Interesting development. Details first.
2004 Discovery 143,000 miles
Rebuilt top end 2000 miles ago to include:
Timing chain and gears
Oil pump
Water pump
Crower cam and lifters
Heads decked and pressure checked.


Been running like a top until this week. Popped a P0134 code so just replaced all four o2 sensors as they looked original. Code went away until today. Started watching o2 voltages on ultra gauge and noticed showing lean on bank 1 sensor 1 and rich on sensor two while on the highway (.235 and .900 plus). Sensor 1 just stays around 200-300 until I get off highway, within 1/2 mile goes back to normal.


Thoughts?

 

Swap the front o2 sensors and see if the code follows, if it does then you probably bought a faulty sensor.

 

Tried that yesterday as well. No exhaust leaks as well. Not sure where to go now as all plugs and wires are brand new as well.

 

There are a couple other possibilities.

It may be a coil pack, these are pain cause they are a bear to access, even for testing.(Although you will usually get a missfire code when these go).

If you have a secondary air system the vacuum valve on that side may be stuck open and letting air into your exhaust system.

Just my 2 cents.

What I really wanted to know is were you got you Crowler Cam, I am about to do lifters and rods on my beast and its probably a good time for cam as well.

 

Great idea, thanks will take a look at that when I get home. Not getting any misfiring just the occasional stumble due to it changing the air/fuel ratio.

I got the cam and lifters from Mark at D&D Fabrications: Engineering & Fabrication Services. Great guy to deal with. Also did the ARP studs for the heads while I was in there.

Really like the cam from Mark. Good low end torque and gas mileage is a little better.