oxygen sensor

[Doyt W. Echelberger]

At 08:23 PM 6/7/2001 -0500, you wrote:

>What are the symptons of a bad oxygen sensor? Also, when you check the
>resistance on a bad one (as per the Benteley), is there usually more
>resistance or less? (Benteley indicates should get 3-15 ohms). Thanks for
>any insight.
>
>-------------------------------
>T. L. Irwin
>T104 Coordinator
>Swain East 335
>855-3573
>php.indiana.edu/~trirwin
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>.


Hello Trevor.........I don't think you have to use electrical resistance 
tests to verify a failing oxygen sensor.  And the resistance test isn't the 
best one to indicate a failing sensor anyhow. A better test would be to 
measure  the sensor's rate of fluctuation (flicker), both at idle and at 
cruising speed. It should flicker once a second at idle and about 5 times a 
second at cruise. Older sensors show lower flicker rates, and bad ones get 
stuck and don't flicker at all or very often.

As the flicker rate slows down, your car will begin to run poorly and stall 
out and lose power. It will run like the mixture was overly-rich.

I can relate the results of a bad oxygen sensor in my 87 5ktq. The air-fuel 
ratio randomly crept into the rich range, which showed up at first in 
stalling at stoplights and a loss of power while driving in town. When I 
drove the car on the turnpike it usually ran OK, then when I got to the 
toll booth it would stall and not restart for a few minutes. Had to roll it 
off to the side and wait until it was ready to go again. But the condition 
didn't happen every time I drove the car, so I couldn't reproduce it for a 
mechanic.

This condition got worse as the sensor deteriorated further and flickered 
less often. Finally, the car lost power under load to such a degree that I 
couldn't keep up with traffic and had to pull over onto the berm to avoid 
becoming a traffic hazard. It REALLY bogged down.

When it was bogging down, I found that I could get it to run better for a 
few seconds by slamming the accelerator pedal to the floor. At wide-open 
throttle it would take off and have power long enough to get me up to 30 
mph in 2d gear. Then I would push in the clutch and coast for awhile and 
then do it again. It was a jack rabbit thing, jumping along like that. Got 
me to my mechanic, who replaced the oxygen sensor, which totally fixed the 
problem.

So, why did it run better at wide-open throttle? The mixture was already 
very rich, and at WOT the engine was getting more air, which brought the 
air-fuel mixture back into the range where it could burn efficiently.

If your car is bogging down, stalling out, losing power, try putting your 
car in second gear and flooring it and see if it runs better briefly. That 
would be indicative of a failing oxygen sensor in my opinion.

Check out what scott mockry sez about oxygen sensors:
http//www.sjmautotechnik.com/ecusys2.html#o2


Doyt Echelberger