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

It sounds like you are using the correct duty cycle function of the volt meter.

Usually an error code will be a solid number, ie 20, 30, 50 ect. A solid 20% reading indicates a "wide open throttle contact has incorrect polarity or is defective" But it also states this reading only 20% when decelerating and the micro switch is activated.

Since you are seeing some fluctuation, I don't think this is your problem. Any other possible leaks in the system? Leak from the EHA or the O ring on the fuel distributor? At 19 - 31% something is causing the O2 sensor and computer to see a rich signal.

You could:

1. Keeping leaning it out and see what happens.
2. Sometime the O2 gets fouled. Why not remove it and look at it and put a torch on it to get it rosie red to burn/clean it off, or
3. Monitor its signal to see what voltage it is sending the computer.
4. Check the EHA current to see if it is in agreement with the duty cycle.

Just some thoughts.

Tiinker

If your follow the instructions at the following web page, you should get an accurate duty cycle reading.

www.landiss.com/mixture.htm

Note that CA models are different than 49 state models and must be placed into "test mode" to measure the duty cycle. Your emission label will say whether or not you have a model built for sale in CA.

Duke

Something to keep in mind, MB uses % off for the duty cycle readings. The resr of the world, including Craftsman, displays % on. Subtract your meter reading from 100% to get the MB codes. I.e. a 30% reading on your meter is really 70% in the MB error codes book.

If the reading is flutuating while the engine runs, it means that your O2 sensor is working and the fuel injection is in "closed loop" mode. That's a good thing.

ETC = Et cetera, Latin for "and other things"
ECT = ???

__________________
Norm in NJ
Next oil change at 230,000miles

If you disconnect the O2 sensor lead under the carpet passenger side, it better read 50%. It should also read 70% key on engine off in a federal version.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

If you have a CA model how do you put it into test mode?

You ground the appropriate pin in the connector on the passenger side for 2-3 seconds. Same as getting codes.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician