O2 sensor cause misfires?

[shaggs_zerog]

I took my 03 Ex into a shop to pin point some problems, they corrected my lean/rich problem by doing a keep alive memory reset, but i still have a misfire on #2. They told me to replace both downstream O2 sensors and it should fix the misfire problem. Now, I talked to a ford tech online and he stated that the O2 sensors don't cause a misfire. I'm alittle confused on this one and was wondering what others here have done to correct a misfire, or may have some insight on rather or not the O2 sensors would fix my problem.

 

[02exploderguy]

Ok so an 02 sensor can cause a misfire...if it's bad enough.

Lets say it tells your pcm your lean the entire time. The PCM will keep richening up (if thats even a word) the fuel air mixture, so there is way to much fuel in the fuel/air combination. This could cause a misfire (by fouling out the sparkplugs or wiping washing oil off cylinder walls and wiping out piston rings)

or

If the 02 sensor tells the PCM that the mixture is too rich the entire time, then the PCM starts subtracting fuel and subtracting and subtracting, trying to get that 02 sensor to say lean. Well if all the fuel possible is being subtracted, then there isn't enough to burn. Those cylinders are down on power now due to lack of fuel = misfire.

It would be hard for me to believe that a bad DOWNSTREAM o2 sensor would cause a misfire on just ONE cylinder.

I am pretty sure that downstream o2 sensors monitor catalyst efficiency only. There could possible be a code set for downstream o2 sensor inefficiency due to the misfire and the cats are totally depleted of there oxygen reserves/or totally chock-full-o-02

Downstream 02 sensors ideally want to see the "perfect" oxygen content in the exhaust the whole time. all the time. If they see too much or too little 02 in the exhaust, too many times there will be a code for it. And that code pretty much says your catalytic converters are not doing there job.

But having that code doesn't mean your cats are bad.

And I'm almost 100% positive that a downstream 02 sensor won't cause a misfire on one cylinder.

Yeah a wrote a book, hope it helps though.

-Mike

p.s.-gimme some input on all this plz lol ANYBODY

 

[aldive]

Seriously doubt downstream O2 sensors are the problem.

 

[shaggs_zerog]

That does help. I've been banging my head against the wall with this one, the only code that's being pulled now is P0302, misfire on #2. I did have two fuel trim codes which were tooken care of when they reset the KAM(keep alive memory). As stated in my other post, I put new wires and plugs, and replaced one of the upstream O2 sensors.

I read somewhere that after market wires and plugs could cause a misfire, I do have auto lite wires and bosch plugs. I don't know how true this is.

 

[aldive]

Bosch plugs are not a good choice for an Explorer.

Many folks have reported problems.

 

[shaggs_zerog]

I got an update. Wed. at lunch I opened the hood and noticed the intake hose wasn't seated correctly(it wasn't pushed all the way up), I corrected that and there was no change in how the truck ran at that time. Yesterday evening the mis fire had stopped and the truck ran better. Today while doing my running around the CEL went off and it ran great.

 

[Quagmark]

Ok so an 02 sensor can cause a misfire...if it's bad enough.

Lets say it tells your pcm your lean the entire time. The PCM will keep richening up (if thats even a word) the fuel air mixture, so there is way to much fuel in the fuel/air combination. This could cause a misfire (by fouling out the sparkplugs or wiping washing oil off cylinder walls and wiping out piston rings)

or

If the 02 sensor tells the PCM that the mixture is too rich the entire time, then the PCM starts subtracting fuel and subtracting and subtracting, trying to get that 02 sensor to say lean. Well if all the fuel possible is being subtracted, then there isn't enough to burn. Those cylinders are down on power now due to lack of fuel = misfire.

It would be hard for me to believe that a bad DOWNSTREAM o2 sensor would cause a misfire on just ONE cylinder.

I am pretty sure that downstream o2 sensors monitor catalyst efficiency only. There could possible be a code set for downstream o2 sensor inefficiency due to the misfire and the cats are totally depleted of there oxygen reserves/or totally chock-full-o-02

Downstream 02 sensors ideally want to see the "perfect" oxygen content in the exhaust the whole time. all the time. If they see too much or too little 02 in the exhaust, too many times there will be a code for it. And that code pretty much says your catalytic converters are not doing there job.

But having that code doesn't mean your cats are bad.

And I'm almost 100% positive that a downstream 02 sensor won't cause a misfire on one cylinder.

Yeah a wrote a book, hope it helps though.

-Mike

p.s.-gimme some input on all this plz lol ANYBODY

I'm getting a P0171 code along with P0300, P0301 & P0303. The P0171 is system too lean and the other codes are misfire codes. The P0301 & P0303 codes are misfire of 1 & 3 which are on the right side of the engine, correct? Could it be that the O2 sensor is causing all of this, and if so would it be the upstream or downstream sensor?

I appreciate your help,
Mark

 

[Roy Martinez]

I took my 03 Ex into a shop to pin point some problems, they corrected my lean/rich problem by doing a keep alive memory reset, but i still have a misfire on #2. They told me to replace both downstream O2 sensors and it should fix the misfire problem. Now, I talked to a ford tech online and he stated that the O2 sensors don't cause a misfire. I'm alittle confused on this one and was wondering what others here have done to correct a misfire, or may have some insight on rather or not the O2 sensors would fix my problem.

The downstream 02 sensors only monitor the exhaust coming out of the cat, they do not control air fuel. the voltage once warmed up should stay pretty steady between 800mv to 900mv, the upstream 02 sensors are, or should be called air/fuel mix sensors as they are on Toyotas that I know of. The voltage on the upstream sensors should be moving up and down rapidly from around 100mv to 900mv and anywhere in between

 

[Roy Martinez]

That does help. I've been banging my head against the wall with this one, the only code that's being pulled now is P0302, misfire on #2. I did have two fuel trim codes which were tooken care of when they reset the KAM(keep alive memory). As stated in my other post, I put new wires and plugs, and replaced one of the upstream O2 sensors.

I read somewhere that after market wires and plugs could cause a misfire, I do have auto lite wires and bosch plugs. I don't know how true this is.

Have you even thought of the coil pack being the culprit? also be sure to use dielectric grease on the spark plug boots. I am a tech. many many coil packs