What happened to my gas mi?

[Billieg]

Maybe someone can help me out here. I have a 1990 HR 35' with a 454 and 3 speed trans. When I first bought it I got almost 10 mpg on the way home not towing anything and unloaded. I loaded it up (not much at all for 2 people), no fresh water and pull an open motorcycle trailer with my Harley on it (not over 1,200 lbs total.

On my first trip I averaged 8.5 mpg. On my second trip I got 7.6 mpg and then had the motor tuned up with new plugs, wires, dist. cap, rotor, and the injectors cleaned. My 3ed trip I averaged 7.1 mpg and now my 4th trip I only got 6.4 mpg.... All 4 trips were here in Fl. where it's flat and the weather conditions and wind were about the same. What could be going on? I always do 55 - 62 so that's not it. I'm afraid to take it back out and see 5.5 mpg.....
Thanks for any replies.

[DriVer]

On my 2003 machine my MPGs began to tank when I developed a bad O2 sensor. Changed both! Not sure if this would help you at all.

[wa8yxm]

Try a wash and wax.. In another thead someone tells me that the improvement in MPG I got is a bit more than he believes... But .. Well, try it.

If nothing else it keeps the rig looking better so it is time and effort well invested

But you might be surprised at the MPG change too.. I was.

[tims52ford]

Could it be the ethanol in the fuel?

[JimElliott]

Quote:

Originally Posted by tims52ford Could it be the ethanol in the fuel?

Summer blend fuels will also drop fuel mileage..

Jim

[FreshAir]

With my 1989 34 ft Bounder w/454 I got about 7mpg towing or not towing. With my 1990 34 ft. Pace Arrow w/454, I got between 5 and 6 mpg towing or not towing.
FWIW.

[Dirtbuster]

Quote:

Originally Posted by tims52ford Could it be the ethanol in the fuel?

I agree!

[Billieg]

Quote:

Originally Posted by Dirtbuster I agree!

Thanks, never thought about the O2 sensor or the summer fuel. I'll have the sensor checked out. What's the difference in "summer fuel"? Here in Florida it's always summer....

I also washed and waxed the damn thing twice since I got it with all these love bugs.

[FreshAir]

on the 454 left side exhaust, driver side, about 3 ft from the exhaust manifold, before the left and right pipe y's into a single pipe, you may have a heat valve in the exhaust pipe that can stick closed. It's closed when engine is cold and opens on warm up. If it does not open your engine can't breath properly out the left side. Symptom may be an exhaust popping sound when passing like a Jersey Barrier on the exhaust pipe side of the vehicle. Just a thought.
Pat

[ronmc]

I had this engine set-up. 1983 Monaco. I got 6.5 to 7.5 average. And that's the truth.

[IC2]

Ethanol (10% or more) will hurt your gas mileage - and with some vehicles - significantly. My F350 - about 2 mpg in local driving. Gasoline has ~115,000Btu per gallon, ethanol is ~76,000 Btu per gallon. That means you will be getting 1.5% or poorer gas mileage at a minimum.

[ronmc]

Dave, With your figures, it seems it would be
a 34% drop in effic hiency.
76000/115000=64%

My mileage has dropped 1 mile per gallon,which is about 13%

[IC2]

Quote:

Originally Posted by ronmc Dave, With your figures, it seems it would be a 34% drop in efficiency. 76000/115000=64%

Ron, those are not mine but well published numbers by many sources. And remember, it's only 10% of the total (100%)

[Billieg]

Quote:

Originally Posted by FreshAir on the 454 left side exhaust, driver side, about 3 ft from the exhaust manifold, before the left and right pipe y's into a single pipe, you may have a heat valve in the exhaust pipe that can stick closed. It's closed when engine is cold and opens on warm up. If it does not open your engine can't breath properly out the left side. Symptom may be an exhaust popping sound when passing like a Jersey Barrier on the exhaust pipe side of the vehicle. Just a thought. Pat

Thanks, that's on my list to check too.