Hi all. I have had this problem for a while and it's driving me nuts.

My 4.6 idles pretty rough most of the time. It also is using a lot of gas and seems to have a little less power than I'm used to. The truck has 100 000 miles on it.

So far I've replaced two bad COPs and the spark plugs last year. A scan shows no codes and the CIL is off. However, when I scanned the sensors the O2S12 O2 sensor is constantly reading 0 volts. This doesn't seem right as the other post cat O2 sensor reads a varying voltage. I'd guess that the sensor is bad but there is no code showing up. I also noticed that I have a slight exhaust leak in the joint on the crossover pipe.

Any suggestions before I start by replacing that O2 sensor?

 

First, fix the exhaust leak. That will hurt your power some and help your power when fixed.
If it still has a problem, look for a vacuum leak.
With 100,000 miles, it might be time to replace the front 2 02censers.

 

Thanks for the advice. I'm really curious why that rear O2 sensor is reading 0 volts.

 

The rear 02 sensors don't really do anything other then tell the computer that there their or not in there.
I run my truck with the back 2 turned off.
Not sure why it would be reading 0 volts.

 

Have you checked to see if its plugged in? Maybe simple as just cleaning the contacts.

 

Do you ever hear any rattling in the engine at idle or when accelerating?