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  #1  
Old 11-19-2004, 10:59 PM
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Join Date: Oct 2003
Posts: 141
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

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  #2  
Old 11-20-2004, 08:31 AM
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Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
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.
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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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  #3  
Old 11-20-2004, 08:56 AM
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Join Date: Oct 2003
Posts: 141
many thanks

many thanks Steve ,really usefull help.
Alberto

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