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Top diagnostic tip from Autologic

Autologic’s Mercedes-Benz Technical Support team shares its knowledge on a common fault for 112 and 113 v6 and v8 petrol engines.

The Complaint

Holding back / flat spots / possible bad starting / uneven idle / misfiring / juddering / high fuel consumption / gearbox flare / uneven gear changes etc.

Typically, symptoms show themselves through a very slow performance deterioration so that normally it is only after the vehicle becomes barely drivable, that a good many customers seek garage help!

Using a diagnostic tool such as the Autologic, a technician may find a number of fault descriptions present. It is worth noting that that there are various code numbers for different variants. Common fault descriptions are:

Self adaptation of mixture formation ME-SFI control module(n3/10), part load for right bank of cylinders at limit value (current & stored).
Self adaptation of mixture formation ME-SFI control module(n3/10), part load for left bank of cylinders at limit value (current & stored).
G3/3 right o2 sensor before TWC (not defined ). (Stored)
G3/3 left o2 sensor before TWC (not defined). (Stored)
Misfiring damages TWC and misfiring cylinder (could be 1-6.) (Stored)

If an air mass problem is suspected, the air mass meter could be disconnected (electrically) and then if the vehicle is driven, more power should be exhibited. Usually, if the ignition is re-cycled, the vehicle will drive better for a while but you will obviously have a fault code for air mass logged in the engine ECU, which will subsequently need deleting after air mass replacement.

Note: Air mass actual value is often out of specification but not always as it is only tested for reference value on idle speed. After replacing the air mass the adaptations must be reset.
On the Autologic, select Adaptions in ‘Control unit adaptations’.

Then go to first initialisation and perform Adaption Reset and Clear Codes.However be aware that this process will set the ignition and injection adaptations back to factory settings!

With an engine that has covered in excess of 60,000 miles and has worn plugs and/or part-worn cylinder compressions and injectors/throttle flaps etc., it will probably run rough and not even idle at all and, in fact, can seem worse than before. If this is a possibility, cleaning the throttle valve venturi in an area where the butterfly shuts, helps to clear a build up of carbon deposits. This should then be followed by a default initialisation procedure.

Note: If the engine does have a high mileage, simply try to fit air mass and let it adapt over time. A tip for a successful default initialisation process is to check the fault memory in traction control after default initialisation and, if any codes are present (can communication with engine), it has not been successful. When this occurs, the throttle body flap should be re-cleaned and default initialisation should be tried again until no faults are present in traction and the vehicle idles okay.

Autolocic is represented in Ireland by Diagnostic Solutions. For more information on the Autologic range of diagnostic solutions phone Diagnostic Solutions on 01