E320 CE Misfire

[Kiwibins]

I have a 1995 E320 CE Coupe. Periodically she misfires. This problem is not at start up and infrequently unpredictable. What would the potential diagnosis be...........? Also does anyone have a good garage in SW19?

Tx

 

[ALAN@ECUCLINIC]

i work at a gge in se19
sounds like it could be a coil ,does it miss on 1 or 2 cylinders?
call me

 

[Kiwibins]

Thanks for the reply - champion. I will endeavour to listen tonight!

Greg

 

[television]

If it does it when warm it could be our old friend the ignition module loosing thermal contact.

malcolm

 

[allan l]

Greg, I had similar problems with my '94 E320 Coupe.
If I am right, your car is fitted with an M104.992 engine. This has a HFM fuel injection/ignition control system.
Part of the electrical ignition control cables (engine cable harness) run under the “valve cover”, above the spark plugs. It gets very hot in there. With time the cable insulation gets hard, particularly if the engine has been overheated.
When the cables are disturbed, say during a spark plug change, the insulation can crack, resulting in short circuits. This will cause engine misfiring and could damage your ECU.
The harness usually last about 10 years on W124s.
To check the situation, after removing cover, carefully check if the black moulded cables are very hard, brittle and cracked. If you intend to keep the car, I would get the cable harness/ignition leads changed, before they cause expensive problems, like blowing up the ECU.
Best of luck.
Allan

 

[Kiwibins]

Chaps

Thanks for the replies!

In response. The misfire seems to be on two cylinders.
Where is the best place to get replacement coils and cable harness/ignition leads? May as well change the lot to avoid future issues.

All the best.
Greg

 

[allan l]

Greg,
1. All these spares need to come from M-B.
2. Firstly check the condition of the cable harness, by removing the engine top cover. You will need to look at a Service Manual if you are not familiar with how to remove the air intake over the engine (like Haynes manual for 124 Series (their number 3253) and/or M-B E-Class Owners Bible1986-1995
(Bentley Publishers). If the cable harness insulation is still soft and not cracked, then it may still be OK. If not, consider getting it changed. You could change it yourself, but it has connections all over the engine compartment some very difficult to get at. I would use a specialist M-B, non-franchise garage.
3. If the cable harness looks OK, then I would start with the key parts simplest to change, like the suppressor plugs and eht leads which connect the spark plugs to the ignition coil packs ( there are 3 coil packs, each connected to 2 spark plugs). To get at these, you will need to carefully lift aside the cable harness (see Service Manual).
4. Do it step by step.