i have the po154 code which is low o2 sensor effic. so i use the scanner at work and one is reading like 800 and the other is reading like 425 at idle so i replace them both. they both read around 800 but now i have a missfire on cylinder 7 and only that cylinder. how the hell does an o2 sensor cause a missfire on only 1 cylinder. so i swapped back and the missfire is gone but now im back to driving on an o2 sensor that is about to **** out. by the way i have a 97 ss about 65k ive done all the free mods and i have jethot LT's no cats and o2 sims for the back. i dont get it somebody please help.

 

Hmm that's odd... have you tried to just clean your 1 bad O2 sensor? Don't use any type of claning fluids.. just use a wire brush and clean it that way.... mine lasted alot longer after I did it. Just a small suggestion... good luck though!

 

The best way is to check the different readings for the ipw, injector pulse width, they should be very close to the same as you increase the rpm. a misfire really sounds like a bad plug or wire.

 

when you start your car cold the O2 mV should be around 450 or so on both sides.. that is what my car shows. i think its more likely the bad sensor caused a fouled plug or header leak fouled a plug.

 

It's not "low sensor efficiency", its low sensor activity on the passenger side precat sensor.

The O2 sensors will only show a relatively steady reading before the PCM goes into closed loop, or at WOT when the PCM is in power enrichment mode. Once the engine warms up, and the timer runs out (2-3 minutes) the O2 sensor should start fluctuating rapidly (approx. 9 times per second) between 0XX and 9XX mVolts.

If your sensors are giving you a steady reading, when the coolant is warmed up and the engine has been running for a few minutes, you have a problem..... could include:

-faulty extensions
-no voltage to the sensor heater
-bad sensor ground
-burned wires
-sensor wire too close to high voltage source (plug wire).

When they stay at 450mV, its because the wire is bad or the sensor is bad, and all the PCM can see is the 450mV bias voltage it supplies. But they shouldn't sit at 800mV at idle either.

 

well i checked the plug and plug wire and they are fine i dont really know how to check the injectore pulse width though. and my readings were from the warm up cycle i guess thats why they were steady. ill run it on the scanner at work again and tell you what they are reading after the 2-3 min warm up. i just dont get it though, it just seems weird to me you know. i have an A4 and i used to get with the shorties on and the new o2s about 240 miles per tank and now with the longtubes and the older o2s(the only ones that dont cause a miss) i get about 200 miles per tank with similar driving conditions and i didnt have any cats then. it does smell really rich though now with the longtubes and crappy o2s. but ill get back to you guys with more info. thanks for the help. joe

 

Exhaust leaks will cause the problem you are having. Poor extension wires will cause the problem too. Might be related to the LT install......

 

well the miss was getting noticeable even with the bad o2 sensors. the only reason it wouldnt miss is b/c it never left the warm up cycle. the lead tech at work thinks its a tuning issue though. ive never had it tuned though but he says with the new o2s its fluctuating like it should and the miss is intermittent in a few different cyl's. all the plugs and wires are good i do have an exhaust leak though both at the engine cause of bad gaskets and at the ypipe cause of poor welding. he looked at the ipw and said that once it warms up the ipw drops dramatically and is causeing a lean mix causing the misses. is he right do i need it tuned or is it the exhaust leak causing all of this. thanks again. joe

 

an exhaust leak will cause your car to run rich. if you know the headers are leaking then that needs to be fixed first. the O2 sensors read the amount of oxygen left over after the combustion process and either adds or subtracts fuel according to how much oxygen is present in the exhaust stream. so now imagine if fresh air was leaking in before the O2 sensors... they would see this really lean condition that doesnt actually exist and add more fuel than is really needed which would explain your poor fuel economy.

tuning your car isnt necessary with the few mods you have... the problem is your exhaust leak.

if you are having intermittent misfires then its probably still the wires arching but you cant see it with your naked eye unless you look at night. but again fix the obvious problem first which is the exhaust leak. if your motor isnt completely sealed up after the MAF and before the O2 sensors then its difficult to diagnose misfires and lean/rich conditions.

 

ttt