CLK 320 missfire / running rough

[TWOBARROWS]

I don't believe this. 2 new Coil Packs, I drive to work, it starts running rough again so I stop & disconnect the connectors to isolate which cylinder is failing, it's #4, I have to stop at least 6 or 7 times on the way to work & back & it's always pot #4. Got home, took the new good working coil from pots 2 & 3 & put it in posn. #4 & 1, then put the previously good Bosch coil (originally from 4 & 1) in pos. #2 & 3 thinking these are all known good working coils that have been proven. It's still playing up, pot #2 now! This can't be a coil problem, I just don't believe I can have a new failing coil & a previously known good coil suddenly fail.
I have noticed that before the cylinder is switched off the car starts to run a bit rough, & now I am listening, I can hear a 'tinny pop' or two, I guess that is the misfire. Is there anyone out there who can help explain how this poxy ignition system works please & why it fails in this manner. I can only think that there is somehow a 'weaker' coil that somehow causes this symptom, although the coil itself is not at fault? HELP, PLEASE!!! !!!.

 

[Alex Crow]

hello. firstly, not using genuine bosch coils is not ideal - sorry to say this now you have spent your money.

right, do you have the system with 2x coils, 2x HT leads+caps and 2x HT caps under the coils? if you do i suggest you might have a problem with either a lead or cap. keep swapping them round until you can determine if it is a coil, cap or lead - or possibly not related to ignition at all.

 

[TWOBARROWS]

I'd just thought of the caps under the coils actually, need to go swapping again!
I went for the cheaper coils as the Bosch ones don't seem to be that good either, both mine have cracks & coil failure seems to be so common!
I still woould like to understand better exactly what is happening here!

 

[Alex Crow]

easy enough to understand, at high temps (it gets hot under that cover!) the insulation properties of the caps/coils/leads change, as do their resistance. at some point there becomes an easier path to earth for the ignition voltage than the electrode gap in the plug. when this happens you naturally get a missfire. you correctly understand the resultant cylinder shut down in post #17 above. your method of swapping things around is simple but effective, stick with it and keep us up to date.

 

[TWOBARROWS]

Went to swap the HT caps (the bit under the coil) and noticed on was dirtier than the other, went to clean it & it started falling apart! Upon closer inspection it looks like one has been replaced already, personally I would have replaced them as a pair seeing as they are rubber (ish) in a very hot evvironment! Off to the nearest Merc dealers it is then.......

 

[TWOBARROWS]

Swapped them anyhow & poodled off to Purslows Guildford, ran like a dream! New HT thingy (eight pounds plus vat) in pot 4 & original coils back in, runs sweet. Hard to believe such a pathetic little bit of rubber has caused me so much hassle.
Anyone need a pair of coils, going cheap?

 

[swiggo]

can any one help me i have a clk 200 elegance 1998 with 119000 on the clock and my car keeps making a noise like plastic breaking think its missfiring also my car has loss of power when i put the accelorator to the floor my car starts to slow down so i have to let it off then put it on again i have changed the maf sensor and changed the spark plugs and air and fuel filter please help

 

[swiggo]

can any one help me i have a clk 200 elegance 1998 with 119000 on the clock and my car keeps making a noise like plastic breaking think its missfiring also my car has loss of power when i put the accelorator to the floor my car starts to slow down so i have to let it off then put it on again i have changed the maf sensor and changed the spark plugs and air and fuel filter please help

 

[TWOBARROWS]

Do the sympoms disappear if you turn tha car off & on again?

 

[zxrichie]

Hi
everyone.. Sorry to resurrect this thread, but i thought this would then go to the original participants. Well i have exactly the same problems as "Dave1966" and "Twobarrows" (Plus a load of other guys when i googled this problem). I shall go down the route of checking the HT leads, coil packs , plugs etc.. (might be a while but i'm not in the best of health) However i have a couple of points i need clarifying. A lot of discussion has gone on about the MAF, after looking on ebay etc it shows the MAF as either the 3" long black plastic tube in the air inlet route, and a sensor that looks like a big USB key. so when we are advised to replace the MAF, Which is it?, also unplugging the MAF can help the diagnostic, can someone explain how? and what do you unplug, do i take out the whole unit?

Just a few things i need clarifying on.

Cheers

Rich

 

[rpe2]

If you go to Eurocarparts, the bosch unit is £170 (and you'll get 25% off with the forum code). Please don't buy a cheap ebay copy, else you'll be buying another next week.

If you can remove the sensore from the housing, a bosch agent may be able to supply a replacement if you supply the part no stamped on the side.

 

[zxrichie]

Well, interesting answer..i take your advice about purchasing a Bosch unit as opposed to an ebay one. However, What unit..plus can someone actually answer my questions!! or say you dont know.

Rich

 

[rpe2]

Charming response.

If you look on the ecp website you will see it will be the unit incl the pipe part, you will need to phone a Bosch agent to see if they sell the insert as a separate item.

Unplugging the wire from the maf may put the engine onto a default map, if it runs better unplugged, then the maf is likely to be duff.

You could of course spend a small amount of money on diagnostics.

Over to you now...

 

[zxrichie]

Richard, i'm sorry if my reply came over as "charming", it was not my intention. It was born out of weeks of frustration with the car and other things, wrong place, wrong time etc.. sorry. I'll have a go at unplugging it and see what happens, do i unplug it when its running rough or when its running okay..?

Rich

 

[zxrichie]

Right then, got some "results"...
started up the car and it ran "normal", well normal to me anyway.. I then pulled out the connector to the MAF and the following happened.
1) The engine carried on as it was idling as before.
2) The fan unit started up and got faster and faster and sounded as if it was about to take off.

These were the 2 only noticeable effects of disconnecting the MAF sensor. So does this indicate a failed unit?

Cheers

Rich

 

[zxrichie]

Hi All, sorry for not posting sooner but i have sorted out this problem which should help anyone else who "bumps" into this problem. After being advised by plenty of sources far and wide, i decided NOT to go down the route of replacing plugs/coil packs/HT leads. Not only because of the cost involved but i just didn't think they were the problem. So my attention turned towards the MAF. Once removed , i cleaned with the Halfords cleaner and Bingo, the improvement was stunning. it still played up a bit, so i ordered a new one, put that in and i now have my old car back.

So, Check the MAF first, its cheaper and it just might save you a lot of grief and hassle.

Rich

 

[Pathfinder]

I experienced all of the above including fitting a new MAF and in the end it turned out to be a cheap little vacuum pipe that was drawing in air !

 

[mercenaryali]

My W208 CLK 340 Convertible - sat for about 6 weeks in a dry garage. Battery disconnected.

Returned home, reconnected the battery, started first turn of key, reset windows, steering and
soft top mechanism. Drove up the road a few miles, returned home and handed keys to wife.
She got about 2 miles up the road and the car started misfiring, stuttering and losing power.
After replacing a raft of items: plugs, plug leads, fuel filter, O2 sensors, coil packs
- I could go on however it actually turned out to the the Mass Airflow Sensor.
New one is around £50.00. Drives like a new car - the moral of this story is:-
Check the easy items FIRST - the MAF sensor is right there in plain view.

Happy driving all Mercedes Men . . . . and of course Ladies !

 

[ajlsl600]

Seen it many times before, new battery frys the air-mass sensor, also jump starting causes this fault,

Welcome to the forums!

I had exactly that on. My w208. Found out after! That one should put lights blower ect on before starting when fitted d with new batt.!!! To avoid frying maf another great bit of design