O2 sensor

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Chicobiker - 18 Apr 2009 03:21 GMT

One more post while I'm on a roll ...

2003 OBS, 190000kms.

My check engine light has been on about a year now. I checked it out
then, it was front o2 sensor. Car was working fine, same gas mileage
as day 1, so I let it go. No change in performance since then.

I figure if the front sensor is gone, replacing it will result in a
message that the rear one is also gone. Replacing both will probably
lead to a message that the cat is gone. I'm afraid of a domino effect
so I left it alone.

I recently had to replace a section of that exhaust pipe (cracked at
the brace), and the mech told me that if the o2 sensor isn't working,
the engine could be running rich and that could ruin the Cat.

So, my question is: What symptoms would I have if the car was running
rich?

Thanks.

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S - 18 Apr 2009 23:55 GMT

Hi Chicobiker!

>So, my question is: What symptoms would I have if the car was running
>rich?

Loss of fuel economy is the most easily observed symptom. If you have
been getting around, say, 27 -28MPG, and this drops off to 24 or
25MPG, that would be about typical. Black sparkplug electrodes, black,
sometimes black and wet-looking deposits at the tail pipe, and in
extreme cases, a smell of gasoline in the exhaust, are as well. Unless
things are to the "gas-smell-in-the-exhaust" point, you are unlikely
to notice much loss of performance, tho.

And your wrench is quite correct; a bad front O2 sensor will cause the
engine to run in "limp" mode, which is deliberately rich to avoid
possible damage. Operating the vehicle in this mode for very long will
decidedly ruin your catalytic converter. If you've been running in
limp mode for a year, tho, it's already toast, and you probably have a
whole string of OBDII codes regarding the O2 sensors, and catalyst
efficiency.

At this point, your best bet will to see if you can find a Y pipe (??
. . . Whatever components hold the CAT and O2 sensors on the '03 car.
I _think_ they're all in the Y pipe. Anyone?) at a salvage yard.
Technically, I don't think they are supposed to sell used emissions
control components, but probably if you ask nicely, AND ask for an
"exhaust Y pipe" rather than "the catalytic converter", you'll be
able to land one. Swap in the whole shebang and be sure to reset the
ECU before driving far.

Hope this is helpful.

ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

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