Bad o2 sensor symptoms?

[YungICY]

What are the symptoms of a bad o2 sensor? My afr guage is all over the place, the motor bogs down really bad in lower rpms then will jump to life like a 2 stroke once it gets up higher. I just put an 88 2.3 into my 85 2.3 truck. I'm running the 85 eec, it seems to be performing much better than the 88 eec although both are displaying similar symptoms.





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[adsm08]

Could be an O2 sensor. Does it run fine for a few minutes when cold then start acting up and remain consistently crappy once warm? Does it help to cycle the key quickly?

A bad O2 ground can make the same thing happen. If a 3-wire O2 sensor isn't grounded to the block the computer can't see the signal.

 

[RonD]

Generally an O2 sensor will slow down in response time and start reporting too much oxygen(lean) so computer runs engine richer than it should.
Lower MPG is often a sign of failing O2 sensor

One thing to remember is that the O2 sensor(or sensors) are not used by the computer until engine warms up, O2 sensors can not work until they are above 650degF.
So if symptoms happen only when engine is warm it could be a failing O2 sensor, but if it happens cold or warm then it wouldn't be O2 sensor.

O2 sensor life is estimated at 100,000 miles, my 4.0l has 300k+ and still using original O2s

A vacuum leak effects lower RPM more than higher RPM
Could be one dirty injector causing the AFR up and down

 

[YungICY]

Thanks for the info guys. It could possibly be one of the injectors. I will make sure its only happening when warm. It could possibly be a vacuum leak but I'm pretty sure its not.


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[ab_slack]

A easy diagnostic, unplug the sensor...That will be seen as bad and ignored. Does it run better?

 

[YungICY]

You're never gonna guess what it was. First a swapped the sensor with the one I knew was good from my other manifold, same problem. Then I decided to go with process of elimination. Thanks to Ron I decided to double check for vacuum leaks. No leaks, but I had plugged the evap line from the gas tank into the brake booster hose since my truck has manual brakes and I plugged its actual vacuum port which is just before the throttle plate. I switched those and violá.



Thanks again everybody for the good advice and direction.


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