95 XJ 4.0 AW4 o2 sensor placement on custom exhaust

[Flamintrash]

I’ve got a 95 xj 4.0 aw4 upsized to 2.5inch exhaust with banks header. Just wondering about o2 sensor placement. Been having a stumble and misfire at 3000 rpm’s and when cold start.

Replaced or tested good
All sensors all clean voltage. Ones that were replaced were OEM mopar according to Napa.
vacuum leaks checked none found
Good fuel pressure
Timing good
No exhaust leaks
Injectors new and new pigtails
New air filter
Replaced exhaust gasket and throttle body gasket
Cleaned throttle body

Did change
Horseshoe intake
No cat
O2 sensor is placed right under the oil pan on the exhaust. Could be too far away from header? Anyone got some measurements? Ideas? Racking my brain to find anything else to do besides move the 02 sensor. Motor also only has 8790 miles on it. Trans has 175000 on it. Good clean fluid.

 

[Anak]

That is certainly farther away than stock, and the farther downstream the less desirable the location.

That said, it should be a 4 wire O2 sensor, thus a heated sensor, so the situation is not as bad as it would be if you were running a 1 wire O2 sensor.

Have you watched the O2 sensor values while the vehicle is running? A good scan tool might be able to give you the answers you need. Likewise, what is fuel pressure when you are getting the stumble. It is one thing to measure it at idle in the driveway, another thing to measure it at 3,000 RPM on the freeway.

You have also not said anything about what you have done in the spark department. Coil, distributor, wires and plugs could each play a role here. XJs are funny about prefering cheap plugs. It could be that simple.

 

[RCP Phx]

O² sensor placement is critical.
Within 6-12" of the collector
Not to deep or shallow penetration
Rotation between 10 and 2 O'clock
Square to the pipe

 

[Flamintrash]

That is certainly farther away than stock, and the farther downstream the less desirable the location.

That said, it should be a 4 wire O2 sensor, thus a heated sensor, so the situation is not as bad as it would be if you were running a 1 wire O2 sensor.

Have you watched the O2 sensor values while the vehicle is running? A good scan tool might be able to give you the answers you need. Likewise, what is fuel pressure when you are getting the stumble. It is one thing to measure it at idle in the driveway, another thing to measure it at 3,000 RPM on the freeway.

You have also not said anything about what you have done in the spark department. Coil, distributor, wires and plugs could each play a role here. XJs are funny about prefering cheap plugs. It could be that simple.

I have copper plugs new wires and distributor. Fuel pressure stays <1-2 within desired range during stumble. I don’t have a scan tool lol I should probably invest.

 

[Flamintrash]

O² sensor placement is critical.
Within 6-12" of the collector
Not to deep or shallow penetration
Rotation between 10 and 2 O'clock
Square to the pipe

Thanks much! I’ll move it and report back. Seen some posts about this but none resolved.