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Old 08-27-2003, 06:06 PM
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Join Date: Apr 2002
Location: westchester, ny
Posts: 747
Duty cycle 90.5% means ??????

On my 87 300e, I got a duty cycle reading with key on , engine off, of 90.5%, no fluctuations. Is this the same as a dead O2 sensor, or does it mean something else. I have a new sensor & could test it easily but only at the front pass seat-- I myself can't get under the car (the PO lowered it 2 inches). Thanks, esp to Stevebr if you can help me out.

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Old 08-27-2003, 06:54 PM
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Join Date: Jan 2003
Location: SC
Posts: 148
on/off reading of 90.5% or actually 90% means:
Electrohydraulic actuator current is implausible. A 90% duty with a running engine means the same thing. You are supposed to get 70% as it is a Fed car. Check the current with engine off/ignition on; you should see -20 mA. If you don't see that, check your OVP relay behind the battery.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer
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Old 08-28-2003, 01:32 PM
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Join Date: Apr 2002
Location: westchester, ny
Posts: 747
Thanks for your advice. I tested voltage & got -386.9mV, & got zero (0) reading for mA. Then I checked my printouts from the Forum & , to test the OVP, put the red in pin 3 & black in ground. The DMM read 1.7, which probably means the OVP is dead because that is the same reading I got from my 1991 300e from which I had pulled the OVP. Unfortunately, I can't swap the OVP because the newer one has 7 pins (& 2 fuses) & the old one has only 6 pins ( & 1 fuse). Although the fuse was changed by the PO 1 yr ago right before I got the car because the ABS light was on, I'll change the fuse & see if the reading changes; otherwise time to buy the OVP.

Last edited by richard28; 08-28-2003 at 05:00 PM.
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