[Diy_efi] O2 Sensor or Computer

[Shannen Durphey]

Some suggestions:

Try reading the O2 voltage between the O2 wire and collector when this is
happening.  Does it agree with the readings at the ecm?
Check that voltage at the ecm power supply lines isn't dropping below 9
volts during hot crank. It might be best to connect meter leads across both
the ecm power and ground terminals.
Is car a manual trans?  If so, will pop starting it make the problem
dissappear?
Check that the O2 sensor circuit low line from the ecm has a good
connection at the block and that it isn't conducting excessive current
during a hot crank.
Try the Ferd diagnosis trick:  "Replace with known good part."  Delco parts
tend to have the best success rate, IME.

How warm is the area where the ecm is mounted?  Does it get warmer when
sitting (say during a fuel stop?)  Does removing the cover or cooling the
ecm help?

Some schematics may be available at Ludis' site.  I think the 7747 is
there.

Sounds like a pistachio ice cream driveability problem to me.
Shannen

Peter Foote wrote:
> 
> Hello;
> 
> Here's a strange one I've been fighting for a while but it showed up
> perfectly tonight. I was driving my car with a throttle body '747
> conversion. The O2 sensor was giving a good signal and the computer was
> self-learning. The integrator values had mostly returned to 128 and the
> block learn values were mostly above 128. It was running really well.
> Perfect, I thought.
> 
> Then I stopped for gas! After that, the block learn values all began to drop
> to 125, which is the min. value I allowed. The O2 sensor was constantly
> reading high and causing the computer to "de-tune" the motor so lean it
> wouldn't run right. It's done this cycle a few times and really has me
> puzzled.
> 
> I have a 1-wire O2 at the collector in the exaust but it does read right
> some of the time so I don't think it needs to be heated. It's behind ceramic
> coated headers and they seem to really hold the heat in. Also, I had a meter
> connected to the O2 sensor and it was reading the same high numbers the
> computer was. This makes me think it's the O2 sensor. Anyone ever see an O2
> sensor ntermittently work?
> 
> Can the computer back drive the O2 sensor? Anyone have any partial
> schematics of the O2 input section for that computer? I probably have to buy
> parts either way and would like to replace the right one.
> 
> Peter
>

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