Mercedes-Benz W126 runs too rich: causes and lambda sensor check
W126 runs too rich and the spark plugs get wet, what could be the cause?
On KE-Jetronic injection the cause can be a leaking cold start injector that lets fuel through continuously. A break in the temperature sensor wire also makes the car run rich when warm. A stuck fuel distributor can feed too much fuel already at start-up.
What should the lambda sensor voltage show?
The voltage of a warmed-up sensor varies constantly between about 0.4 and 0.9 V when the system is working. Measure the green signal wire against chassis ground with the engine running. A reading that stays constant points to a fault.
What happens if the control unit does not get power?
If the control unit relay is broken, the car goes into an emergency running program and the mixture is slightly rich across the whole operating range. The lambda sensor then does not regulate the mixture, but the fuel pump circuit is separate and the pump works.