More on 220E fuelling

[tradedog]

A follow on to my query on my 220E running rich and surging at idle. I did the throttle body and butterfly clean up as suggested. It was fairly dirty, mostly black oily buildup, came off easily with a rag soaked in methylated spirit.

I then reassembled and ran the motor. The surging had gone but the idle is still lumpy and erratic.

I have a few queries that I hope the boffins (220E or C220) out here might be able to help me with.

(1) Is the air flow/air mass meter the cylindrical device just downstream from the air filter, or is it the small “probe” type device which is in the air ducting in the curve just before the throttle body? Whichever it is, what is the other one?

(2) I have seen suggestions to clean the air mass meter by dipping the “hot wire” into alcohol. Should it be “wiped “ in any way? Should I clean both the devices mentioned in (1) above in this way?

(2) I have see MB mechanics “twiddling” a brass screw which is found attached to the rear of the false bulkhead on the drivers side when “tuning” these injected motors. It is a fairly large screw head recessed in a black tube which is above and to the right of the brake fluid reservoir when viewed from the front. Does anyone know what this screw does?

(3) Is it possible my problems stem from the cold start device on this motor which is not switching off? Ie. Is the motor getting extra fuel even when its hot? How could I check this?

My thanks in advance.


PS: How do I change my profile to get alerted of responses by e mail?

 

[C220GJS]

Hi, hope i can help with some of your questions.
(1) The black cylindrical device after the air filter is the air mass meter, the other probe is the inlet air temperature sensor.
(2) I would suggest cleaning the AMM probe with an IPA spray as if yourAMM is like mine you would have to drill out screws to remove the probe,in any event do not touch either of the probe elements as they are very fragile.
(2b) Can't help re. the brass screw,will need to have a look for it next time i have the bonnet up. Will let you know if i find out.
(3) Suggest your overfuelling problem may be a faulty oxygen sensor (lambda).Do a search on the forum.Then probably best to have fault codes read as; if it is overfuelling it will destroy your catalytic converter in a very short time.
Obviously from what i have said ,the important thing is the overfuelling and should be dealt with asap ,having the codes read should show up any other existing problems, use an independant unless you have money to burn.
Cheers Geo.

 

[Silver Arrow]

Gungy fuel and air devices tend to respond to a good squirt of carb cleaner.

Too much could, I suppose, upset other bits down the line and produce flames out the back end!

Ah! you could fiddle with carbs and really screw up things!

 

[mjtray]

does sound as if your Lambda probe has given up the ghost....they should, in a way be a service item that needs replacing at a set time/mileage.

I've had one fail on a E280 and my fuel consumption increased big time and the car appeared to be over fuelling.

 

[television]

Just for reference the Lambada should be replaced at the same time as the cat, one of its purposes is to protect it.


Malcolm