2003 Jeep Wrangler Sahara nightmare (ECM or O2 sensors?)

[03Jeeper]

Okay, I'm super new to this so bear with me...
I have a 2003 Jeep Wrangler Sahara. Well, my daughter has.
Anyhow, she launched a rod through the block. This was due to some problem that caused the check engine light to come on. Long story short... New motor is in and same problem:
The Jeep hardly runs when all O2 sensors are plugged in. I unplug the number one 02 sensor and it runs pretty good. Plug it back in and it hardly moves. ODB shows bank one lean and bank two rich.
Okay so here's where I'm at: Yes, I replaced all of the 02 sensors. Twice. Yes, I replaced the ECU. VERY expensive! Yes, I replaced the motor and intake manifold. Yes, four mechanics have looked at this at an additional cost of 4,500 and still no idea what's wrong with it.
PLEASE help... Or buy it from me.
Thanks,
Jim
@Wranglerfix

PS. This is an automatic trans, 6cyl.

 

[CharlesHS]

Check the wiring harness at the 02 sensors for chafes which can short to ground.
Check the wiring harness that is routed around the back of the valve cover and then around the threaded head stud on the drivers side. This harness comes from the ECU for communication to/from the engines sensors. The harness is known to rub against the threaded head stud and wear thru the split wire loom and wiring insulation causing the harness wires to short to ground.

 

[Wranglerfix]

@03Jeeper wiring gremlins tend to follow TJ’s. I would start by checking what @CharlesHS said. As I stated on the phone yesterday, I will refund your money if the ecm isn’t the issue. I know someone that will buy it if it comes to that as well.

 

[fizzlebottom]

What brand of the O2 sensors did you buy? It sounds stupid, but the only ones that work properly with these vehicles is NTK/NGK. Anything else will throw codes.

 

[Chris]

What brand of the O2 sensors did you buy? It sounds stupid, but the only ones that work properly with these vehicles is NTK/NGK. Anything else will throw codes.

X2 to this, it’s worth ruling out.

 

[JohnnySombero]

Totally agree on the O2 sensors. It’s an electronic crapshoot where even the good ones can be bad. I replaced all four O2 sensors on my daughter’s 06 with MOPAR sensors, which I was told are made by NTK/NGK. Cleared codes and all was well for about three weeks and then it threw a code for Bank 2, Sensor 2. I was not happy, but replaced it with an NTK/NGK. It’s been about a month and so far so good. These things can drive a sane man crazy.

 

[03Jeeper]

Awesome, thanks y'all. Monday I will pull it into the shop and pull all of the O2 sensors and replace with the NTK/NGK sensors. I noticed that they were slightly different. One has the notches or guides offset and one has them parallel. Anyone remember which is upstream and which is down? I'll check for a diagram as well.
Found the parts:
Part #: NGK 23141
Part #: NGK 23139
Part #: NGK 23142
Part #: NGK 23138
If anyone knows where to buy that harness, I'll pick one of those up too. Couldn't find on Amazon or anywhere else.

 

[Fishtaco]

Awesome, thanks y'all. Monday I will pull it into the shop and pull all of the O2 sensors and replace with the NTK/NGK sensors. I noticed that they were slightly different. One has the notches or guides offset and one has them parallel. Anyone remember which is upstream and which is down? I'll check for a diagram as well.
Found the parts:
Part #: NGK 23141
Part #: NGK 23139
Part #: NGK 23142
Part #: NGK 23138
If anyone knows where to buy that harness, I'll pick one of those up too. Couldn't find on Amazon or anywhere else.

I found this pretty helpful, I had it bookmarked.

 

[JohnnySombero]

Here ya go. The best TJ O2 sensor resource on the planet.

The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

What are Bank 1, Bank 2, etc.? Since this question pops up from time-to-time, here's an easy to follow diagram that illustrates what they mean when your OBDII code scanner (or manual) tells you something like "O2 sensor, Bank 1, Sensor 2": What does upstream and downstream mean? Simple...

wranglertjforum.com

 

[dogfoodboy]

I saw a reply to aone of these where the answer was plugged cats...it was a reputable member.

I'm from northern Nevada...

 

[Godzilla]

Okay, I'm super new to this so bear with me...
I have a 2003 Jeep Wrangler Sahara. Well, my daughter has.
Anyhow, she launched a rod through the block. This was due to some problem that caused the check engine light to come on. Long story short... New motor is in and same problem:
The Jeep hardly runs when all O2 sensors are plugged in. I unplug the number one 02 sensor and it runs pretty good. Plug it back in and it hardly moves. ODB shows bank one lean and bank two rich.
Okay so here's where I'm at: Yes, I replaced all of the 02 sensors. Twice. Yes, I replaced the ECU. VERY expensive! Yes, I replaced the motor and intake manifold. Yes, four mechanics have looked at this at an additional cost of 4,500 and still no idea what's wrong with it.
PLEASE help... Or buy it from me.
Thanks,
Jim
@Wranglerfix

PS. This is an automatic trans, 6cyl.

I had the same problem until I bought spark plug anti foulers , drilled one so the O2 sensor fit into it. I threaded it into a second fitting with the normal sized hole from the factory, and the put them into the exhaust bung holes . This will trick the computer regarding the 2 sensors after the catalytic converters into thinking the cats are working fine. As soon as I can, I'm installing a manual trans, and removing all the computer controlled engine stuff. I'd rather run a carb with an MSD distributor and headers, that keep farting around with all the electronic stuff. Send a message of thanks to the EPA for your issues !

 

[03Jeeper]

Okay, problem solved!
Big thanks to fizzlebottom, 03Jeeper, Fishtaco, and the rest of you guys for your suggestions. Also to @Wranglerfix for lending me the ECU to test that theory too. By the way, I FedEx'd your's back your way yesterday. It should be there by Friday.
Anyhow, close to seven thousand dollars later, it turns out it was the 02 sensors. One of them was most likely the culprit. I replaced all for with the NTK models as suggested and as soon as I started the Jeep the check engine light went off and it all of a sudden ran like a top! Smoged it yesterday with no problems at all! This is the first time in close to two years that the check engine light has been off. You would think that the damn thing would have burnt out by now!
Anyhow, thank you guys so much for the help! I decided to buy my daughter a new Jeep and keep this one for myself!

 

[Wranglerfix]

@03Jeeper I am happy you found the issue and I will be on the lookout for the Ecm! 👍🏻

 

[fizzlebottom]

There's so much more you'll learn from this forum juts by reading threads recounting peoples' experiences. Soon you'll feel like Connor Macleod absorbing all of the experts' powers and knowledge but without having to cut their heads off like the Highlander.

 

[Irun]

Congratulations on solving the problem! It's really bizarre how differently O2 sensors impact this platform. I went through this recently with a buddy, who was having issues with his Jeep randomly missing and, while driving, shutting down. When I asked him what he had done before, he told me he had replaced the catalytic converters and O2 sensors. Off course I asked which sensors and his response was "Bosch, because that's what I always use on vehicles". Long story short, I convinced him to swap the O2 sensors to NGK and his problem completely disappeared.

 

[The Bass Player]

I had the same problem until I bought spark plug anti foulers , drilled one so the O2 sensor fit into it. I threaded it into a second fitting with the normal sized hole from the factory, and the put them into the exhaust bung holes . This will trick the computer regarding the 2 sensors after the catalytic converters into thinking the cats are working fine. As soon as I can, I'm installing a manual trans, and removing all the computer controlled engine stuff. I'd rather run a carb with an MSD distributor and headers, that keep farting around with all the electronic stuff. Send a message of thanks to the EPA for your issues !

We used to do that in a repair shop I worked at when we would install aftermarket performance cats on vehicles.
I works very well.