Hi I wonder if anyone has come across this problem before. On a 2001 c240 the car starts and runs perfectly. When the car is driven with light throttle it drives perfectly, but when you put your foot down it doesn't pull cleanly as it should. There is no misfire or 'popping back' and there doesn't sound like the engine is suffering from fuel starvation. I own a garage and have a MB star tester and the are no fault codes logged in the memory. I have tried an air mass sensor but the fault is still there. I have spent 3 days trying to get to the bottom of this problem with no joy. Can anyone help
Regards

Kevin

 

Presume you are achieving full throttle? Have you done a throttle reset?

 

I have done a throttle reset and according to my star machine the throttle has a full range but I am going to check it visually....

With the ignition on and the airmass put to one side, and the elbow off the throttle housing, when we press the pedal to the floor the throttle butterfly seems to only open about 25-30degrees.

Do you or anyone else know if this is correct?

Thanks

Kev

 

Try driving it with the MAF disconnected. This will obviously throw a code after a few miles but it forces the ECU to run on a fixed set of maps and bypass the MAF. It should run fine without it.

The difference with part throttle and WOT is the car runs in closed loop mode during part throttle and open loop mode for WOT. So you have to figure that something is not right that the ECU normally compensates for in closed loop mode. So you could have a vacuum leak for example that's not bad enough to throw a fuel trim code because the ECU can compensate by adding more fuel, but bad enough so that it's running too lean in open loop mode. You seem to be well equipped, put an O2 sensor in the tailpipe, run it on a dyno (or just have someone really strong lift the rear wheels of the ground ) and see if it's running too lean at WOT under load.

 

I've never observed mine - if you know what I mean - listen to Buell - has vast experience

 

Where you able to figure out the problem with your c240? Mine is doing the same thing.