bad gas

Is the check engine light on? How many miles on this vehicle?

Chum lee

Fuel is going stale, you need to be sabilizing it. Seafoam at 1 oz to 2 gallons. Run the tank down below 1/4 tank, then fill it up to full with the proper amount of Seafoam, then drive it to get the mixture all the way up to the engine.

12th Man Fan wrote:
I think ethanol looses it's potency after awhile. I bought a new lawn mower lat year and the first thing they told me was to not use ethanol over 45 days old.

Yes I know a mower engine is a lot different but I suspect the fuel looses some punch even in a bigger motor.

I believe one issue is that the ethanol absorbs water. basically what Heet or dry gas is??? perhaps.
bumpy

You've got a problem.

I have the same engine and about the same weight motorhome and have averaged 7.1 mpg for the past 80,000 miles.

I travel in mountains a lot but have never seen 4 mpg. Lowest was about 5.8 on a day of continuous headwind and some mountains.

I have sometimes hit a 4-4.5 mpg as the mileage between fill ups, but next tank will give me 8.75. My 1999 (new at that time) gave me about 7.5 mpg.
Is the generator running, dash a/c and wonder how heavy the foot on the gas pedal? I usually averaged out 7.5 to 8.0 with a Class A, most always 31'.

I think ethanol looses it's potency after awhile. I bought a new lawn mower lat year and the first thing they told me was to not use ethanol over 45 days old.

Yes I know a mower engine is a lot different but I suspect the fuel looses some punch even in a bigger motor.

O2 sensor bad or dirty MAF

sea foam to the rescue
bumpy

4 mpg does seem pretty low, but mileage does depend a lot on the driving conditions, generator usage, etc. The worst case mileage you can get is zero mpg, when the engine is running and you aren't moving. I would generally expect something in the range of six or seven mpg, maybe slightly better, for a typical gas class A with typical (primarily highway) usage.

If you think you have bad or stale gas, the best advice I can think of is to use as much of it up as possible and refill with fresh gas. It probably would not hurt to put in some sta-bil before filling up if it will sit for awhile without being used. Depending on the mileage, it may also be worthwhile to do typical tune-up sorts of things on the engine: replace spark plugs, check and clean smog control sensors and gizmos, etc. It might also be wise to make sure you don't have any brakes sticking or dragging (though I think you would have noticed that independently).

4 mpg? That seems low.