ConstantVelocity
New Member
Exhaust leaks upstream of the sensor can also cause them to indicate lean, and the PCM will add extra fuel in an attempt to compensate which (combined with free O2) cooks the cat. It would need to be a big leak to do this. I recall some years of 3.8s having issues with cracked exhaust manifolds, worth checking out. A missfiring cylinder will do the same thing. High fuel trims + dead cat points to unburned fuel and air getting through.
You could try swapping the injectors bank to bank, and replace the o-rings to rule out a leak there at the same time. Compression test too.
You could try swapping the injectors bank to bank, and replace the o-rings to rule out a leak there at the same time. Compression test too.