Lambda results questions
 

I recently checked the lambda value on my '91 190E 2.3, looking for answers to a rough start and sluggish acceleration. I was using a Fluke 87 to measure the duty cycle and the results are confusing me. Rather than the 45 - 50% I was expecting, the duty cycle varied a great deal. values would bounce from 0 to 100, then drop quickly through the range, with values in the 80's. 50's, 20's etc. Then the cycle would repeat with lots of variation. I had a good chassis ground and a good connection to #3 pin on the diagnostic plug. The engine was also warm, at 80C. The car doesn't really run bad, just a bit rough on idle and a bit weak on the acceleration. The engine has 148K on it. Any suggestions as to where to check next. I haven't checked the EHA current yet, but will look at it this weekend to see what the controller is actually doing. Any thoughts you may have would be appreciated.
Thanks,
Ted

To verify meter function try the measurement Key On Engine Off. You should get a fixed duty-cycle of 70% if its a Federal car and 85% if its a Ca car. It should not vary.

If you get one these values steady then we need to figure what your results mean.

How is the output signal from the O2 sensor? Is it as wildly erratic as the duty cycle??

Intruder

Steve,
Thanks for responding. I checked the ratio key on, engine off as you suggested, and got a steady 85%. This was what you said a california car would display. I was surprised to find that this is a '91 california car, as it was purchased new in Oklahoma in '91. I purchased it used in '99. To further confirm this I was reading in the CD manual and found that for '88 to '91 california cars, they provided an on-board diagnosis system with a switch and LED at the X92 connector to show and clear DTC's. Further, it says that you have to use the DTC switch to change between on/off ratio output or DTC output. I haven't been able to check it yet, but am sure that it wasn't outputing ratio data to pin 3. I'll check it after work and post the ratio results.

By the way, I'm still a little suspicious that this is really a california car (even though all the evidence says it is). How can I verify this? The VIN is WDBDA28DGMF827214. Can I tell from here.
Ted

Intruder,
I haven't checked the O2 sensor yet. Once I get the ratio figured out, I'll check that. Thanks for taking time to respond.

It must be a Ca car. To verify, check your emissions decal on the radiator core support. If its yellow its a Ca car. It will also state on the sticker the same.

If it is a Ca car you will have to turn on the off-on ratio output. This only requires pushing the trigger button for a couple seconds.

Yes, it's a California car with the yellow emmisions decal. I was able to verify the on/off ratio now, and it is pretty steady, with a low of 52% to a high of 58.5%, with the average at 56.5%. Within specifications, but maybe a little lean. Would you change it if it were yours? Seems in other replies that you recommend around 45%.

Thanks again.

Yes, I usually set it up a little richer, as noted. When warm and in steady state it won't matter where you set it, but cold or when accelerating the mixture is due to the base setting as the electronics are either asleep (till the O2 sensor warms) or too slow to keep up (as in sudden acceleration).