One O2 Sensor 11% Higher...Why ?

[Vcoat]

Trying to get through my shortblock build and its been one issue after another...Shorblock was assembled with the stock heads, whipple 2.3 etc. Went on the dyno busted a lifter in half (passenger side). Heads rebuilt back on the car. Fired it up, one side of the exhaust breathing normal the otherside barely coming out at all. Blown cat passenger side. The stuff was jammed in the pipe. I cant believe how it was breathing at all. Cleaned everything out...hollowed out both cats. Now the tuner is getting this 11% higher reading on the passenger side O2 sensor. Could the sensor just be bad ? from all the extra heat generated from the clogged pipe ? There is also a small header leak at the manifold(stage 8 bolts will be retightned). Anyone have other ideas what could be causing the higher reading ?...Thanks in advance!
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MMR 5.0 Stroker, 2.3 Whipple. Mono TB, ST Motorsports Intake, Steeda 10 rib, 16psi

 

[avengence85]

Make sure there aren't any leaks. I would def try replacing the o2 sensor since they can go bad from too much heat. Better yet, switch the o2 sensors and see if the problem follows that sensor. If it does, then replace it.

 

[Vcoat]

Thanks for your response...tryed switching the 02.s and it was fine and then switched back it was good as well...now everything checks out but one side is still running lean...cam timing, injectors, coils, cylinder press all seems good

 

[avengence85]

Its got to be one of the injectors then. Take all the injectors off one side and put them on the other side and vice versa. See if it follows that bank of injectors. If it does, then mark them and move them one by one to the other side.

Reason I say one is because usually the o2 sensor isnt very fast so it might look like a consistent lean environment when maybe its only one cylinder. This way you only need to buy one injector.

Have you also checked all your lines to make sure there arent any leaks? Also made sure the intake plenum doesnt have leaks, especially on that side?

Also check your plugs one by one on that side. See if one looks like it has been running lean.

 

[StonePony]

When you are at wide-open-throttle I dont believe the O2 sensors are even used as the car is in closed-loop mode. Is the one side lean at WOT or partial throttle?