1990 300CE eating my lunch

[mbtech161]

Customer's vehicle has been to 2 other shops w/ no fix.Now it is my problem.Started off w/ fixed 10% lambda.Tested using factory harness and found 3.9 mv at O2 sensor signal line.w/key on and running.Found this after chasing tail,new air flow meter,etc...-Found used ECU and installed.Lambda online ,50% at warm-up,then would slowly drift to 10%. monitoring O2 and at EHA ,could lean mixture to about 730mv and watched EHA react-EHA would then go to a full lean state.No control in midrange.New and old O2 sensors react the same.No DTC's from CIS-E,EZL,orMAS.Appeared head had been off.Checked base cam timing,intake cam was off 1 tooth.Fixed cam timing.Reasssemble and rechecked.Still unable to get lambda to sweep.Either full rich or lean.Ran a compression test and all cylinders are at 210-220 psi.Seems too high for a gas car???Pulled the head,thinking maybe head had been milled/decked.Does not look like it has.Im baffled.
Anyone run across this before?