After spending £130 + new air cleaner with MAF Shop in Berlin the new MAF is now installed and the result is ........... only a slight improvement! :-(
Possibly that might be an understatement because I've not had to chance to take the car a long trip yet. (That will be this weekend). Perhaps the fuel consumption does look better but the 'misfire' is still there and the MIL dashboard light is still lit.
My first reaction is annoyance with BMW who, to be honest, I'm sure are no different to any other manufacturer. Why don't they disclose the real meaning of the codes! And I mean the REAL meaning of the error code. Would it undermine their business to disclose what analysis the control unit is performing to generate the exception. It seems that they have been forced to comply with international regulations to provide a standard method of reporting but they have only reluctantly complied!
So the investigation continues. It's interesting that
- After resetting the light with Torque it illuminates almost immediately after the engine is started. There is some initial diagnostic taking place that is checking various parameters and finding them out of limits.
- The misfire/rough running occurs around the time the turbo is beginning to work and is generating positive inlet manifold pressure.
This is now making me suspicious of the EGR operation despite the fact it has been cleaned and now seems to operate freely instead of being carboned up. What I have to find out next is how and when the valve operates. I know it's vacuum operated and I know where the electric solenoid valve is. But is it operating correctly? My suspicion is fuelled by the fact that the misfire seems to occur at 1800rpm which, as I understand it, is about the time the EGR valve is closing due to the inlet pressure being greater than the exhaust gas pressure.
All that said I'm still suspicious of the volumetric efficiency curve. This is calculated by measuring the theoretical air flow through the engine using inlet pressure, inlet temperature and rpm and comparing it against the measured air flow. The ratio of the two is the volumetric efficiency.
I'm surprised that the maximum recorded value when the turbo is working is still less than 100%. (I'll try logging when the car is being driven rather than sitting on the drive). The second 'anomaly' is why the dip around 2500rpm?!
