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Rough idle/running lean

There are many threads on different 4x4 forums that say Bosch O2 sensors and the Jeep 4.0 do not play well together. Champion Copper plugs are recommended.

NTK O2 sensors are what Jeep used and so should you.

JEEP P0171 Fuel System 1/1 Lean

Possible Causes

Exhaust manifold leak
Faulty front heated oxygen sensor
Ignition misfiring
Faulty fuel injectors
Faulty Mass Air Flow (MAF) sensor


Well I found the issue with the code, and the shitty idle, happened to be the Bosch o2 sensor upstream, replaced it with an NTK and everything ran fine instantly


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Are the ngk o2 sensor worth using in the xj 4.0 L ?

It is the one thing everyone seems to agree on. The Bosch ones go out. I just bought a NGK one off amazon for like $70.
https://smile.amazon.com/gp/product/B000C5M0Q0/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Summit racing also has it.
https://www.summitracing.com/parts/ngk-23553

A little less but it is probably special order. I ordered it before realizing I'm changing my exhaust gasket, and a motor mount while I'm in there so it's big work for me. to pass smog. on a vehicle I could register as exempt in 3 months.
 
It is the one thing everyone seems to agree on. The Bosch ones go out. I just bought a NGK one off amazon for like $70.
https://smile.amazon.com/gp/product/B000C5M0Q0/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Summit racing also has it.
https://www.summitracing.com/parts/ngk-23553

A little less but it is probably special order. I ordered it before realizing I'm changing my exhaust gasket, and a motor mount while I'm in there so it's big work for me. to pass smog. on a vehicle I could register as exempt in 3 months.


I usually put in champion coppers, but if everyone’s saying NGK...


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I, too had a P0171 code and saw that she was running rich...really rich. Gas mileage sucked. So I decided the upstream 02 had to be out or messed up. I ordered a NGK off of Amazon... https://www.amazon.com/dp/B001PNCKV8?psc=1&ref=ppx_pop_dt_b_product_details

It cost $36 or $37. I swapped it out, cleared the code and it has been running smooth ever since. The gas mileage improved dramatically as well.

My Jeep is a 99 XJ Sport, 4WD, A4 with the 231 and factory tow package with 3.55 ratios.
 
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