BMW 3.0Csi D-Jetronic detonation problem.

Hello.

I am working on said car. No matter how i adjust the map-sensor, it gets ok AFR-values, but it still detonates. It has a new ignition distributor from 123ignition.nl, which is properly adjusted. The valve clearances is also perfect. This car has had a lot of work done to it, and i don't know if the head has been machined or something, but this should'nt make such problems, as long as the AFR and ignition timing is adjusted accordingly?

Does anyone have a clue about what might be the problem? Thank you in advance.

Hi Julian,

I can only seriously warn everyone to start (de-)tuning their MAP sensor. We have 3 screws and their setting is VERY SENSITIVE. If you play on one screw, you also influence other areas. Either part-load or full-load. Tuning is a matter of a few degrees of turning the screws.

Give it to a professional to retune and reseal it. And check vacuum whether it holds -0.5 bar long enough. Otherwise get you diaphragm replaces as well. You have to inform the tuner which ECU version you have. They come with no color code, blue and red. MAP sensors must have corresponding color codes or in case of red you should even use green for lead reduced fuels. If color codes are removed, you can still check via my ECU list in chapter 3.9. There must be an FD date code (month and year of make) on the ECU.

Hi Julian,

detonation into exhaust means unburned fuel into exhaust manifold. That comes from late ignition or too rich fuel. Those tuning screws are damn sensitive and you have to at least match 2 of them properly to have suitable AFR in all rpms and all load states. You should also check your vancuum level on idle to see whether you have false air.

Hi Julian,

what is the outcome?