NOT FIXED P0306 - 2002 Sahara 4.0 automatic (at wits end!)

[Rygrego]

Ok...so we know it works fine without the O2 sensor...right...

So perhaps we need to know if the O2 was actually the cause...or if not having the O2 plugged in forced the computer to stay in closed loop?

Here's my theory... everything works fine in closed loop...but you get a misfire on 6 in open loop...

Thoughts?

-Mac

Not having the O2 sensor connected would keep it in "open loop". Closed loop is full ECM control.

 

[Rygrego]

Ok...so we know it works fine without the O2 sensor...right...

So perhaps we need to know if the O2 was actually the cause...or if not having the O2 plugged in forced the computer to stay in closed loop?

Here's my theory... everything works fine in closed loop...but you get a misfire on 6 in open loop...

Thoughts?

-Mac

Open loop is the static program before the computer takes over. Closed loop is warmed up and under PCM control.

Ok...so we know it works fine without the O2 sensor...right...

So perhaps we need to know if the O2 was actually the cause...or if not having the O2 plugged in forced the computer to stay in closed loop?

Here's my theory... everything works fine in closed loop...but you get a misfire on 6 in open loop...

Thoughts?

-Mac

I figured I would get it to hard fault and upload the freeze frane data. Maybe it triggers something.

View attachment 534825

View attachment 534826

View attachment 534827

According to these readings the fuel system is not being adjusted by the ECM. (Not in closed loop).

 

[macleanflood]

@Rygrego excellent points and thanks for fixing my error.

All the more reasons I want to see what those O2 sensors are doing.

Something is keeping this engine on open loop...my gut tells me if we find that we get closer to a solution.

-Mac

 

[Rygrego]

An O2 sensor would would not throw or cause a misfire code (How could an O2 sensor cause a misfire code in one cylinder and not the others? There are two O2 upstream sensors each running 3 cylinders. If your still running a jerry rigged downstream sensor in place of the correct sensor put it back to normal. Down stream and upstream sensors are not interchangeable. I would try and see what the readiness monitors are showing and go from there. Some parameter is not being met and keeping the car in open loop. I would erase all codes and plug in a scanner the reads mode 6 and get an idea what's really functioning and what's not.

 

[Smokin151]

Mode 6 uploaded. Anyone see any smoking guns? I do see B1S1 failed!!

 

[macleanflood]

Shorted out O2s can mess with the 5v sensor voltage wacking out other sensors.

I think you've eliminated O2s as the cause. I welcome other opinions.

-Mac

 

[Smokin151]

I talked to Jay at Wranglerfix. I'm sending the pcm back to him. He is going to install on his jeep and see if he can duplicate it. He's shocked this has not been resolved, so we shall see!

 

[RocknLJ]

As luck would have it, I just replaced my muffler and tailpipe with a Banks monster exhaust on Sunday. All was well until today. Started getting a feeling of misfiring on acceleration and sure enough about 20mins ago after a ride code P0306 popped up after CEL illuminated.
I have an 06 LJR with a wiring harness loom that is deteriorating.
Will be digging into this later this week.
Thanks for posting all that you are going though and the suggestions from our fellow Jeepers.
I’m really getting tired of chasing all these problems.
Probably should just drop a Hemi in it….

 

[Smokin151]

As luck would have it, I just replaced my muffler and tailpipe with a Banks monster exhaust on Sunday. All was well until today. Started getting a feeling of misfiring on acceleration and sure enough about 20mins ago after a ride code P0306 popped up after CEL illuminated.
I have an 06 LJR with a wiring harness loom that is deteriorating.
Will be digging into this later this week.
Thanks for posting all that you are going though and the suggestions from our fellow Jeepers.
I’m really getting tired of chasing all these problems.
Probably should just drop a Hemi in it….

I just sent the pcm back to wranglerfix. I also sent them the mode 6 data with a detail list of checks and parts replacements. I will up next week when I get word back from them. Good luck sir! I hope you have an easier solution.

 

[RocknLJ]

I just sent the pcm back to wranglerfix. I also sent them the mode 6 data with a detail list of checks and parts replacements. I will up next week when I get word back from them. Good luck sir! I hope you have an easier solution.

Thanks!
Going to start with the plugs as they haven’t been changed in years. Figure to pull them and check what they look like and go from there.
Good luck to you as well!
Will post if I find a solution.