I recently rebuilt the engine of my 88 190E 2.3 8v. I used many of the old parts that were still there outside the engine. The fuel pump and the oxygen sensor are new, but most other parts are not.

Using the Craftsman multieter switched to the option "% duty" the multimeter is supposed to show the percentage of the air/fuel mixture, fluctuating some 5% up and down. Am I using the incorrect function on the multimeter?

If I use pin #2 as ground, the reading won't fluctuate, but if I stick the ground lead to the chasis, it will fluctuate. Werd.

The readings are around 25% fluctuating a little up and down. If I alter the mixture, I see some change, but never leave the 19-31 range. Someone that has done this before may say that it's "too rich" but it rather sounds to me that it's an error code

If you feel that's an error code, what could be the possibilities ???

Thanks for any comments