Well today i took the boat out (24ft deluxe partybarge). it was a 200 mile round trip to this lake hardly any hills down here in the south. now the tank is 20 gal tank and all i got was the 200 miles out of it. Now that means i am only getting 10 miles to the gallon. before i fixed the plenum i was getting at least 12/13 miles to the gallon.

anyone else notice a drop in fuel mileage after they fixed the plenum while towing

now it pulled like the boat wasnt even behind me so the power was restored, but damn why the fuel mileage drop.

 

First, do you mean you used 20 gallons out of the tank? Unless you did something special, 2500 quad cabs came with 34 gallon tanks IIRC.

Second, did you reset the PCM after you fixed the plenum (disconnect the battery for a bit)? That would cause excessive fuel consumption for a while as the PCM relearns everything.

Third, did you replace the pre-cat O2 sensor? The oil from the broken plenum usually kills it. A bad pre-cat O2 sensor will cause loss of MPGs, and like any other sensor, it may or may not trigger a CEL when it goes bad.

Fourth, are you sure you didn't just romp on it a little more than usual, since you have more power now?

 

are you saying you got 12/13 while pulling a 24 ft boat, or were you getting 12/13 while unloaded ?

 

I only pulled a 12ft utility trailer with a lawn tractor on it 5 miles tops and I went from 14.6 to 9.1 MPG.

 

no i didnt do anthing to the gas tas tank that is all that fits into the tank is 20 gals completely empty i wish it had a35 gal tank. The O2 sensor is new ,yes the battery was completely out of the truck during the fix, and i was doing the same speed as i aways did

 

Yes when loaded i was getting 11/12 no only getting 10

 

There is something wrong with that gas tank. The 1500 have a 26 gallon gas tank, so I don't know what the heck you got going on there. I don't know if it's even possible to get that much sediment deposit to fill up such a large part of your tank.

 

You must have the 26 gallon tank. I believe the 35 gal tank came only on the V10 and all long bed models unless specifically ordered. When the light comes on my gauge, there's 5 gallons left in my 26 gal. tank.

Frankly, putting around town, using AC, stop and go, in my 318 half ton I see about 11-12 mpg in the summer. With your 2500, pulling a boat, I'd say 10mpg is just perfect. Remember, you were also burning oil with your gas before so it used less.

 

My 1500 has a 32 or 35g tank- can't recall but, it's very large on my truck. If your losing MPGs, it may be that you have a clogged / partially clogged CAT and / or muffler due to the blown plenum. It also could be partially clogged fuel injectors or restricted fuel injectors at the screen.

However, it would run poorly in that case. I just had this happen this past weekend in fact. Rust from the fuel rails clogged them. But, if yours is running fine, it's not the injectors and I would look into your air supply at the intake and the TB to your exhaust flow. Perhaps the computer does not have enough data to fine tune for performance yet. I cleared mine out before running and was told that it takes a while to obtain an avg of all the sensors before it tunes in.

 

going from 12 to 13 normally to 10 with a pontoon boat sounds right to me. that boat catches a lot of air going down the road, its like riding with a parachute behind you the whole time. and my 26 gallon tank normally has 4-6 gallons left in it when i hit 1/8th to 1/4 on the gauge so i bet you have a 26 gallon.
do you fill up then reset the miles then calculate miles by amount put into the tank every time you get gas? that's the best way to do it, and if you do that every time then you'll know if somethings going on if you all of a sudden get 8 mpg.