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Old 05-21-2001, 12:59 AM
Posts: n/a
I've been working on an 84 380 SL off and on for about the last month. The customer complained about a running problem. After testing, I came to the conclusion that it was running lean. The Oxygen sensor tested bad. I replaced it with a borg warner sensor. It is now switching properly. The fuel pressure is @82 psi, the volume is 3\4 of a quart in 15 seconds. Pressure at the warm-up regulator when the car is hot is 55psi. The ignition system checks ok. Off Idle to @ quarter throttle acceleration is ok, anything after that the car runs progressively leaner. I've watched oxygen sensor voltage whiile driving down the road it shows almost 0 voltage at wide open throttle. The ECM had had water damage from the evaporator leaking on it. I replaced it. It cured part of the problem but not all. My question now is concerning possibly a bad controller or frequency valve. Before I changed the controller, the duty cycle at the frequency valve was 24%. The controller would not change it. I manually richened and leaned out the car, but the controller would not react. The oxygen sensor read fine. After I found the corroded controller, I was sure I had found my problem. After replacing it, the car still ran lean. I checked my duty-cycle again, it was still at 24%. The controller had good grounds, power, o2 readings, tps signals,and connections. If I manually richened the fuel mixture on the car, either with the mixture screw or b-12, the duty cycle would decrease to a low of 9%. If I manually leaned the car out by vaccuum leaks or with the mixture screw I would get a maximum duty cycle of 38%. At wide open throttle when the duty cycle was supposed to be at a madatory 60%, it would go to 28% consistantly. I hooked into the frequency valve circuit via mercedes shop manual for the duty cycle check. I've yet to see the 50% that all of my information says I should have. People have told me to adjust by using the air\mixture screw, the car dies from the vast amount of adjustment before it hits 40%. Is it possible that a bad frequency valve could be the problem? The only test I've seen says if it buzz's it's good. It buzz's, but I wondered if a short in the windings could cause the problem now or if I have a bad controller. The consistant 24% duty cycle of both controllers is throwing me off. I would greatly appreciate any advice or information. May God bless your days and give you the skills to complete your daily jobs.

Thankyou, Outkast
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