I'm searching mercedes forums non-stop looking for info but I figure I'll throw this out at you guys.

I bought the car used 3 months ago at 26K miles. Its always had this problem for me.

When accelerating anything more than light acceleration, at around 1800-1900 rpms, about 20 mph, the car loses acceleration. Power just goes away. Then a second later it kicks back in and everything works fine. The problem is very consistent, whether the car is cold or warm or the acceleration is medium or hard. It seems only very light accel avoids it.

A mercedes forum had a guy with the same issue, no one could resolve his problem, but they mentioned something about variable cam timing and how the second cam kicks in around that point, and to make a long story short it made no sense but I figured I'd toss it in here for you guys.

The problem does not seem fuel related since the car runs fine and accelerates fine, its just this blip at this one exact point. Its not a sputter either, its a full 1 second cutout.

Just FYI, I've replaced fuel pump, spark plugs, intercooler pump, oil change, tranny fluid/filter change since I've had the car. I have a needswings intake but thats only for the past 2 weeks. Also, the car pops and shakes a little at idle but that problem seems unrelated, and much more frequent in the MB forums. I'm investigating that too.

I have an IAT sensor and camshaft position sensor ready to be installed that I randomly bought for fun.... I just haven't had the time. (Camshaft sensor, not to be confused with crankshaft sensor)

I have a spark testing light ordered that apparently I can point at a spark plug wire while the car is running and it will tell if the wire is working. Never used one before, should be interesting...

The chances of this small community helping me with this strange problem is pretty slim compared to the larger mercedes community but I wanted to post it up anyways just in case someone knows or if someone has a similar problem.

 

I can,t help you. But I wanted you to know this small community will smoke the help you would get at that other site. Just sit back and watch.

 

Did anyone use an OBD scanner to check for fault codes? It could point out your problem.

Also, don't forget the throttle control circuit. With all of the variable between the pedal and the throttle blade, I'm suprised we don't have MORE unexplained problems.


The 1 second power loss sounds like what happens when the Traction Control engadges. You don't get the traction control light flashing in your face when it happens, do you?

 

I have the same thing happen, but it's usually under mild acceleration and dosen't happen too often. I just figured it was the SC clutch engaging. I firgured it was the added load on the engine to turn the SC. I never noticed the TC light coming on, but my RPMs do drop...maybe by about 500 or so.

 

Same here, mild acceleration then stomp the pedal with give that minute delay and go. It has something to do with the TC, SC, or tranny shifting down. It won't happen at the track from a launch. Never has. If you spin then that's a different story.

 

Some form of traction control makes sense... But when I spin the tires the TC kicks in and lights flash. For this normal acceleration there is no spinning, at all, and no TC light. Could TC still kick in consistently at the same exact RPM if there were a problem with the TC system? has that ever been heard of with these cars?

It definately seems like its something 'intentional' the car is doing, and not mechanical.

But I can consistently give light medium to hard acceleration (not close to tire spinning though) and get the car to cut power at 1800-1900rpm/20mph for about a second.

 

From a stop, shift into 1 and accelerate lightly-mildly watching your RPM’s. If you feel the same delay around 3k RPM as you do between 1.5-2 when in D, it’s your SC engaging.

 

Oh yeah and about checking for codes, I've never had a CEL so I haven't bothered checking. If I have time Ill stop by autozone and see if they see any codes.

And srt6 gang member thanks for the tip I'll try that today.

 

The supercharger is turned on as you approach 2000 regardless of the throttle setting. I am getting a video together to put this myth to rest for all time. I hope.

A suggestion is to pull the fuses for the traction control. Pushing the button is not all inclusive and there is still some parts of "HAL 9000" operating, there are posts documentating this to search on.

It seems to be a speed related issue as compared to RPM, this needs to be determined. Try starting out in the W position versis the S position, Summer / Winter to see if the speed or revs dictate when you see this repeatable hiccup condition.

Well be looking for feedback, additional data points; Enjoy.

WOODY

 

I'm going to have to say it has zero to do with a "second" cam kicking in, as we only have one and there's no variable timing.

Just from reading it I would suggest TPS. Similar problems with a faulty Sprint Booster. You can get a new Throttle Body with sensor for about 300.00, it may also be the one at the pedal. I'd start there.

 

As it has been mentioned it does take about .5-1 sec(never timed it) for our s/c to kick in if your in normal drive mode and you stomp it. If its already reved up in the gear you want to be in this will NOT happen. Will it do it if you have the car in 1st gear 20mph and stomp it? Also is the TC coming on? That will shut you right down for about a sec.

Maybe you can ride with a buddy with an srt6 and see if his does the same.

 

To eliminate the supercharger being associated with this problem simply disconnect the electrical connector to the SC and see if the problem persists.

 

Good ideas guys. I'll try all of this on the way home from work.

And from memory I believe if I have been moving, and slow down, and punch it while still moving, there is no blip in the acceleration. Maybe it is the supercharger kicking in....

I'll report back later.

 

(IMO) I don’t think the SC is engaged all the time but I do think it is on all the time. When you start the car, the SC turns on as well. It only engages when one or multiple parameters are met, then the ECU will engage it. Those parameters could be a certain RPM or MPH or throttle position or speed of acceleration or a combination of all.

You will only notice the SC engaging under light-mild acceleration in first. This feeling comes in D between 1.5k-2k RPM and in 1 around 3k (this is for un-moded ECU’s). If you floor it from either D or 1 you will not notice the SC engaging at all. Also, if you’re out of 1st gear you will not notice it either because your speed masks it or it's engaged already.

Group test, everyone w/o a mod ECU follow the tips in post (7) and report back when you feel the SC engage. If I’m wrong sue me but my Internet lawyer is here too pursued you not to .


Looking forward to your video .

 

The only test I've really done is driving in 1st. There doesn't seem to the power loss in the same spot.

I've been too dead after work to go through step by step and do multiple tests. I'll follow a plan tomorrow.