Running Without Maf
 

Hi MB friends,
My CLK 430 1998 some days ago showed my a lack of power between 4000 and 6000 Rpm, i ma not used to run the engine at this RPM but i noticed a bad gear change at this RPM.
The car showed code P170 and 173 so .......i decided to clean the MAF, but before connect it again i did a test without and tahe car is running really well, change very smooth and also the lack of power is disappeared...ICREDIBLE.
I think that the ECU has some recovery program or use some default value for timing and air temperature....
Does anyone know more about this function?
I connected again the MAF and the car is running better than before but without MAF is more powerfull.
Many thanks
Alberto

With the total lack of input the controller does take remedial action. In some cases there is also a MAP sensor for back-up in others the fuel computation is made from the throttle switch.

With the defective part in the system poor reading are accepted although a correction program does repair them for the basic conditions to a limit. The 4-6000 rpm run usually catches a bad MAF as its not a normal condition and it is a condition where the value being monitored (air flow) is at the max.

Your car has probably the most compensation of any modern car. It can add up to 32% fuel to the normal mapped calculation. I worked on a 2003 Lexus this last week where the customer had spent $13k for a turbo kit with trans mods and the car consistantly pegged the fuel trims at idle (looked like a diesel). I verified the capabilities on the Lexus tech site and long term fuel trim was only 20%.

My 2000 BMW 540 only has available 25% fuel trim. Many others only have 15%. The 32% used in the late MBs will almost correct anything.

many thanks
 

many thanks Steve ,really usefull help.
Alberto