How's it going? Could a bad cat or o2 sensors cause my truck to run richer? Would it ruin o2 sensors and change timing and fuel pressure and then dump excess fuel into the cat and just make it worse until the cat is replaced? I ask because I'm getting my 4 cats cut off and replaced with 2 Magnaflows and I want to fix this problem so it won't happen to the new ones.

 

The O2's can make a truck run rich (theres usually a check engine light). On the cats, its usually the other way around....a rich condition will ruin them.

 

Ya see I haven't had a check engine light since a misfire on one my plugs a year ago. Now my cats are shot and I assume it's because of my truck running rich. I guess I'm going to have the exhaust shop take a look at my O2 sensors.

 

Oh and if I were to buy new O2 sensors, I would only have to buy 2 right? The ones right after the manifold? I'm looking at a manual on CD and it says those are "RH/LH Upstream Heated Oxygen Sensor (HO2S)" and the 2 after the primary cat are just "LH/RH Downstream Catalyst Monitor Sensor (CMS)." The CMSs only check if the cats are actually there right and the O2s would be the ones that would affect anything.