It sounds like possibly an OX sensor wiring issue. After starting the
engine the ECU always IGNORES the signal from the OX sensor until the
reading the ECU sees from the TempII sensor tells the ECU that the
engine is getting warmed up. Then the ECU uses the signal it sees from
the OX sensor as the basis for adjustments the ECU makes to the fuel
mixture. Having already  changed the OX sensor proves nothing  Even
unplugging the sensor proves nothing. If there is a problem in the
wiring between the ECU and the OX sensor the ECU can screw up the
mixture as soon as it sees a warm engine, whether the OX sensor itself
is good or not.

There are 3 common ways the wiring to the OX sensor gets messed up.
Usually it has to do with someone installing a generic OX sensor and
screwing up the splicing of the wires. Another possibility is the ground
wire for the OX sensor. This ground wire is not in the same harness as
the other OX wires. It is the lone brown wire in the small bundle that
goes to the distributor connector but split off to a ring connector that
is then screwed down to metal on the engine. Check that this ground wire
is making a good contact to the engine.

There are a few simple tests that should be done to the wiring related
to the OX sensor to verify that it is all correct. Maybe tomorrow I can
post details of those tests.

Mark

JordanVw@AOL.COM wrote:

>a friend of mine with a '87 westy weekender is having problems with his
>van...  he wrote:
>
>"chris ..here is what is going on
>we have replaced the spark plugs,wires,cap,fuel regulator valve,fuel
>injectors,o2 sensor,gas tank,fuel filter,and we are running out of options...
>the vanagon runs good until it heats up and then runs rich producing black
>smoke as well as stalling out and shaking really bad ...please help   thanks
>jeff"
>
>can anyone give an idea as to whats happening here?  and ideas would be
>appreciated..
>i told him it might be a ECU issue but he wants the combined wisdom of the
>list first..
>
>
>thanks
>chris
>
>
>