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Old 05-09-2001, 07:09 PM
Posts: n/a
I read Steve's article about monitoring the EHA current signal.

I had to do the same thing when I bought my 190E 2.6. It got 19MPG and the plugs were black and black smoke on idle.

I monitored the oxygen sensor and EHA and after awhile saw the relation and pin poined the oxygen sensor...the voltage was going down to -20 mV and the EHA current to 12 mA or so. Rich rich rich.

With a new o2 sensor I'm now up to 28MPG /31 hwy, plugs are white/tan. Its a little harder to start cold,5-10-15 sec crank time. 1 -2 sec when hot.

My question concerns the EHA values he reported as GOOD values. Mine are a little off: Here they are:

Cold start 40F goes to 24 mA and as I drive works down to
-2 to -4 mA and stays around there as I drive around town or hwy.

Hot idle goes to -9 to -9.8 mA and then stays at -9.8 mA.

Hot full throttle goes to +4.5 mA and stays.

Coasting down goes to -64 mA.

I think maybe I'm a little on the rich side.

When I put the new o2 sensor in I adjusted the throttle plate to "zero position" (I think is what the Mercedes manual called it) and as I tested and watched the signals I leaned it out 1 or 2 turns until the the hot normal driving was at -2 or so mA. I didn't know where to set it and made the guess for a little rich throttle plate adjustment, and of course now having seen Steve's data...

What do you think ? Should I lean it out another small amount or so ?

I have a scope but cannot drive around with it as it takes 120VAC.

I remember the manual says that you can reach a point(too lean) where it may not start. And as it seems to start a little hard now ????? I'm not sure...

Oh yea when the sensor was bad it started in just a 1-2 sec. crank.

When I say hot I mean normal operating temperature.

Car specs: 1989 190E 2.6, 5 spd manual, 147,000miles, oil might go down 1/2 quart for 3000 miles.

I know this is long and windy but please respond.

Bill Bass
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