I have a 2003 Ram with a Hemi and the guy I bought it from said it has a bad o2 sensor. I'm only getting 9mpg and power is definitely lacking. I popped under the truck to take a look and I noticed a ground wire running from the o2 harness to part of the frame. Why might he have done this?

 

o2 sensor should only have to wires. Vref and signal. A HEUGO which acts like a o2 sensor may have more. BUT one wire is not actually just a wire and can not be spliced. Why someone would ground it makes no sense. Unless they were trying to fool the computer somehow. What size tires on the truck?

 

Reason I ask is when I run my 315/70/17s I only get 10. If I run the stock 245s I get 16

 

They are just the factory rims and tires. What could that do to fool the computer? Could he be trying to cover up a problem thats more severe than just an o2 sensor?

 

What exactly is grounded? one of the 2 wires? or the sensor itself?

 

I'm not currently with my truck, im out of state. But all I noticed when I looked at it is that there was a black wire running from where the harnesses clip together leading to the frame