Anyone replace a M50 knock sensor?

[Russell]

My peake tool indicated a code 45 for a problem related to the knock sensor for cylinders 4-6 on my 95 525i M50tu.

I wonder what the impact would be? For example does it go into a retard condition? Car seems to run fine. I use 93 octane with my EAT chip.

My Bentley says thay can be replaced without removing the intake maniford. A quick search of the archives did not reveal much "what/why or how" except I might have to remove the intake mainford. TIA

[Jon K]

Well the code (is it a check engine light or just a code?) may not be that its failed, but that it registered knock. Mark advances the timing a good bit so if you get a crappy tank of 93 it will definitely ping. If thats the case, and the knock sensor detects it, it'll store some faults and yeah its probably pulling some timing.

If the sensor itself is bad (kind of hit or miss, they're passive sensors so they don't usually go bad very often) then its simple to replace. You can replace the front one (between cyl 1 and 2 or 2 and 3, I forget) without pulling the manifold but if you don't know what you're looking for I'd recommend pulling the manifold its really easy. The back one would be a challenge with the intake on. Not impossible at all, but harder than the front one. It could be a stored code from eons ago - who knows. Reset the computer and see if it comes back!

Oh, its probably easier to access them from below if you have a lift or ramps. But still, removing the intake is worlds easier.

[Russell]

Jon,
Thanks for the help. It is a code, not a check engine light. I deleted the code a few weeks ago. Just rechecked today. I will delete it again.

So it just might mean it just deteted a ping due to bad gas and not mean a failure of the sensor? Bentley seems to be very limited help.

[Jon K]

Yeah it could be bad gas, or it could be the sensor. Do you hear any pinging or hesitation under high load low rpm? Not low, but lets say midrange maybe 2000 - 3800 rpm? If you have any pops or "tat tat" noises its pinging, if not, it could be the sensor. They're not that cheap unfortunately but a lot of guys just get used ones from yards because they rarely fail. Check with Winfred I bet he has some.

[Russell]

Thanks Jon,
Good advice. I think I will see if I can make it ping obove 2,000 rpm under load such as up a hill.Harder to do with an auto. May just put it in a higher gear in manual mode.

I may also have my indy look it over and see if the Peake is giving me accurate info and if I have an issue. Car seem to run fine with very good gas mileage. I can get about 30 on the highway.

[Russell]

Noticed no knock under load up a hill, 2000 plus rpm in manual mode and set in drive. Perhaps all is good,even with knock sensor issues, as long as I use 93 octane. Wish I understood what my Peake actually measured, a ping or a knock sensor related issue?

[Jon K]

Russell if you're reeeeeaaally concerned - pull your spark plugs and get a macro photo of each tip. It'll give me a good idea of how the car is running and should show any signs of detonation should they be there. Pic has to be relatively up-close and focused.

[Russell]

Jon,
Thanks