I checked a duty cycle in my 260E 1987 - 97% on idle (pin 3 and pin 2 as a ground).
I was not able to change it by a screw for adjustment airflow, only O2 reading was adjustable.
The O2 sensor reading is constantly changing from 0.2 to 0.8 V. When I push an acceleration pedal the O2 goes for a moment lean to 0.06-0.02 but then jump to 0.8. The car does not response quick enough on acceleration.
When drive on highway the reading is in same range 0.2-0.8. When I release the acceleration pedal and leave the car to run by inertia O2 reading goes to 0 V, even in minus.

As I understand a duty cycle has to be about 50% and O2 - about 0.5 V ??

__________________
1987 MB260E 187K

Yes, at 50%, but the car MUST BE AT OPERATING TEMPERATURE!

Good luck,

Andrew:

Sounds like you are going lean momentarily on throttle opening. This is, I think, a bad thorttle pot on the side of the fuel distributor. Do a search, it's been disussed in detail, especially a source for a new one instead of a $1600 fuel distributor!

O2 sensor is working, it should go to 0 on coast since the engine computer shuts the fuel off (and this also means the fuel system it working, at least partially).

I would look for a vac leak -- you are due to replace ALL the vacuum line rubber connectors, the idle control valve hoses, and possibly some AC components that have sprun leaks. All will cause throttle lag and mixture problems.

Also, try leaving the black (ground) lead free, ungrounded -- on my cheapo meter, ti get 90-100% duty cycle with the black leak grounded. If left free, with the red leak in the #3 connetor, it works fine. Go figure!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Wow I didnt know that. You tend to completely trust the numbers these meters give you. I get a 96.7% duty cycle. I will check this.

Is your car a CA model? Even if not I sometimes wonder if people are checking the duty cycle properly.

www.landiss.com/mixture.htm

has a very good write-up on how to check if your car is 49-state or CA and then set the system to "test mode" if necessary and procede with checking duty cycle.

Anyone interested in checking duty cycle should print these web pages out, read, and thoroughly understand how to do this procedure. Otherwise you may get false readings.

Duke

I would get a solid ground not that pin 2 one! I have always taken it to a real true ground on the Body. I never trust ground wires....

__________________
~Jamie
_________________
2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....

Thanks everyone.
I tested a duty cycle with ground in the pin 2 and from a carv body and I also noticed that it works without ground at all. The numder is the same 97% on the warmed to 80C engine.
My AC is broken but I could not think that it could be a problem for car performance. Thanks.

__________________
1987 MB260E 187K

With the ignition on but the engine not running, the duty cycle tells which version of controller is installed.
A 70% duty cycle indicates the standard controller with the ability to read some faults by monitoring the duty cycle.
85% indicates the California controller, which ordinarily displays the faults as a blinking LED on connector X92, although it can be programmed to display the faults as an X11-pin3 duty cycle.
100% indicates the controller does not display fault codes in this manner, or is faulty.

Main shows constant 97% in the static test.
It drops to 10% when RPM about 2000-2500.
Is it bad controller? The car runs pretty good on 60-90 mph.

__________________
1987 MB260E 187K