Lurk

iTrader: (11)

ok

I'll be using the GMPP controller. For packaging reasons, will it work if I put the 2 O2 sensors BEHIND the cats?

This controller only has 2 sensors.

lsxm3

no you would want to put them IN FRONT of the cats so the ecu can see what the engine is running at for fuel ratio's. If you put them after the cats it will run like ****! this is due to the fact that it is the cats job to "clean" the outgoing exhuast and the readings will be much much slower and way off

cherryelky305

iTrader: (2)

yeah if you watch the voltage from pre cat and post cat sensors, the precat sensors are up and down all the time, then the post cat sensors are flat lined (thats how the pcm knows the cats are working)

Lurk

iTrader: (11)

Thanks guys! I understood that the cats clean up nox etc. I wasn't sure if it came out with a different o2 ratio than went in.

That was a great explanation Elky

cherryelky305

iTrader: (2)

i dont know how it works really? but the sensors show high and low voltage for rich and lean, then they flatline high or low if the cat is working right.

its really interesting how the pcm is actually just bouncing back and forth trying to keep the air to fuel ratio right.