96 5.7 Vortec having exhaust cat/ o2 sensor problems

[cody11aaron]

New to the group here, but seeking some advice/help. I have a 96 k1500 with the l31. Within the past month I've replaced the exhaust from the manifolds back with new cats and o2 sensors. When I got the truck back from my mechanic, it was running better than it had ever before (before as in glasspacks with no cats or o2's plugged in)... Until about 3-4 miles into the trip home, it lost almost all power like it was only running on half of the motor. When I got home, I unplugged the downstream o2 sensors and it ran fine again, it's only acted like that once with the o2's unplugged. Any ideas what this is or what to do? Thanks

 

[SAATR]

Downstream O2 sensors should have no affect on the engine's performance. Did they somehow manage to connect the upstream O2 sensor's connector to the downstream sensor?

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[cody11aaron]

I don't believe so, but I can try switching them. What about if one of the cats was plugged, maybe from a crack in the honey comb from shipping, would the unequal back pressure from the exhaust screw with it? The reason I say this is that I'm about 99% sure one of the cats blew out, going off the fact that when I got home that day there were small pieces of honey comb coming out of the drivers side exhaust tip...

 

[SAATR]

A defective catalyst causing an exhaust restriction could definitely cause what you describe, but there is no reason that unplugging the downstream O2 would cause it to run better. They are only there to check catalyst efficiency and set a code if the the catalysts aren't performing as they should. They don't affect how the truck runs. If you suspect a failure, pull the Y pipe and do a visual inspection to verify failure, or connect a back pressure gauge and perform a back pressure test to see if it's causing a restriction.

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