I recently bought a 2000 SLK230 Kompressor. I have a problem with it backfriring and sputtering during acceleration. It wasn't happening until I would hit 4400rpm, but the mechanic changed the crankshaft censor and now it happens at 4000rpm. The mechanic and a couple of dealership mechanics have tried everything they can think of. The car checks out nearly perfect on the computer and they've ruled out everything they could think of, like the exhaust. The Check Engine Light doesn't even come on. Under 400 rpm, the car runs great. My mechanic finally told me to take the car home and check this forum to see if anybody had some ideas what it could be.

 

Hi,

The car checks out nearly perfect on the computer. So what does nearly perfect mean? Does this equal NO CODES?

Under 400 rpm, the car runs great? I assume you mean 4000 rpm.

Mileage, service history, when problem started, Actions to date? A bit more info might help.

Is the CEL Check Engine Light working when you turn the ignition on? Surprised you have spluttering acceleration and BACKFIRE and no CEL illuminated.

I detect something that is not quite as it appears here.

Stuart

 

Yes, I meant 4000 rpm. There were NO engine codes at all. On the computer the Mass Air Flow sensor checked out ok also. The mechanic dropped the exhaust and it was fine. The problem persisted even with the exhaust off. Besides the exhaust sytem, he also tested the fuel pressure system, spark plugs, camshaft advance, and crankshaft position system. He installed a new crankshaft sensor and the only difference that made was that now the problem starts at between 4000 and 4100 rpm, whereas before it didn't start backfiring until around 4400 rpm. The car has 84,000 miles on it. I just bought the car a couple of weeks ago and the sellers consealed there was any problem. Let the buyer beware! Now they will only admit to "occassionally noticing that the car lagged a bit when getting on the highway," but deny ever hearing it backfire. So I really don't know when the problem started or what they might have had done. I also don't really trust their account of the service history on the car any more. So I got taken and my fiance is furious and all I can do now is try to get it fixed. But I can't even go after the sellers for fraud or file a claim under the purchase protection program I bought the car under until I can say what the problem is and how much it will cost to fix it. Additionally, the car does have a bad smell, like something burning, when it's backfiring, if that helps at all. To me it smelled almost like rotten eggs at one point, but my fiance said that was just the area we were driving through at the time, so I don't know.

 

1. (very important) Tell your fiance' to stop bitching; you have enough problems without her making your life a living hell. If you don't stop this nonsense now, it will only get worse BELIEVE ME!!!

2. Take the car to a dealer with a good reputation and get it fixed.

3. Rotten egg smell (AKA "day old beer fart") could be the catalytic converter.

 

Hi,
You did not reply to my question...
Is the CEL Check Engine Light working when you turn the ignition on?
Surprised you have spluttering acceleration and BACKFIRE and no CEL illuminated.

Assuming the answer is yes we need to start at the beginning.

I think will3hawks may have the right approach. Maybe you mechanic is part of the problem.

A misfire / spluttering acceleration points to either the fuelling or the ignition being incorrect.

Your mechanic has changed the CPS and taken off the exhaust but so many other things remain untouched / unreported. So can we assume basic engine systems like plugs, filters, FUEL etc are all OK?

My biggest concern is the fact that no codes are reporting.
A small misfire (that cannot even be detected by the driver!) will noprmally be picked up by the computer but you say no codes are set. Sure your mechanic is using an OBD scanner rather than an old fashioned Sun Tuner or similar. "Computer" is used to cover so many different bits of kit.

If the smell came from the exhaust it points to fuel. However i assume that this problem has persisted on more than one tank of fuel so once again assume the fuel is OK.
If there really are no codes I favour a Kompressor control system fault but this is just stabbing in the dark.

I still believe that there is something wrong here in the limited data we have been given.

Are you sure that the "new" Crankshaft Position Sensor was the correct type. Since this actually affected a change it sort of points to it being implicated in the problem. CPS faults are known to leave no Code record and are (engine) temperature sensitive. Is the car OK when cold but a problem when hot or similar.

Strange!

Stuart

 

Backfires usually point to an intermittent ignition issue. The scanner in use will not always pick-up the codes especially if your tech is using global OBD2 technology. Find a good euro tech with an auologic scanner or a factory mercedes scanner. The change in RPM suggests that the area (trigger from the flywheel) is possible however you may want to check the air pump check valve for a bad valve or pipe. The exhaust pressure over-rides the air pump pressurecausing a backfire at higher RPMs. No codes are stored from this concern. Hope this helps!! PS- This is a car forum, not Dr. Phils. REMEMBER: There are 3 storys- his, hers, the truth.

 

The scanner that I misspelled is an autologic scan tool. It is a PC based touchscreen laptop.

 

Hi did you ever solve this mystery problem as i have the exact same problem with my 1997 slk 230 and would really appreciate it if you could let me know if and how you you fixed it. Thanks in advance Steve.(teatime)