Ok here is my problem. When I first bought this truck about 4 month ago I was very happy with it. It is a 2001 dodge ram 1500 quad cab long bed with the 5.9L. The first things I did was a tune up including oil change. Then I put bigger tires on it. Just one size bigger. Anyways my mpg when I first got it was about 13 with rough driving. I've now started driving more conservative and I'm getting 9 - 10 mpg. There has to be something wrong. My father inlaw has a 98 with the same engine and it get around 15. I'm assuming the first place to check would be the o2 sensor. Since they are 70$ a pop I would like to test them first. As you all know they arn't easy to get at. I found the manual for it and I'm thinking about testing them at the pcm. Anyways I've read alot of the other links here and found out about the cat being bad, and the gasket that blows out (I can't remeber the same right now). Where is the first place I should look to fix this problem. By the way when I bought the truck it had 111,000 miles and now its at 113,000. Anyways any suggestion would be great thanks.

 

What exactly did you do for the tune-up? What size tires did you go up to.....3.55 gears? Look into your throttle body and if there is oil pooled up in there your plenum is done for...a tiny tiny amount is ok.

 

I changed spark plugs, I recharged the KN Filter, oil change, pvc valve, and changed the wires. I went one size bigger on my tires. I beleive they are 285. I'm going to look at the plenum today

 

I have heard that the 285's will really bog these trucks down if you have the 3.55 gears. I am running the 265's on a 1500 quadcab (shortbed 4x4) and it runs pretty well on these. (I have the 3.55 gears)

 

That's whats bugging me so bad. My father inlaw has the same setup but it a 99 instead of an 01. He gets around 15 mpg

 

285's don't bog down 3.55's all that much. Still getting 12.5 to 13 mpg on a 9 year old 360 4x4.

ICEMAN_CH: Stop babying it.

 

my 01 has 285-75/16 and 3.55 gears. its a little sluggish and would benefit from lower gears, but i get about 15-16 mpg highway and about 13-14 city. if you are getting 9 mpg on regular road driving you have something wrong. its not the tires. likely an 02 sensor or clogged cat or something similar.

 

Is there a way to tell if the cat is plugged? I'm going to figure out a way to get at the o2 sensors. They are 70$ a peice so I'm going to test them first. I'm also going to check the plenum gaseket hopefully its one of those.

 

To check if the cat is plugged, pull the front O2 sensor and see if the truck runs any better. You can also try the whack test ... smack it with the palm of your hand and listen for rattling ... sometimes the guts disintegrate and you can hear it ... not a foolproof test but it sometimes works.

Oh ... wait until it cools off first.

 

one suggestion is to yank all the o2's (keep track of what went where front/back) and clean them. I have sucessfully cleaned about a dozen sensors all w/o any problems, motors ran better afterward too. My wifes corolla was getting a code for cat inefficiency, yanked both front & rear sensors, cleaned them up put them back and now 3 weeks later, no code. Use CRC electronic parts cleaner found @ the auto parts stores. spray the hell out of all the air holes in the sensor, let it dry and re-install. if the sensors were marginal, they will be working great afterwards.