P0137 and P0157

I just bought a 2000 Silverado RCSB with a 4.8 and am having problems. I got troubles codes P0137 and P0157 (Heated Oxygen Sensor circuit condition)and it has almost no power. It has absolutely no low end and first gear takes about 10 seconds to get through. It has no misfire (that I can tell, no vibrations or movement) and every once in a while it will pull really hard like it should. It had a single chamber flowmaster and I thought maybe it didn't have enough back pressure so I swapped it for a super 40 with no change besides sound.

Today I:
Changed plugs
Used a can of Seafoam
Poured 2 cans of B12 into a full tank
Checked fuel pressure (holds at 50 psi)
Changed fuel filter
Fixed a cracked line going to pressure regulator
Pulled the fuel pump relay and ran a can of "Professional Injector Cleaner"

All with no luck.

The scan tool showed that the rear o2 sensors weren't doing much at idle but with throttle they picked back up. I have no idea where to start and don't want to blow money on something that isn't broken. Any ideas?

if you have access to the scan tool verify that the two front 02 sensors are cycling up and down. If one or both are not and are not cycling up and down around .100-.900 volts then they need to be replaced. They definitely need replaced if the readings are not moving.

How many miles? Almost no power could mean the engine is just worn out, the truck is almost 10 years old and I've seen engines lose all power at less miles. You may need to do a leak down test on the engine to determine the condition of the valves and piston rings.

The front two fluctuate like they should at idle and the rear two just stay around .100 until you start driving, then they will read closer to how they should. It has 135,000 miles, 13,000 less than my faster 4.3l.

the rear one does not affect emissions or engine performance, its just to test the catalytic converter's efficiency. Sounds like your cat may be plugged. Cut it off and see if it runs better. :thumb:

That's what I was thinking too, just wanted second opinion. I'm sure I can find a stock assembly somewhere online.... The inspection ran out last month but since I bought it yesterday I'm sure they will give me a while.

I am going to try a fuel volume test tomorrow and see if I can figure anything out. I have narrowed it down to either that or the convertors. Don't want to spend $300 and find out it is the other problem though.

50 psi sounds too low.

Rear O2's shouldn't cycle. Their sole purpose in life is to let you know if the converter is working or not.

You could try and unscrew your front O2's and zip tie them out of the way. Make sure no other wires will get scorched or melted from the holes you just put in the exhaust. :D You should be able to tell almost instantly if that freed up a restricted converter.

50 is a little low and Ricky will tell me if I already said that.

That 50 I came up with was before I changed the filter, maybe that had some effect. I changed 1 rear 02 sensor to see what happened and now I have the same 2 codes and a random misfire code. (The freeze frame for the misfire was at 0% throttle and 633 rpm while idling) Also, the truck does way, WAY worse while cold. Any idea what would cause it?

Vacuum leak from the intake gaskets is common cause of rough running cold. Injectors clogged with crap will miss at idle worse than on the road.