MAYDAY! : C240 - engine barely runs after battery disconnect...
 

Euro 1998 C240 Sport Wagon - ME Motronic contolled all-alu , twin ignition V6

I dis-connected the battery in order to re-set the ECU since I was experiencing diminished performnace - ie; slugish acceleration, engine not pulling over 4K rpm, etc. All else ok.

I dis-connected and re-connected the battery, then re-started the engine : intitial start ok, then within 3 secs goes to very slow idle/barely runs. Acceleration pedal sollicitations have almost no effect. Car can ce re-started many times - no change.

I have to date :

- Checked fuel pressure at fuel dist ramp : ok @ 3.5 bar;
- Checked Air Mass Sensor with volt-meter - seems ok at 1v - 4v;
- Left key in on postion >5min to "re-train" throttle position;
- Dis-connected battery for over 20minutes, and closed elec. circuit by grounding pos. battery lead;

Please help : I am trying to avoid the local Benz Stealership and their $120/HR charges as well as a $200 one-way tow.

Any ideas ? I'm getting desperate... Thanks.

How many miles on it?

Had an almost identical problem with my C-280 (1999) I disconnected the battery for 1/2 hour, reconnected and the problems went away.

I tried that twice, even removed my ECU unit (to check part number) for well over an hour, so if it is a re-initialisation issue, Im sure that it's been disconnected long enough to reset the registeres.

I also tried to re-initialise the throttle bt letting the key set "on" for 10 min. then off then start: no change.

CORRECTION THAT'S 1998

It's got the all-aluminum, twin plug V6 but in a W202 chassis with factory delivered sport suspension, sport seats and small steering wheel.

I just wish it'd run right no w! :-((

Without starting the engine, turn the key to the number 2 position for 60 seconds. It may need to relearn the throtle end stops. See how this does and get back to us.

""Without starting the engine, turn the key to the number 2 position for 60 seconds. It may need to relearn the throtle end stops""

Thanks, but I already did that, twice. No joy.

Touch the ground/Earth to the Positive Batt+ for 10 seconds or more....with both leads disconnected from the battery...this does the trick on BMW's to reset to factory..It discharges the capacitors in the system and dumps the Adaptive memory .



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""Touch the ground/Earth to the Positive Batt+ for 10 seconds or more....with both leads disconnected from the battery...""

Thanks, did this twice too, no joy.

Try disconnecting your MAF sensor and see how it runs. If it runs better than I would think it is time for a bi-annual MAF senosr replacement. :cool:

"Try disconnecting your MAF sensor and see how it runs. If it runs better than I would think it is time for a bi-annual MAF senosr replacement"

Thanks, I did that and it stalls almost immediatly, as it should. I also checked it the "proper" way, that is with a voltmeter: all appears ok.

Just have to step on brake pedal to discharge any residule power.

Turn key Off for 10 sec , On for 30 for relearn and then start.

b
 

bump

After you have turned the key on engine off for 60 secs (only needs 30, but whats an extra 30), turn the key off and remove it. Let it set for a bit, 10 seconds is all it needs , but whats an extra minute.

If the car starts and idles then try putting (putting = 10-15% throttle) down the road for 5 miles or so. If you were able to loose the throttle adaptation you probably also lost the mixture adaptation. That wouldn't matter if the car (and air mass meter) were new, but if you have been running around heavily adapted and then you loose it the car will run like crap, till it reaquires the previous adaptation level. MB has the ability to add 32% more fuel than the original calculation, as needed. If it needed it and you removed it, guess what happens?

No telling how many other things now need resetting also. Disconnecting the battery is not a cool thing to do on late models.

Going back over your post indicates you have decaying performance issues before all this 'key off', etc, stuff.:rolleyes: .....would it be that the cat's are breaking up ?:1blank:
Need to do a back pressure test...no more than 2psi at 3000 rpm with about 1/2 psi increase as rpm's get above 4k..

Hmmmmm ?:confused:


.

It's Fixed ! Faulty Air Mass Sensor
 

IT'S FIXED : IT WAS THE AIR MASS SENSOR !!!

YOU GUYS ARE GREAT !!!

I replaced the AMS and , voilà everything ok !

EPILOGUE : The air mass sensor has probably been deteriorating over the last couple months, asq witnessed by the increase in gas consumption, stumbling at idle and poor acceleration.

The system was correcting the failing AMS through the ECU software. When the battery was dis-connected, the memeory was lost, the standard reset values were too far off to keep the engine running.

Thanks to ALL who helped !

SB thread was right on....

<<<If you were able to loose the throttle adaptation you probably also lost the mixture adaptation. That wouldn't matter if the car (and air mass meter) were new, but if you have been running around heavily adapted and then you loose it the car will run like crap, till it reaquires the previous adaptation level. MB has the ability to add 32% more fuel than the original calculation, as needed. If it needed it and you removed it, guess what happens?
<<<

Do you have a check engine light on? if so what codes ?

Adaptations reset
 

The fuel brain had adapted to a borderline maf meter. Those adaptations were reset with a disconnected battery.
You may have a bad maf meter. Driving the car may re-adapt.