Steve,

I have read your article regarding the evaluation of electronic engine controls. It is very informative.

I have a 1992 400e (Federal). After reading your article, I wanted to see how my car was doing in regards to the duty cycle.

Keep in mind that my car is running fine. No problems what so ever. Just passed the NC annual inspections. Runs VERY strong, no idle or starting problems at all.

I connected an oscilloscope to the signal wire of my O2 sensor. I did not disconnect it, but just tapped into the signal wire. With the scope set to .5 volt/div, I could see the signal hovering right around .5 v. When I blipped the throttle, I saw that the signal rose to .9v and then settled down to .5v again. So it appears that the O2 sensor is working fine.

I then moved to the X11 connector, pin#3. With my multimeter set to a DC duty-cycle, I connected the neg to a ground and the pos to pin #3.

I got a 50% reading. It did not vary one bit. When I switch the multimeter to scope mode, I could see the square waves at around 6.3 volts move across.

From your article, you mentioned that a "fixed whole number duty cycle" indicates a fault of some type.

What could be causing the steady 50% reading on pin #3? Is there something I am overlooking or not doing correctly?

I do have a SuperChips EEPROM installed. I don't know if part of their reprogramming may be at fault. I have my old chip so if needed, I can replace that for testing.

Just wanted to know if you can point me in the right direction. This was just an adventure to apply what I read to real life. Now it has me wondering what may be wrong.

Thanks!

Just for closure, I figured it out. Duty cycly is at 46-47%.