Engine Knocking

[lowleverage]

Hi All,
I have my W202 running for more than 3 years now and seems this problem still going on and on.
I'm using a W202 that is originally equipped with 1800cc engine (commonly found in Asia) but current engine that I use is 2.5L Brabus. The problem with this engine is that it keep on knocking.
I have replaced the gasket head (stil using original brabus gasket head), and did an overhoul on the block and found everything is working alright.
No scrathes in the cylinder, all parts inside are sound, while I did the overhould I also did a porting and polishing on the head cylinder.
But all of that are still in the tolerable area (0.5mm porting). Still, the knocking is not disappearing .
One thing though, my ECU is PMS (not the HFM), and the highest octane for gas here is around 95.

Are there anyone out there who has the same engine with the same problem as I have now?
Is it a mechanical problem or simply because this engine has to run with higher octane gas?

Thanks.

[Pagz]

Interesting! is it a 2.5L M111? or is it the I6?

Your knock problems will more likely be fuel or timing related,not mechanical that is unless you installed the cam timing incorrectly.

If your running a programmable ecu(PMS?) you should be heading for a dyno to have timing/fuel altered/checked and to check the system for faults like a poorly flowing injector or low fuel pressure etc etc

Cheers,
Paul

[lowleverage]

Hi Paul,

Yeah, it's M111 4 cyl 2.5L. The ECU is still a PMS (pressure management system) which is the common ECU for this car found in Asia in its early evolution (1994-1995?). I think my garage already installed all parts correctly.

As an addition, the knocking always comes when the RPM is at >5000.

I think this problem comes from ignition timing, but the problem as I'm aware is that for W202 maximum room for timing move is only 5 degrees in total which is not enough for my case.

[Pagz]

Ah!,
Ok so your system uses the usual Throttle postion + manifold absolute pressure + air temp sensor to control timing and fuel?

-I would verify all sensors are working as they should including the oxygen sensor.
-Check injectors and fuel pressure.
-Check the spark plugs are the right temperature grade.

Have you tried running a higher octane to see if that helps?

How do you know its knock?

Cheers,
Paul