cracked knock sensor

[Dr Shuffles]

I'm in the middle of replacing my starter and all the coolant hoses. Fun times.

I removed the rear knock sensor (so I could get better access to one of the starter bolts) and in the process I cracked its housing. Or maybe it was already cracked, I don't know. Should I get a new one? I don't want to order a $60 part and wait until it arrives, but then again I really, really don't want to deal with removing the lower intake again.

[1996 328ti]

Personally I'd replace it since it's out already.
I just don't see any point in not replacing a questionable part when you already have it out.

I don't know if you can find a genuine BMW sensor for $60.

I have one in my garage I never used.
I'll sell it it for $60 which is more than I bought it for just to have it get used.

12 14 1 734 580

[Dr Shuffles]

Yeah, that's what I figured. I already ordered two new sensors (I noticed after posting that the other one had a crack in it). For all I know, the black plastic is just for decoration, and the sensor still works fine, but I'm not gonna take the chance.

If this was a $10 part, I wouldn't even have asked.

[1996 328ti]

FWIW, I was getting knock sensor faults and my forward one was cracked.
Replacing the sensor didn't fix the problem.

But it's such a PITA to replace them, might as well do it.

While everything is apart, any leaks around your oil filter housing?
And vacuum hoses to your injectors look good?

[Jayrockstar]

Getting an error code for the knock sensor for 3-4 (rear). Any chance I can change it out without removing the intake Manifold?

[Dr Shuffles]

Originally Posted by Jayrockstar

Getting an error code for the knock sensor for 3-4 (rear). Any chance I can change it out without removing the intake Manifold?

I never tried it, but it seems like you may be able to reach it from the front if you remove the alternator and the oil filter housing.

[Jayrockstar]

Thx.. Will update if successful...

[xxxJohnBoyxxx]

Originally Posted by Jayrockstar

Getting an error code for the knock sensor for 3-4 (rear). Any chance I can change it out without removing the intake Manifold?

No I don't think you can do it without removing both upper and lower manifolds. I think you have to replace both sensors since they are one piece with both sensors using one plug to feed their information to the DME (M44 only), the M42 has separate plugs for their respective bank of cylinders (Thank you Dr Shuffles for correcting me on this). Also the front sensor is behind a solid coolant pipe.

It would be a good time while you are in there to replace the rear head coolant pipe since these break with age and are one of the top reasons for a major over heated motor which will warp or crank the head or at a minimum blow the head gasket due to the aluminum head expanding much faster then the cast iron block when a bad over heating event happens.

Good luck and I'm interested to see if you can do the Knocks without removing intake manifolds.

Best, John S

[Dr Shuffles]

I think you're right. There's a photo here showing the knock sensors with the coolant lines in place. It looks like it might be theoretically possible to get the rear one off without removing the hoses or the IM, but it's not worth it.

The M42 and M44 have different styles of knock sensor. On M42, they're two separate units, each with its own plug. On M44, they share the same plug.

[xxxJohnBoyxxx]

Dr Shuffles thanks for the education, I learned something new today. I hate to post inaccurate information an I have in this post. I will correct it now.

Thanks, John S

[1996 328ti]

Originally Posted by Jayrockstar

Getting an error code for the knock sensor for 3-4 (rear). Any chance I can change it out without removing the intake Manifold?

I pulled the oil filter housing hoping I could gt to the rear sensor. No way.
BTW- My fault was caused by low oil. Yes!