Scissors from my WIS 2006:
"The heating element of the oxygen sensor is supplied
with voltage via terminal 87 of the fuel pump relay and
is heated for as long as the fuel pumps is running."

Can this be healthy for the Oxy sensor? I have recently changed the Oxy sensor on my '87 230TE, for the second time due to performance failure when the engines temp's coming above approx +40°C (+104°F?). Last time this occured it helped with a new Oxy, or just to pull out the signal cable so the KE running Open-loop-management.

But what's really confusing is that my other Merc, A 230CE '88 with same setup for the Oxy-preheating, is running properly (is that right spelled?) and no burnt' Oxys...

The small "spark catchers" is empty (not on the Coupe), and so are the catalyst too on both cars.

Could it be those empty "spark catchers" that messes around with the oxy?

Worth to mention: For a month a go, I welded pipes thru the catchers to get rid of the "empty cat noice" so we'll se what that will do!?

__________________
Patrik Nilsson -83
230CE -88
230TE -87
http://www.hastonnet.se/putte/avatar-new.jpg

The O2 sensor's pre-heat voltage is pulse width modulated by the ECM in order to prevent overheating it.

According to the electric schematic it's preheated directly over the fuel pump relay, w.o.w the same pin that's feeding the fuel pumps with power.

The negative is directly to ground.

__________________
Patrik Nilsson -83
230CE -88
230TE -87
http://www.hastonnet.se/putte/avatar-new.jpg