanos changed it came on. I even bought a new sensor and it still comes on.

CEL comes on at approx 1800 rpm every time. No ping to be heard.

Checked the crank sensor, according to the Bentley, it should read 1280, but it shows 630. I'll have to find another crank sensor to verify the reading.

Checked a new sensor and it reads 580, so it's within the range of 10% per the Bentley.

[Stück]

I had been getting a knock sensor CEL on my OBDI S52 e30 and I changed them both out for new ones and nothing changed. I then went ahead and replaced the CPS.

Haven't seen a peep out of the light since.

[bwh]

I checked a new Crank position sensor today and it reads 580, which is within the 10% margin of my current one the Bentley says it can be, so I didn't bother buying it.

I'm running out of options. How can I tell which alternator I have? If I swao to the 140amp I want to make sure that's what I get...

The really confusing part is why the CEL doesn't show up with the stock 413 Red label, only with the chipped one.

[Stück]

For what its worth, my bad crank sensor ohmed out fine too. It wasn't.

[bwh]

Damn, I guess I'll just have to buy a new one and see.

[Balthazarr]

Damn, I guess I'll just have to buy a new one and see.

Yeah, the codes, while helpful, aren't completely accurate every time.

[bwh]

OK new crank sensor. Still have the rear knock sensor code. The common thing about all this is the code doesn't come on until the rev's hit 1800 or so.

I thought it might be the vanos unit advancing the timing too fast, but I disconnected the vanos solenoid and rear knock sensor code still comes up.

[Balthazarr]

OK new crank sensor. Still have the rear knock sensor code. The common thing about all this is the code doesn't come on until the rev's hit 1800 or so.

I thought it might be the vanos unit advancing the timing too fast, but I disconnected the vanos solenoid and rear knock sensor code still comes up.

Well, if it's the Voltage fluctuation/spike as Luxo says, then maybe the voltage reg/alternator is to blame.

[united323is]

I know this may sound basic, but make sure you didnt over torque it, the torque spec is really low(5-14 ft-lbs if I remember correctly) If it is over torqued or near the upper limit it will make the sensors more sensitive. At least that is what i was told repeatedly in my time as a BMW tech.

[bwh]

The sensor itself it at the right torque; I used a torque wrench to make sure.

I'll have to disconncet the alternator and see what that does. thanks

[scooper]

bumping this old thread...Any new revelations on the CEL? Knock sensors or CPS otherwise?

Has anyone used the OBD2 sensors and spliced them into the OBD1 harness?

[5OnTheFloor]

A few people have done it

http://forums.bimmerforums.com/forum...7&postcount=17