W210 E230 engine misfire under load

[TourmalineE230]

This is my first post to the forum. I have a W210 E230 Automatic (11.1995 delivery) with 178000 miles. Car has been well maintained over its life and is in regular use.

In recent days it suddenly developed an engine misfire. The misfire is only there when the car is in gear. When in Neutral or Park the engine idles normally and will rev up without any problem. But as soon as it’s driven it will stutter and wants to stall at idle. You have to coax it to get it up to normal speeds, and the misfire will clear intermittently as the car builds speed but you have to constantly modulate the throttle to ease the misfire. I initially thought the symptoms suggested I had HV ignition breakdown under load.

I made some initial checks and (despite my normal reluctance to just change parts without properly diagnosing first) I replaced the ignition coils and ignition leads after inspecting them and found a crack in the potted area on one coil plus one partially damaged ignition cable. However, the OE replacement parts I fitted have not altered the misfire one bit.

On digging into the issue a little deeper online, I saw several references to the dreaded biodegradable engine wiring harness issue, and the same kind of deterioration in the throttle body wiring as being things to look at. I haven’t taken the car to a workshop yet, as I’d read that if I had a degrading wire harness then this can also show many phantom fault codes.

Does anyone have a suggestion as to where I start looking first? Additionally:
- Are early W210 E-class (pre 1997) also prone to these wiring bio-degradation problems in general?
- On the M111 engine, where can I find the i.d. / part nr. tag for the main engine harness? Should it be close to the engine ECU connector?

Thanks in advance.
Ross

 

[91dm]

Hi Ross,

I don't think the 210 suffers from the same harness problem. I have a early 96 E200 and harness is still ok.

Did you change the plugs as well as the coil and lead?

 

[TourmalineE230]

Hi Ross,

I don't think the 210 suffers from the same harness problem. I have a early 96 E200 and harness is still ok.

Did you change the plugs as well as the coil and lead?

Thanks, I need to check my harness more thoroughly.

I haven't changed the plugs yet, they should arrive in the next day or so. But if I have a dud spark plug, surely that would show up whether the car is revving in gear or in neutral, right?

 

[91dm]

I have seen a cracked spark plug do all sorts when under load and ok the rest of the time.

 

[carat 3.6]

An early w210 can still suffer from the failing wiring loom, although the throtle body is a more common failure point. Take a look at some of the sensor plugs around the engine, if you see bare copper or cracked insulation that will most likely be your problem.

 

[TourmalineE230]

An early w210 can still suffer from the failing wiring loom, although the throtle body is a more common failure point. Take a look at some of the sensor plugs around the engine, if you see bare copper or cracked insulation that will most likely be your problem.

Thanks, will do.

 

[TourmalineE230]

I have seen a cracked spark plug do all sorts when under load and ok the rest of the time.

Replaced all the spark plugs today (old plugs looked quite ok, normal wear), although they didn't seem to be torqued down very tightly. I also replaced the high voltage boots on the coils (had to use the old ones when I changed coils a few days ago). Unfortunately the misfire hasn't really changed at all. I think it's time to stop the 'swaptronics' and look more closely at some wiring.

When I took a quick look in the compartment containing the control units, all the wiring looked factory fresh and undisturbed. Time to start digging further.

 

[91dm]

If you type your VIN into this site you'll be able to find the wiring harness part number and routing etc.

LINK

Have you checked the fuel pressure? Does the throttle body blade all look good?

 

[TourmalineE230]

If you type your VIN into this site you'll be able to find the wiring harness part number and routing etc.

LINK

Have you checked the fuel pressure? Does the throttle body blade all look good?

Thanks for the link. I haven't checked the fuel pressure yet, will have to see if I can get hold of a gauge. Throttle body blade appears clean and undisturbed.

I will begin to check the wiring to all the engine connectors on the weekend. The air mass meter wiring is taped near the connector so I think I'll start there and go step by step.

 

[TourmalineE230]

Spent some time inspecting the wiring today. I think I've narrowed it down regarding the misfire problem. The connector for the air mass meter had some electrical tape where it joined the harness. Upon inspection it looked a bit gruesome, so it's time to get out the soldering iron. Throttle body looked relatively ok.

 

[91dm]

Was there tape between each wire/solder joint? That doesn't look great but repairable!

 

[TourmalineE230]

Was there tape between each wire/solder joint? That doesn't look great but repairable!

There was heat shrink on each wire but it was only slid over each joint and not fixed / shrunk onto the wires. Just assessing my options about what I do.

 

[carat 3.6]

Spent some time inspecting the wiring today. I think I've narrowed it down regarding the misfire problem. The connector for the air mass meter had some electrical tape where it joined the harness. Upon inspection it looked a bit gruesome, so it's time to get out the soldering iron. Throttle body looked relatively ok.

It's the throttle body wiring you need to look at, early ones had about 1ft of cable to get to the plug.

 

[TourmalineE230]

It's the throttle body wiring you need to look at, early ones had about 1ft of cable to get to the plug.

The problems have got a bit worse, the car has gone into limp home mode twice (both times after turning left and accelerating for some reason) and the misfiring is increasing. This TB doesn't have the separate 1ft cable, it connects direct to the engine harness. I wasn't 100% sure if the TB was the root cause but the symptoms do point to it.

Anyway, I'm going to talk to a few of the TB refurbishment firms here first as I have to do something to cure the problem.

 

[TourmalineE230]

Short update: got hold of a used (known working) throttle body, swapped the existing unit out, did the re-learn procedure and immediately got a better / smoother idle..... but zero difference whatsoever to the misfire problem.

I think I'm going to have to pull the harness out and send it off for testing / refurbishment. Spoke to several local firms here who seem unequivocal in their opinion that these symptoms mean that the harness is the root cause, but then again you should never ask a hairdresser if you need a haircut!