I'm new to the forum and i'm also new to owning a dodge ram. I'm above average with a wrench and have worked on many cars before but not a 4x4.

Anyways i have 97 1500 4x4 with the 5.2l 318 with 222,xxx miles on it. I'm the 3rd owner and my buddy who had it before me converted it from automatic to 5 -speed at around 190,xxx when the automatic puked. Even with the 5-speed and driving like a grandpa my fuel mileage is increasingly getting worse, i'm getting around 10-11 mpg right now and maybe 13 mpg on the highway. I have a flowmaster cat back dual exhaust, spectre intake, and a tonneau cover on it. In the past 2 months i've changed the plugs, wires, cap & rotor, and the plenum gasket. I've been religious with my oil changes and other usual maintenance. Is there anything else i could look into that could be causing my fuel mileage to consistently drop ? Thanks in advance for any help it is greatly appreciated!!

 

what size tires ya got on there?

 

265/75/16, they are 10 ply's but are almost bald and will be replaced here soon. Also while driving to work today on the highway my exhaust became very muffled but when i went on lunch break it was back to normal, then it got muffled again when driving home. I suspect my cat might be clogged or something else exhaust related. Could this be a cause to the crappy mpg?

 

If your plenum gasket is blown it will suck oil into the cylinders and eventually ruin the 02 sensors and plug up the catalytic converter. That would cause the bad gas mileage your getting as well as other problems.

 

02 sensors are going to have a lot of influence on mileage and should be replaced if original. New cat if you drove quite awhile with plenum leaking and burning oil. And going to 245/ tires might eek out a little more. Best I ever got was 14 mpg going 80-85 mph from Kansas City to Fargo. With one fill up in Sioux Falls S.D and an Arby's sandwich in the parking lot where JasonW/ moderator's signature picture was taken. My current ride gets 11.5 mpg combined. Aboout as good as it gets.

 

I was getting the about 10 mpg a few weeks ago. Now I get about 13mpg after changing the fuel pump. This is with a 5.9 and 34 inch tires.