At 04:01 PM 6/27/98 -0500, John H. Rodgers wrote:
>-- [ From: John H. Rodgers * EMC.Ver #2.5.02 ] --
>
>Michael, I just did the same thing. Installed new O2 sensor, now engine
>tries to stall when starting off unless I really put the pedal to the metal.
>Seems to have a dead spot since installing the new sensor. Aggravating,
>could get me run over at a stop sign or red light when trying to get away
>with reasonable nimbleness. Not sure what to do at this point. Do know my
>mileage was down and tailpipe black. Figured this would help out, but acts
>very much like the old carbureted engines when the accelerator pump on the
>carburetor wasn't working properly. Would try to stall out. The slug of air
>going in leaned the mixture momentarily before the accelerator pump could
>enrichen the mixture, so the engine would nearly stall. Same type of thing
>is happening with my fuel injection now that I have a new O2 sensor. Engine
>tries to stall on initial acceleration.
>
>Comments would be appreciated.
>
After I changed my O2 sensor, the van would start and run a few seconds and
then die. Turns out I knocked the vacuum line for the brake booster off the
manifold. Took me a while to figure this one out. Take a good look around
the engine compartment to see if anything is obviously amiss. Did you do
anything else while changing the O2 sensor? If so, double check that
work--might not be the O2 sensor after all.

Otherwise, you just have to start going through the standard FI checks. If
the van runs fine with the O2 sensor disconnected (before starting the
engine), then the problem is most likely related to the O2 sensor. Check the
output of the sensor while it's disconnected (again, disconnect before
starting the engine). You should see a steady output between 0V and 1V as
the ECU is operating in open-loop mode and won't be constantly adjusting the
mixture. Anything else and you have a bad sensor or a wiring problem. If
this test checks out OK, then stop the engine, reconnect the sensor, start
the engine and again observe the output of the O2 sensor. It should remain
fairly steady until the engine warms up and then it will start fluctuating.

It's quite possible that the O2 sensor if just fine and something else just
happened to fail at the time you were replacing it. Murphy's Law you know...

-Mark McCulley