I have a 2006 dodge Dakota st with the 6sp trans. it has about 220k on it and at about 190k or so the fuel mileage began a fairly quick drop from about 26-28mpg down to 14-16mpg. Since then I have changed the plugs and the iat sensor. I would like any ideas on what could be causing this. I've been told it could be the catalytic converters amongst many other things. If it is the cats, how could I check this? and is there a mod that could bypass the o2 sensors so that I can run without cats? thanks

 

I assume it has the 3.7L? I've never seen mileage that high, ever. These trucks are just too heavy for it, and like parachutes. Are these hand calculated numbers or using the overhead display? were the numbers done using (the only correct) method of miles driven divided by gallons put back in?

My mileage always goes down in the winter months, I don't know where you're from, but it's been so cold here I've had to idle to warm it up so my kid doesn't freeze when I take her to school before work.

Do you have any check engine lights coming on? These systems are pretty sensitive to catalytic converter problems, a code should pop up if they are going bad.

about removing the cats, the trick is to get some sparkplug foulers, bore one out, stack it on another, and thread it into the bung. This will hold the downstream O2 sensor away from the dirty gases and trick it in to thinking it's cleaner.

 

Maybe someone is sneaking up to your truck at night with a gas can and a piece of hose?

 

Welcome to DF. I have to second the mileage thing. The 14-16 is about average for the 6 cylinder. FrenicX is also correct about the winter mileage thing. Running without cats is not recommended imo. They are there for a reason. Plus if you have inspections, you will fail. That being said, lots of people do it. The only failure that would cause a drop in mileage is if they were clogged, but then you would have a bunch of other driveability issues. Lack or power, etc, plus the CEL should be on. With 220k on it, I would suspect your O2 sensors. Try replacing them first.

 

I have been checking the mileage by the gallons it takes to fill up and the miles. It does a little better in the cool weather. I am in south texas tho. I appreciate all the input. I'd rather not mess with the cats. I will try the o2 sensors. There is no CEL on. The truck runs pretty decent. once in a while it wants to spit and sputter on jack-rabbit starts. and sometimes it will start and die but it starts right back up. If anyone has any other advice about this issue i'd be glad to hear it. thanks again y'all.

 

I know my dak died on me a few times before taking to the dealership... Fuel lines were clogged and I had strayed from mopar spark plugs, clearing the lines and injectors and replacing spark plugs did the trick haven't had a problem since.

 

best trick I ever did was swap out those crap mopar fuel injectors and replace them with ford injectors, they have a much better spray pattern for the nitrous

 

Well, I have a 6 speed manual transmission with the 3.7L that I bought brand new from the dealer back in 06. In 148K I have never hit anything over 22mpg. With the lift, 33s, no aero, CAI, exhaust, and E-fan, I get 18mpg blended between half city/hwy driving. I get 20-21mpg on the highway.

The first thing I would do is run a can of BG44K through the fuel system. That stuff is the best fuel system cleaner to use, but it will also clean your cats and O2 sensors. After that treatment, I would get a tool that measures data in live timing (some code readers have that feature) and log your injector duty cycle, and percentages on bank one and two. If you are seeing anything above +10% on your short term fuel trims, I would start looking into a process of elimination.

 

I hit 22 once with my 4.7L V8, granted the newer 2008+ engines are a tiny bit better on fuel than the older 4.7.

However, that 22 was doing about 60 MPH and with no wind, which is a rarity out here on the plains.