[AT] O/T Tow truck OBD II question

[Steve W.]

charlie hill wrote:
> I just bought an OBD II code reader that interfaces with my notebook 
> computer.  It's pretty impressive and gives all sorts of charts and graphs 
> of engine sensor operation.
> I'm happy with it..... almost.  The problem is that I don't know how to 
> interpret all of the data.  For example the graph generated by one of my O2 
> sensors seems very erratic by comparison to the one down stream behind the 
> converter but I don't know how it should look.
> 
> Does anyone know of a book that explains the parameters of the different 
> engine sensors and maybe has pictures of the ocillascope (sp) graphs?  I 
> finally got tired of paying inept mechanics to throw parts at a problem. 
> I'm intending to teach myself how to diagnose this stuff to the extent that 
> it can be done.
> 
> Charlie 
> 
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> 
You just discovered the problem with the PC based units. Way to much 
data with no explanations. They are GREAT for watching the data stream 
though.

Anyway. The upstream O2 is actually measuring the exhaust stream and 
it's signal is the one controlling the mix through the ECM, as such it 
will bounce around a LOT.
  The one after the cat is basically there just to monitor the output 
from the cat. It will stay in a close range as long as the cat is doing 
it's job.

Drop me a note off the list and I can give you some numbers and probably 
interpret the data a bit. Plus a few links that might help you out.

-- 
Steve Williams
Firefighter,EMT, Fire Police
VanHornesville Vol. Fire Dept