OK so i have an 2000 with the 4.7L. Replaced plugs about 1 month ago with the copper champion deals. After that could get almost 400 miles out of a tank. Ran some seafoam thru the gas tank 2 weeks ago and now it cut the mileage almost in half. Got only 230 miles out of the last tank. No check engine lite and no codes come up. Any ideas?

 

The last time I had a fuel economy change that drastic in one of my vehicles, it was because the odometer stopped working halfway through that tank of gas.

I'd do a quick check for non-engine related things. Are you sure nobody stole fuel from you? Odometer still work? Any fuel leaks?

Keith

 

I get about 260 miles out of a tank but I have the 5.2L. After you ran the seafoam, did you check the plugs?

I know when you run Seafoam through the intake, you need to change the plugs right after, because it burns up the plugs basically.

I would think even running it through the gas tank is possibly able to do the same thing. I would check the plugs, air filter, distrubtor cap, rotor, you know all the tings you would change in a tune up, and see if anything looks off.

 

chances are you fouled up the plugs, i would pull them and check em out, check gap and appearance

although please excuse me for this, but i find it VERY hard to believe that you get 400 miles out of tank even with the 4.7, unless are you are doing 100% highway driving without traffic, or you are running the tank almost dry.

 

( I wish my 4.7 would give 400 miles a tank)

 

yea my best ever mpg was 20.8 and that was a LONG highway trip on flat roads, no traffic and good weather (did NOT need the a/c that day), my light came on just over 350 miles on the tank iirc


date........odometer.....trip....gal...price...... ...mpg
9/26/06..... 54828....... 383...18.4..$2.14....... 20.8

i know these gas gauges arent the best, but if you run past the point the light come on you tend to be looking for trouble

yesi have all this information in a spreadsheet going back to the day my parents drove the truck off the dealer lot

 

ok so the 20.8 is the best that I have ever gotten out of the truck, apparently when my parents had it there was this in there


date........odometer.....trip....gal......price... ...mpg
6/5/05.......34849....... 515...19.2....$1.97......26.8

holy **** is all that i have to say . . .(this was before i even had my learners permit so it was one of my parents driving at this point)

 

holy $hit, they must've been driving down mt. everest or something.

 

HAHA @ that guy.....
Kinda cool you have info on the truck back that far though,talk about knowing a vehicle....a good thing there.OMG the 05 fuel price...imagine going back to $2 a gallon.
Back on topic,I bet you're right on the plugs sharp,although after running a detergent like Seafoam through the fuel system could've dislodged something..but it would run rough and trip a mil right? Maybe,as suggested,look through all tune up related itemsand fill the tank with untreated fuel,see if it comes back to normal.PLugs might be fouled/weakened,O2 sensor fouled/fouling....Why run detergent in the fuel in the first place,let alone after the plugs were changed?
Edit,One of the first things I learned from you guys here,and one of the best pieces of advice I gotten...Don't add ANYTHING to the fuel or oil in the Durango's,I'de say especially in an injected 4.7

 

Also... you may are a slight decrease right now due to the colder weather and winter fuel blend. My last 3 tanks (I fill up every 8-10 days) lost about 1 mpg (7-8%).