Edited with a better summary of what's wrong, and more tests i've done. Any CIS experts please chime in!


I'm pretty stumped with this problem i'm having with my 1992 N/A 2.6 190e. In the battle of trying to figure out why i can't pass emissions, i found something quite weird with my car while looking at the mixture at the X11 Diagnostic port.


According to BOSCH KE3-JETRONIC MIXTURE ADJUSTMENT, the static duty cycle should be 70%, with ignition on engine off. which means the voltage between pin 2 and 3 on the X11 connector should average around 4v.


1) Yet I'm averaging around 8v, which is around 33% duty cycle? What could be causing this?


If I open up the throttle, the reading would increase to 10.5, and drop back down to 9.33 at WOT. This is mostly normal.


2) However when i deflect the air flow plate with ignition on, engine off, the duty cycle does not change at all. What could be causing this?

- The airflow meter tests fine, with smooth rise of voltage to 5v, all within spec.
- The connection between the AFM and the ECU is also good
- The throttle valve switch is also good, both at idle and full contact
- The connection between the throttle valve switch and ECU is also good


Other symptoms:

When I open up the throttle, i'm suppose to see momentary enrichment, the duty cycle should temporarily drop (voltage goes up), however it actually does the opposite, and leans out.

With the engine warm and idling, my duty cycle is around 8v or 30% (rich). However when i rev the engine to 2500rpm, it drops down to 50%.

If i adjust the duty cycle to 50%, or 6.8v at idling, when i rev up the engine to 2500, the duty cycle will lean out to 60%. And if i rev it hard, the duty cycle will lean out to over 90% briefly!

My emissions report also reflect this. I failed on NOx (lean/hot combustion), and you can see it spike everytime the car accelerates.

Any help is appreciated! Sorry for the long post.