2003 Silverado 2500HD 6.0 P Code problems

[bredin]

Have a few questions, wonder if any of you have some ideas or input on them...

 

I have an 2003 Chevrolet Silverado 2500HD 4wd with the 6.0L Vortec (U code for VIN) and has about 179K miles on it.

The truck was getting a check engine code of P0101, MAF Sensor, I replaced that one and now I am getting the below codes, on and off...
P0131 Oxygen Sensor Circuit Low Voltage (B1S1)
P0151 O2 Sensor Circuit Low B2S1
P0327 Knock Sensor DTC Code
P0332 Knock Sensor 2 Circuit Low (Bank 2)

Everything except P0327 (normally stays on during normal driving) comes up when I floor the gas on the highway. But when going around 65 - 70 mph at 2000rpm, and gives full throttle, the truck down shifts to 3000 rpm first and then once more down to 4000 rpm, but there is no torque... truck actually slows down going uphill instead and does not go above 4000 rpm.

Should I bite the bullet and change the knock sensors and O2 sensors as well?
I got the suggestion that it could be clogged cats, but it's not idling or running rough...

Any ideas?

[davester]

It's pretty easy & cheap to test if the cat's are plugged, you test for how much backpressure is present at the upstream (closest to the engine) O2 sensor ports. You definitely want to do this test before shelling out for cat's.

 

Also check that all the bolts holding your exhaust manifolds on are there, as they break off and that screws up O2 sensor readings.

[bredin]

It's pretty easy & cheap to test if the cat's are plugged, you test for how much backpressure is present at the upstream (closest to the engine) O2 sensor ports. You definitely want to do this test before shelling out for cat's.

 

Also check that all the bolts holding your exhaust manifolds on are there, as they break off and that screws up O2 sensor readings.

 

Thank you sir, I will check this when the sun comes up over here again

[davester]

You might also check the fuel pressure. If the fuel pressure regulator or the fuel pump is failing, the engine will still run, but you will be down on power. There's a port on the fuel rail in the engine compartment for checking it. Check that the pressure is about 60 psi both at idle AND when the engine is revved. The pressure may drop a little, as the engine is revved, but should almost immediately return to about 60psi at the higher rpm.

[Justin101714]

Just pull out the O2 sensors and go drive it, that would tell you right away if you have a back pressure problem or not. It should drive better immediately

 

 

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