R170 SLK230 Rough running under load

[ColinPT]

Hi All. My first post on this excellent forum. Unfortunately, although I've learned a great deal about 'other things' here, I have an issue of my own which remains unresolved.
My SLK230 R170 has had just about everything replaced to try and stop an irregular running / misfire problem. Plugs, leads, supercharger (ouch!), MAF; and still the issue remains. Drive below 60 (2k rpm) and it's smooth. Increase to about 2,200rpm and the engine starts to run rough - like a weak mixture. It is more noticeable if you hold a lower gear at high rpm, say, 3-4k. In this scenario it is almost like a plug breaking down, randomly missing a beat. Heavy throttle can sometimes cause the 'miss' but otherwise the car goes like a rocket. My trusty mechanic has all the electronic analysis gear and cannot find any fault - no OBD codes at all. He suggests the only answer may be to put the motor on a rolling road. M111 engine 56k miles, FSH from new. Any thoughts would be appreciated.
Regards to all, Colin.

 

[streethawk]

Hi All. My first post on this excellent forum. Unfortunately, although I've learned a great deal about 'other things' here, I have an issue of my own which remains unresolved.
My SLK230 R170 has had just about everything replaced to try and stop an irregular running / misfire problem. Plugs, leads, supercharger (ouch!), MAF; and still the issue remains. Drive below 60 (2k rpm) and it's smooth. Increase to about 2,200rpm and the engine starts to run rough - like a weak mixture. It is more noticeable if you hold a lower gear at high rpm, say, 3-4k. In this scenario it is almost like a plug breaking down, randomly missing a beat. Heavy throttle can sometimes cause the 'miss' but otherwise the car goes like a rocket. My trusty mechanic has all the electronic analysis gear and cannot find any fault - no OBD codes at all. He suggests the only answer may be to put the motor on a rolling road. M111 engine 56k miles, FSH from new. Any thoughts would be appreciated.
Regards to all, Colin.

Hi have you made sure oil is not getting on the maf as it does sound like the maf. Was it a Bosch maf as all others are kak and fail.

 

[ColinPT]

Hello Streethawk
MAF is genuine Bosch and both MAF and pipe work are spotlessly clean.

 

[streethawk]

Hello Streethawk
MAF is genuine Bosch and both MAF and pipe work are spotlessly clean.

Hi really sounds like it needs to go on a star with someone that knows how to use one properly! You could be spending money on parts you don't need so at least putting it on a star you will get some answers hopefully.

 

[martyz]

coil pack? could be fuel related,filter restriction,fuel pressure,leaking fuel hoses from fuel pump(common) can you smell fuel?

 

[ColinPT]

My thanks to Streethawk and Martyz for your responses. I am trying to find someone local to the Notts area who has rolling road and diagnostic facilities. No luck as yet. Streethawk - you're right, I don't want to keep throwing money at it.. I'm more interested in finding someone who can diagnose rather than replace! Martyz - interesting comment re fuel - I can't smell any fuel while running or stationary, but when I get out of the car (obviously close to fuel filler point) I can smell fuel fairly strongly. I've looked but can't see any leaks in or around the filler or anything dripping to floor, so dismissed this as nothing more than normal?
Regards

Colin

 

[Ade Vic]

If anything like the clk the is a small overflow tank by the filler neck with a return pipe to the main fuel tank with age this pipe can split and you can get the fuel smell pipe is located behind the wheel arch liner easy diy to replace

 

[ColinPT]

Thank you Ade Vic. I'll have a look tomorrow!

 

[ColinPT]

Update. I have managed to find someone who has the means and knowledge to help. He has road tested the car and is of the view the issue is fuel related. He's having the car next Friday to clean tank, fuel lines and injectors and check electrical parts. I'll let you know how I get on.

 

[ColinPT]

Update: If you are following this thread you may be interested to know what further investigation has shown. Complete engine diagnostics/fuel system/electronics have revealed nothing - everything working correctly with no error codes etc. However, the mechanic has road tested the car and is confident the problem is the 'non standard' exhaust system, which he believes (confidently) is restricting gas flow and indeed causing back pressure at higher revs. With the roof down at speed you can hear the exhaust whistling and popping. The rear boxes are not original and appear to be a custom job. I have ordered an OE rear exhaust section, which is coming next week. Fingers crossed!

 

[ColinPT]

Sorted

Well. Who would have thought it.. the cause of my 'misfire'.. the gearbox. It failed a month ago and inspection revealed water contamination to the point the fluid represented strawberry yoghurt. Mega bucks later after a complete rebuild it drives brilliant. The gearbox guru said the gearbox and torque converter were in a bad way, most likely causing the electronics to go haywire. NOTE - check your auto fluid for contamination.. save yourself a great deal of money!!

 

[streethawk]

Well. Who would have thought it.. the cause of my 'misfire'.. the gearbox. It failed a month ago and inspection revealed water contamination to the point the fluid represented strawberry yoghurt. Mega bucks later after a complete rebuild it drives brilliant. The gearbox guru said the gearbox and torque converter were in a bad way, most likely causing the electronics to go haywire. NOTE - check your auto fluid for contamination.. save yourself a great deal of money!!

Glad you have sorted it. Trouble with these mercs is some engine faults can make the gearbox feel at fault and also gearbox faults can feel like engine problem. I changed my trans fluid last year and keep a regular check on its condition as I brought the dipstick. You should have a sorted motor now then, fingers crossed