What would cause an open loop fuel system?

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Active Member
Mar 1, 2010
Hi. For my W208 CLK230K, I've been have an excessive fuel consumption problem for quite a while now. 60L would run me perhaps 380-400km , This is in excess of 15l/100km !
Compression test shows everything OK. Star Diag shows no fault codes.
As a last resort I bought the AutoTap software and OBD II reader.
What that showed was that my car is in perpetual open loop in the fuel system.
O2 sensor tests could not complete for some reason.

I went out and changed my temp sensor, fuel regulator and the 2 O2 sensors as a result. Still no change. Can anyone here suggest a reason ? Faulty ECU do you think ?
Check the actual operation of the O2 sensors with a meter, there may be a lack of supplying power.
Thanks for the reply.
What would cause a lack of supplying power though?

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