Mark;

This is what I'm trying to avoid. I really want to make sure that it
isn't the O2 sensor. But when I take out the O2 sensor, it runs fine.
When I take out the Temp II but not the O2 it runs badly.

On Thu, Sep 11, 2008 at 3:28 PM, mdrillock <mdrillock@cox.net> wrote:
> It seems like we go around and around on this several times each year. Just
> because the engine seems to run better with the O2 sensor unplugged IN NO
> WAY demonstrates that there is any problem whatsoever with the O2 sensor
> itself. Most likely the problem is something else and all you have done is
> mask the problem. Yes, it could be the O2 sensor is bad but that is far from
> certain at this point.
>
> One real possibility is you have lost the ground for the O2 sensor signal.
> It is a small brown wire in the bundle that goes to the distributor. The
> other wires in that bundle are for the hall unit but the brown wire is just
> for the O2 logic in the ECU and not for anything else. The brown wire
> normally has a ring connector on the end and it needs a good clean
> connection to bare metal on the engine. It should never share a bolt/screw
> with any other ground wire.

I took special care when I rebuilt the engine that this ring connector
is well grounded under a nut on the stud atop the intake plenum. It
shares with no other wire.
>
> Other things, like a bad injector, can cause this same kind of symptom. The
> ECU uses the reading from the O2 sensor to know whether to lean or richen
> the mixture. If one cylinder has a problem that screws up the exhaust gases,
> the ECU will try to get the average reading closer to normal by adjusting
> the mixture of ALL cylinders. If one injector is too rich the ECU can't tell
> it is just one. It will turn them ALL down. It will keep turning them down
> more in a futile effort to get the average reading fixed. If it does this
> far enough the engine will run like crap or stop running. With the O2 sensor
> unplugged the ECU can't see the grossly off mixture from the one bad
> injector so it will just use a default setting for all injectors. This is
> just one example of why disconnecting a good O2 sensor can give the illusion
> of improving things.

Well, for a few bucks, one of the listmembers is going to sell me a
tested O2 sensor and for that kind of money I will know for sure. Plus
it doesn't hurt to have a spare O2 around even if mine is working.

I started the car and let it get hot. I put my digital multimeter on 2
volts and checked the terminals. It read 0.00.

Jim
>
> Mark
>
>
> Jim Felder wrote:
>>
>> And the loser is.... the oxygen sensor and the winners are those who
>> suggested that I remove it from the loop.
>>
>> I just went for a five minute test drive and the van drove great.
>>
>> Now, what's the downside of running without an O2 sensor? There must
>> be one. Mileage?
>>
>> I think I even have a good one somewhere. I usually replace them every
>> couple of years but I never knew why. I do now! The last one I took
>> out is probably good and I think I saved it. In the time it takes to
>> find one or buy a new one, I wanted to know if there is a danger in
>> driving with it disconnected.
>>
>> Jim
>>
>> On Thu, Sep 11, 2008 at 1:46 PM, Jim Felder <jim.felder@gmail.com> wrote:
>>
>>>
>>> OK, here's the news: I just went out and tried it again and it
>>> stumbled to a stall in about a minute.
>>>
>>> Then I disconnected the O2 sensor. It ran strongly for five minutes or
>>> so, longer than at any other time today. Then while it was running, I
>>> plugged it back in and it was dead in 30 seconds.
>>>
>>> I will try to repeat this again in a few minutes to confirm what I
>>> think just happened.
>>>
>>> Jim
>>>
>>>
>>
>>
>>
>
>
>