Exhaust pressure
#2
Yes it can have 3 cats. Two would be precats and then the you'd have the catalytic converter. It depends upon what emission package you have. Only the precats are monitored by the PCM.
You can check back pressure with a vacuum gauge. Hook it up and read it at 2500 rpm or so. It should stay steady. If it drops you have an obstruction.
You can check back pressure with a vacuum gauge. Hook it up and read it at 2500 rpm or so. It should stay steady. If it drops you have an obstruction.