Vehicle stops fuel trimming at WOT

[dbeau]

I’ve been trying to sort out some performance issue on a new to me 2004 Pathfinder. Watching O2 sensor and fuel trim data I haven’t figured much out yet but I have noticed something weird.

Under WOT the O2 sensors basically flatline at .8v and fuel trim stops all together reading 0.

Anyone know what this could mean?

Thanks

 

[mattd]

That’s normal.

 

[JRay’07]

Full throttle enrichment for maximum power!

 

[Rand]

Operating as intended. WOT is different than partial throttle.

 

[dbeau]

Well alright... That's good. Thanks.

I guess I'll expand on the issue then hoping for some feedback.

There is a sort of hesitation from about 3k rpm to 4k rpm where it runs very rough and accelerates slowly. Even to the point where in higher gears on an incline it won't accelerate at all. It'll just sit at about 3200k or so even slipping or bucking slightly. If i push through it once it hits 4k rpm it's smooth and runs like a bat out of hell.

There are no codes related to misfire. Only codes are for bad cats (downstream O2's not happy). I don't know if this is a transmission thing or if it's some kind of intermittent misfire. I've changed the trans fluid when I first got it and plan to again soon at OCI.

Thought? Thanks.

 

[Trav]

As others have said normal operation for old type O2 sensors, newer wide band O2 controls the ecm even at full throttle. A bad cat may be causing your running issue, check for exhaust back pressure at the front O2. You can find cheap testers like these from Amazon, better ones will use a steel braided hose.

https://www.amazon.com/exhaust-back-pressure-tester/s?k=exhaust+back+pressure+tester

 

[Mechanician]

As others have said normal operation for old type O2 sensors, newer wide band O2 controls the ecm even at full throttle. A bad cat may be causing your running issue, check for exhaust back pressure at the front O2. You can find cheap testers like these from Amazon, better ones will use a steel braided hose.

Try blocking off the EGR valve hose, and test drive it to eliminate that system.
Higher mileage EGR systems can become blocked to some cylinders, and overload the rest.
EGR works mid-throttle. (But usually before 3k RPM.)

 

[Luftmasse]

I’ve been trying to sort out some performance issue on a new to me 2004 Pathfinder. Watching O2 sensor and fuel trim data I haven’t figured much out yet but I have noticed something weird.

Under WOT the O2 sensors basically flatline at .8v and fuel trim stops all together reading 0.

Anyone know what this could mean?

Thanks

At .8V means it is going into full enrichment due to WOT. At WOT, the system goes into Open Loop mode temporary which the computer does not compensate for the fuel trim until it goes back into Closed Loop.