1996 W202 C280 Misfire (M104)

[Will]

Hi Gang,

Spoke to an old friend of mine the other day. He has a 1996 C280 that his wife uses and has owned for 4/5 years now. Last week it developed a misfire and he was asking for anything obvious to check before taking it somewhere.

I popped over to have a quick look yesterday evening. Aside from the basics it hasn't had a proper service since they bought it (circa 60k with full history), now on about 75k. A lot of that will be town driving and shorter journeys.

He'd already got a new set of Bosch plugs for it as they hadn't been done in years. I swapped the plugs over for him, even if not the cause of the problem they were well due to be changed.

Old plugs all looked pretty similar, quite sooty and worn but nothing exceptionally bad. After careful replacement the car ran as before, starting and idling largely ok but definately misfiring still and down on power when driven. Tried disconnecting the MAF sensor earlier as well to see how it ran without - aside from a subtle change in idle speed it still misfires as before.

At certain revs (say 2-3k) it sounds largely ok but not as smooth as it should be.

Before he takes it in somewhere or we have another quick look over it does anyone have any suggestions? I would have suspected a coil perhaps but it seems as though it is not specific to any one plug (or pair of plugs) as they all looked so similar on removal.

Haven't seen or heard much of this on W202s in the UK but are they affected by the dreaded W124 M104 loom problem by any chance?

Will post back when I've had time to have a better look

Cheers,

Will

 

[d w124]

First of all,good to see you as it`s been a while .Do check the coils first but since is an m104,well you know the rest

 

[kth286]

If it was a coil gone you would notice immediately because it would be on 4 cylinders and difficult to drive.

It is likely one cylinder and that points to the extenders under the 3 coils (between plug and coil).

They contain 2K ohm resistor wires which go very hard and brittle because of the heat, and the flexibility to extend to make contact with plug top connection is lost, thus firing on 5 cylinders.

Previously about £10 each (x3) from dealer.

Be very careful when moving the ignition wiring due to it's brittleness.

It can also be beneficial to also replace the other 3 plastiky connectors on the end of the ignition wires.

Reading the codes of course will show which cylinder the faulty one is.

 

[Will]

Thanks guys.

It does seem quite a noticable misfire once you go to drive it, my friend says it is difficult to drive and very low on power. He/they also mentioned that there was a quite noticable smell of rotton eggs from the exhaust (cats).

I also initially suspected a coil or lead issue, but bearing in mind that the plugs all looked pretty similar it didn't point to an obvious issue with one or two cylinders only.

Almost as if it is a mixture control issue - perhaps running extremely rich on all cylinders or similar, or an issue affecting the ignition on all coils/cylinders.

I have been away for a couple of weeks holiday and also very busy in general recently so have recommended a good local MB indi (1-2 miles away from him) who should be able to look at any fault codes and have a better look for him at some point soon, at least to diagnose if nothing else.

Will post up with any more details when I know but if anyone else has any suggestions I'd be keen to hear.

Cheers all,

Will

 

[kth286]

perhaps the lambda probe has died completely and the feedback to computer for fueling is asking for more.

The codes will reveal all.

 

[EDZ649]

Do these suffer with the engine loom problems too?

 

[BlackC55]

Yes they do!

 

[grober]

Don't know but the smell of rotten eggs from the exhaust points to something going on with the catalytic converter. Might be partially blocked [internals collapsed] or wonder if the smell is due to sulphur compounds being "washed out" by extra water in the exhaust which might point towards- dare I say it----- a CHG on its way out.