SLK320 Slight Misfire - Mercedes Benz SLK Forum

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#1 Old 06-23-2015
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SLK320 Slight Misfire

Hi folks, just wondered if the community can offer any advice regarding a slight misfire on my car.

It's a 2000 registered V6 320, and the misfire is very subtle- mainly on light throttle or on initial pick up (I also think the idle isn't a smooth as it should be). However, under hard acceleration or load the car pulls like a train and doesn't miss a beat, and there is no check engine light on.

I have connected up a scanner and there are no fault codes logged at all, so as a precaution I have replaced the spark plugs (they were due this year anyway according to the service history), but this has made no difference.

Has anyone else come across anything like this before?

Any help or advice would be much appreciated.
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#2 Old 06-23-2015
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#3 Old 06-23-2015
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Hi Jeff, Thanks for the quick reply- that's something I had never thought of, and as the car has done nearly 140,000 miles a system clean out is probably well overdue!

I'll have a look at some reviews as to the best product we have over here and definitely give it a try- I'll post the results.

Thanks again, Martin.
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#4 Old 08-22-2015
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How did you get on with your misfire ? My 2000 320 had a bit of a flutter on tickover just floored it to overtake a tractor and now has has a full blown misfire
Regards Stuart
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#5 Old 08-22-2015
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Plugs, wires, coils. All things to check. Plugs and wires are routine maintenance items. Coils can be moved around to see if that is the issue or not.
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#6 Old 08-28-2015
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Originally Posted by t140v View Post
How did you get on with your misfire ? My 2000 320 had a bit of a flutter on tickover just floored it to overtake a tractor and now has has a full blown misfire
Regards Stuart
Hi Stuart, sorry to hear about your troubles. I'm afraid I haven't managed to get to the bottom of my problem yet, so far I have replaced the spark plugs, fuel filter, MAF sensor and tried a bottle of forte fuel treatment in the tank, but at the moment the misfore is still there.
I have just paid to have it professionaly diagnosed by a specialist who has the correct diagnosis system, as the scanner I used did not pick up any error codes (but then again I have never had the managemant light come on), the only thing he identified was an error code relating to the crankshaft sensor. He checked all of the coil packs and plugleads and gave them a clean bill of health and also recalibrated the MAF sensor and various other settings on the engine. He told me that these engines are very prone to either vacuum or air leaks, but said that mine was absolutley fine.
His final diagnosis was that the amount of wear in the dual mass flywheel might be causing the crank sensor to give the ecu innacurate data, thus causing fueling or timing issues. He has suggested that I try replacing the dual mass flywheel and possibly the crankshaft sensor next.
So I am just trying to get some more info as to whether or not to carry out this work. The problem I have is that the parts will cost me about Ł800 for aftermarket items, and probably double that for genuine Mercedes. Coupled with the fact that Mercedes UK have only sold one flywheel in the last 12 months, makes me think it's not a common fault. However, there does appear to be play in the flywheel and there is a certain amount of rattle from the transmission on idle, so there probably is an argument for replacing the clutch and flywheel. I would just like to be more certain that it is this problem that is causing my misfire before I commit to spending this amount of money to fix it.
Hope this helps you out in some way Stuart, amd best of luck.
Martin.
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#7 Old 08-29-2015
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Afternoon Martin,

When I went to the car the next morning it started up ok without the constant misfire from the day before but still had the slight flutter.
I had ordered a bottle of the Chevron Techron concentrate and have added that to half a tank of petrol the engine now seems to be running smoother and does not develop a misfire now when I give it a good boot.

The crankshaft sensor causing uneven running has popped up in a good few posts that I have read, loose securing bolts and dirty connections can cause uneven running, for the cost of a new sensor (about Ł20 ) I might change mine just to see the effect. Hope that's all that's wrong with yours.
MERCEDES BENZ SLK 320 2000 TO 2004 CRANKSHAFT PULSE SENSOR | eBay

Regards Stuart.
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#8 Old 09-24-2015
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Replaced the crank sensor Martin, thst seems to have sorted all the problems I had
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