W124 230E auto (1990)
I have a cold running problem. The symptoms are:
Engine starts as well as ever from cold but by the time I’ve started to drive away there’s what would seem to be a severe misfire. This is more evident when trying to accelerate when moving or pull away from a stop. When running at a constant speed it’s somewhat smoother but as soon as the throttle is opened the misfire/judder is evident. After a few miles of running it completely disappears & the car runs & pulls away from halts very smoothly.
This started a week ago on a cool & wet morning so I thought it could be dampness & gave it the WD40 treatment – same problem the next morning. I then cleaned the distributor cap & rotor arm (cap rotor & leads replaced 11 months ago), cleaned the contacts of the various sender units at the front of the engine etc; I put in new spark plugs (old ones looked fine) – problem still remained.
On Saturday I drove 180 miles (problem there for the first few miles then it ran perfectly). Returning home after 6 hours it ran rough from cold again (hot running was fine) – now there was certainly no dampness in the engine 6 hours after a 180 mile trip!
I’ve just taken the air filter case off & checked & cleaned again all the wires & contacts I could see – problem still there!
The only thing I did find was that one plug lead had rubbed on something causing a short length to be rubbed flat (about a 1mm of rubber removed). The strange thing was that the lead either side of the rub mark was ‘swollen’ to a noticeably larger diameter. I’ve seen leads rub before but never swell. I moved the lead well away from the engine (I’ll get a new set today). Problem remains.
When the engine is running cold (& rough) I’ve tried removing each plug lead in turn – the engine runs equally even worst no matter what lead is removed – so the problem is not related to a particular cylinder. There’s a single pin sensor with a long black plug right on the centreline of the engine just in front of the air filter case – when this is removed the engine again runs even worst (actually this applies hot or cold) so I assume that is working.
To sum up – the problem only occurs between a cold start & to reaching something approaching normal running temperature. I tend to think the problem is related more to fueling than ignition but I don’t know what to look at next.
Any help would be very appreciated.
Regards
Russell
I have a cold running problem. The symptoms are:
Engine starts as well as ever from cold but by the time I’ve started to drive away there’s what would seem to be a severe misfire. This is more evident when trying to accelerate when moving or pull away from a stop. When running at a constant speed it’s somewhat smoother but as soon as the throttle is opened the misfire/judder is evident. After a few miles of running it completely disappears & the car runs & pulls away from halts very smoothly.
This started a week ago on a cool & wet morning so I thought it could be dampness & gave it the WD40 treatment – same problem the next morning. I then cleaned the distributor cap & rotor arm (cap rotor & leads replaced 11 months ago), cleaned the contacts of the various sender units at the front of the engine etc; I put in new spark plugs (old ones looked fine) – problem still remained.
On Saturday I drove 180 miles (problem there for the first few miles then it ran perfectly). Returning home after 6 hours it ran rough from cold again (hot running was fine) – now there was certainly no dampness in the engine 6 hours after a 180 mile trip!
I’ve just taken the air filter case off & checked & cleaned again all the wires & contacts I could see – problem still there!
The only thing I did find was that one plug lead had rubbed on something causing a short length to be rubbed flat (about a 1mm of rubber removed). The strange thing was that the lead either side of the rub mark was ‘swollen’ to a noticeably larger diameter. I’ve seen leads rub before but never swell. I moved the lead well away from the engine (I’ll get a new set today). Problem remains.
When the engine is running cold (& rough) I’ve tried removing each plug lead in turn – the engine runs equally even worst no matter what lead is removed – so the problem is not related to a particular cylinder. There’s a single pin sensor with a long black plug right on the centreline of the engine just in front of the air filter case – when this is removed the engine again runs even worst (actually this applies hot or cold) so I assume that is working.
To sum up – the problem only occurs between a cold start & to reaching something approaching normal running temperature. I tend to think the problem is related more to fueling than ignition but I don’t know what to look at next.
Any help would be very appreciated.
Regards
Russell
