82 380SL oxygen sensor/lambda question - PeachParts Mercedes-Benz Forum

PANZER · #1 08-14-2010, 12:15 PM

I have researched all of the O2 threads and posts and they come close to answering my question but not fully.
The car runs rich from day 1. Did a voltage check on O2 and it read 0.23 indicating lean. The meter did not fluctuate but just locked on that reading. Replaced sensor w Bosch unit. Drove it to mechanics shop independent certified MB and it read 0.34 locked. I unplugged the unit and tested the sensor and it started climbing. Plugged it back in, locked at 0.34.(it came up to 0.35 when I shot a mist of ether into the throttle platen, I though it would jump up more than that!) Pulled unit and burned off the black carbon that built up over just 30 miles of driving (gets about 6mpg at this point, I worry about choking my catalytic converter.) Replaced and checked again,0.34, no change in voltage. I am thinking of the green wire being shorted somewhere, or jetronic failure

Last night I pulled the plug and cleaned the contacts on jetronic (will check later, raining now) is there anyway of disassembling the jetronic and resoldering? I read about a coolant sensor coming into play, local parts house does not carry it and Iam not sure of its exact location on my car. I love driving this car but traveling with a gas tanker truck is cramping my style!

mbdoc · #2 08-17-2010, 09:38 AM

Lamda (O2 control closed loop) is designed to only control the mixture when you are fully warmed-up and the BASIC fuel mixture allows that to happen.

The basic fuel mixture is dependant on fuel pressure! System pressure vs control pressure.

PANZER · #3 08-19-2010, 12:50 AM

I drove the car 16 miles to MB mechanics shop so it was warmed up to about 90. The first thing he did was to check the fuel pressure to warm up regulator and that was fine, I don't rememeber the actual numbers at this point, but he said the pressure was fine, we even cleaned out the screen on wur. HOWEVER, i MAY have done something to throw myself under the bus...
I have a small exhaust leak , a slit at the Y joint on pass. side. Welded up crack all but a 3/4 inch spot where mig head would not pass around the pipe. I will get hubby to get torch and finish the weld. Anyway, I replaced the O2 sensor and replaced BOTH conectors as the one on the green wire coming from Jetronic, came off in my hand! I did not know at the time that this was a shielded wire, so I cut off the frayed stuff and CRIMPED a new connector on the whole thing. Now the new O2 sensor acts like it is shorted out as it locks at 0.34 and does not fluctuate. It does so if I unplug it though. I pulled and cleaned contacts on Jetronic with no effect. I will be checking my connecter work in the green wire to see if I have done this to myself and hope I did not mess up the jetronic.

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david s poole · #4 08-19-2010, 02:29 PM

you shot yourself in foot the "frayed wire" is a ground shield and needs a separate connector from signal wire.