Change the cat and the O2 sensor.Sounds like that could be the problem. 5mpg?Wow,you sure no one is stealing your gas??

 

95Ram360, You said you use Mobil gas, is it the 10% ethanol? We have it here in Jersey and it #$%^&*# STINKS. Alot of people complaining about a loss of mileage and performance, and not just with Dodges either. While it might not be the total cause of you loss of MPG, it might be something to consider. Extended warmup/idle time kills MPG's. I found a StaBil product that seems to counteract the effects of the ethanol gas. Look for yourselves...
http://www.goldeagle.com/products/product01A7.aspx

 

Candyman no need to be a baby about it, im saying i know my truck inside and out, because alot of people will be like "oh that plenum may not look bad, but you have to take a further look into it" well i know its not bad, i check it every 3K when i do my oil changes.

wasnt trying to be mean about it, but theres no need for you to come and cry like a baby here...better yet just stay off the thread and prevent problems, because i have a bad temper, and if you say something else im going to flame you...cant help it thats how i am, so watch yourself.

but the 02 has been changed out. when i did plenum last year. but im thinking due to my cat breaking away on the inside, the 02 sensor isnt getting an accurate reading.

Truck idles perfect, doesnt flux in the slightest bit, no skips, never misses a beat, doesnt smell like its running rich, doesnt smell like anything honestly.

i going to get a snap-on scan tool hooked to it today and hopefuilly i can test some of the sensors.

 

What brand O2 sensor did you get?

 

dealer...

 

Hmmm, i think you may be right on the 02 sensor.

 

You'll want to address that rattling cat straight away so it doesn't cascade into a cracked head. That would suck.

Hmmm... lots of idling, scroungy cat, failing oxygen sensor, and winter blend fuel all combined might just be enough to hammer your mileage like that. First thing, though, is to get that cat taken care of and see what happens.

 

According to Mythbusters running heat or air doesnt use anymore gas than running with windows down. I would post tje link for that episode but i cant find it right now ill try to find it later. I do know that the heat only uses electric power from the blower motor it cant effect gas mpg in any way.

 

i would cut the cat off and just run a pieace of pipe in its place

 

He's in Massachusetts, he has to have a CAT.
It's just like California but with higher taxes.