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Old 01-18-2007, 08:43 PM
M.B tech 20 years
Join Date: Jan 2007
Location: Atlanta,Ga
Posts: 2
Question 1990 300CE eating my lunch

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?

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Old 01-19-2007, 05:14 PM
fahrgewehr2's Avatar
Registered User
Join Date: Aug 2003
Location: Wilmington, NC
Posts: 1,264
Isn't 10% the DC code for a faulty airflow potentiometer?

300E: test sticks on 10% duty cycle
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E
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Old 01-20-2007, 09:50 AM
M.B tech 20 years
Join Date: Jan 2007
Location: Atlanta,Ga
Posts: 2
yes-10% is a fixed failure code.Using a lambda meter,this vehicle sweeps to a full rich after warm-up(pegged at 10% rich).We can see the mixture change w/EHA ma,and O2 mv.If reading was a fixed 10,we would not be able to be able to make lambda sweep to full lean w/ tower adjustment.Original complaint was would not pass emmisions,hard start

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