1999 CLK keeps on misfiring !!

[maxxie]

Hi all
Thanks to anyone reading and sending comments !
I have a 1999 CLK200 (no kompressor), 276000 km, with a misfire problem going on for months now. I have searched this forum and found a user (Plugs-SLK200 (R170)) with exactly the same problem on the same engine. His problem seems to be solved but mine still isn't.
Every time the car runs fine it only takes a day or 2-3 before it starts misfiring again, pulling away and while rpm is less than 2000 the engine misfires with explosions in the exhaust system. At acceleration after every deceleration, with rpm < 2000 it misfires, the lesser throttle the more problems. Above 2000 rpm and highway it runs fine.
First spark plugs have been replaced, afterwards, spark cables, afterwards one coil and new spark plugs, afterwards new coil moved to other old coil, nothing helps.
From the Trond post I learned spark plug can get waste very quickly, in a couple of days, but I don't understand by what.
Another thing I learned is that bad radio reception is connected to electrical issues of a car as well, I believe my reception isn't as good as it used to be but I don't know if there's a connection to the problems I have. The last thing I tried was to follow advice from this site : Bosch F8 DC4 gapped at 1 mm. It ran fine for 2 days (500 km).
Diag. shows only misfire fault code.
If anyone could help in answering these questions :
- What can I do next ?
- Can I measure some electrical value some place, eg resistance, voltage ... that would lead to a solution ??
- Does the decreased radio reception ring a bell ??

Thanks to you all in advance.
Kindest Regards,

Nico

[joe p]

I take it this has a ME controlled M111 engine.


If it does I'd be looking hard at coil cooling oil leakage, wiring harness deterioration and bad crank reference sensor signals (bad sensor or metal buildup on it)


This is not a familar model to me.



Joe

[maxxie]

Yes, its'a M111 engine.
I noticed this morning, while driving a piece of bumpy road that suddenly the bad behaviour was gone, very good response to the throttle and accelerating a lot better. It only lasted a few seconds.
So the question is : could it be an electrical connection, loose or dirty cable plug ??
The misbehaviour is gone everytime new plug are installed but what in heavens name makes the plugs only last a couple of days ? The last time I tried F8DC4, gapped at 1 mm. (saw that in a reply to a guy with the same problems on the same engine in a Norwegean SLK 200 with no kompressor).
Again it's getting worse by the day.
Any ideas ????????
Thx,
Nico

[manny]

While NOT an expert on this subject, I would have the engine idling & start a " wiggle test ".
Just pull & wiggle every wire gently & listen for an rpm changes, misfires, etc..
The fact that the engine smoothed out for a brief period when you hit a bump sure would suggest a loose/bad connection.

[joe p]

Look long and hard at the engine wireing harness.



Joe

[maxxie]

Hi Joe, Manny and all others,

I did spend quite some time checking for vacuum leaks and bad wires/connectors. Yesterday I disconnected all connectors to ECU and sprayed all of them with contact spray. I waited for about an hour an reassembled. Now the car has lost ALL of its performance. Idle is good, hitting the throttle gives enough rpm but when under load it's awful. Today I checked cable from sensor in exhaust (labmda ?) Four wires are in a steel harness that is in a rubber harness. I checked at the place were the rubber harness shows 2 cracks, where it bends to go inside plastic cable guide. I could slide rubber and steel backwards and was able to feel the 4 wires, was able to pull a little to see if one of them was broken but they seem ok. I measured at the connector (sensor disconmnected) with an ohm meter, all combinations on the 4 wires but couldn't measure a thing. IS THAT NORMAL ?
I drove the car today, twice, for an hour, highway and noticed I somtimes have full power available, but only for a very short period after I turn the ignition key off and on.
Has any body ideas when reading this ??
Thanks again.
Nico

[dkveuro]

Hallo.
My way to tackle this problem with 260,000 plus kilometers on the clock would be to do the following..........
Take a master gauge pressure reading of the oil pressure to make sure it is correct .
Very high pressure indicates a bad oil pump relief valve and high pressure would pump up the hydrulic lash adjusters lifting the valve(s) of the seat causing a back fire in the manifold/exhaust and a dead miss. (Especially with weak valve springs.)Am finding some vehicles with over 200 psi oil pressure when cold and up to 300 psi with bad oil pump relief valves. Especially VW's........
Next check cranking compression and a leak down test.
Looking for a maximum of 10% leakdown.
Also look for weak or broken valve spring(s), this will cause all sorts of weired problems on a CPU controlled engine.
Also might check the voltage output and a ripple test . Am experiencing problems with some vehicles when a/c ripple is over 0.600 vac.
Although this might not uncover your problem this will eliminate otherwise simple things that can account for symptoms you are describing.
dk

[maxxie]

Hi all,
Yesterday another dealer managed to diagnose the care (not that obvious, it's been converted to LPG, mototmanagement does not respond without certain measures) and the airmass sensor was replaced. It runs perfectly on fuel now but the LPG system keeps on giving the failure led and switches back to fuel. Question that remains is if the airmass sensor got worse slowly causing the missfires. Diagnose did not give any other fault code so now I have to find out what the problem with the LPG is.
Regards from Belgium.
Nico