Knock sensor code 143

I recently did a did a B230FT swap into a 1990 240 all went well except I am getting a 143 code. I drove it all day yesterday and did not get the code, I have also found that I only get the code when the engine is cold and It revs it up to about 3-4K.

So basically if I start the car and allow it to warm up I can beat on it and not get the code, if the engine is cold or not warmed up yet and and I can't even pull out of first gear with out the code popping up. I also find the engine stumbles and runs rough on a cold starts, but starts right up with no issues.

So far I have swapped out knock sensors and it didn't do a thing. Filled up on high test and put 200 miles on. no change.



In case it matters I used the engine and computers out of a 1992 740 turbo.


If anyone has an idea please be sure to chime in asap, I will be working on the car today and it would be great if I can get this issue worked out.

How tight did you tighten the knock sensor bolt onto the motor? Too tight can cause it to feel too much knock. Did you check the wiring make sure it's good to the ECU from the sensor?

sbabbs said:

How tight did you tighten the knock sensor bolt onto the motor? Too tight can cause it to feel too much knock. Did you check the wiring make sure it's good to the ECU from the sensor?

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How tight exactly I am not sure, I am not one to over torque things like this but I will go out and back off it a bit and see if that helps any. I'll just snug it down.

I just tried to retard the timing a bit on the distributor although I heard it makes no difference. The engine should be cool enough to try again as it seems to only do it if I start it and take off driving while its cool. So I will back off the knock sensor and try that as well before I try it again.

Wow just went outside , engine was cold started it up took off just as I have been doing to get the code to pop up and punched it .....no code popped up........

The knock sensor seems a bit tight when I loosened it, it was not excessive but took enough force to where I hand to palm the wrench and use caution not to bust my knuckles, I re-tightened it using two fingers. Wish I didn't do both the dist timing and snugging down of the sensor cause it would be interesting to know what it was, but I am happy no light popped up so I'll leave it be. Thanks for the quick advice I think it was the snugging that did it for me.

When the motor is cold they tend to have piston slap which is a knocking sound. It's pretty normal and goes away once things get warmed up. Could have been what your overtightened sensor was picking up with the cold motor.

There is a specific torque value for the knock sensor, I don't have the manual here to look it up but if it is too tight or too loose it won't work properly.

Make sure you have the correct plug on there, not the EGR one. Ask me how I know....

Torque settings according to the green books

Early style p/n 0 261 231 006 --> 8ft.lbs
Later style p/n 0 261 231 046 --> 15 ft.lbs

Those Bosch knock sensors are surprisingly durable. Contact plating tends to corrode, especially if the gasket on the plug is missing.
Do you get the code under load or or not?