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Old 04-05-2013, 09:49 PM   #190 (permalink)
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Join Date: Apr 2011
Location: Muskegon,MI
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The Beast - '93 Fleetwood Flair includes kitchen sink
90 day: 9.2 mpg (US)

The Bigger Beast - '03 Winnebago Sightseer Motor Home
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Originally Posted by LostCause View Post
I don't think you'll be able to maintain 40mpg going up any long, steeply graded hill...going slow works to a point.

If it is constant throttle you seek, why not just hook the throttle servo to a potentiometer.

I'd imagine using a cruise control based on MPG might pose some dangerous situations. A car will shift its speed greatly as it is loaded differently throughout a drive. I can't imagine that driving 65mph, slowing to 40mph, and speeding up again to 60mph would be particularly safe in any form of traffic. If you are completely isolated, then I suppose it might be useful, but not as a daily use item.

I'm interested in watching any developments, though.

- Lostcause
I drive a large 26 foot motor home . Look for the Beast in the garage.

I have installed a MPGuino and Jcar module to monitor the fuel usage.

I get about 10.5 mpg using E10 fuel. The fuel mileage has gone down over the 5 years I have lost it because of the E10 gas.

Now, how do I make good use of the MPGuino? I now use my right foot except on very long flat roads I use cruise control because it isn't a reason not to

During acceleration the RV mileage starts at about 1.25 mpg. Each time it shifts up the mpg gets better. I have a 454 Chevy with automatic trans w/overdrive and lockup clutch. I accelerate as quickly as necessary.

Once I am in high gear I level off the gas at 50 mph. If the fuel is good, I can tell that right away. Once I have leveled off, I will check the instant mpg and keep an eye on it and the road.

Most cars and RV's are Fuel Injected engines and run on several modes depending on speed and load. One mode is acceleration. This mode adds fuel for more power. So don't accelerate! At least not up hill.

The desired mode is Lean Burn. The lean burn mode is descriptive, the ECU tells the FI to lean out the fuel. The engine likes lean burn but won't stay in it for long. Any small rise in the road will cause it to go back to normal fuel burn.

If I slightly release and press back down on the throttle the lean burn mode will come back. This is a very small release. I see 1.5 to 2 mpg more.

Here is the neat thing about lean burn. The ECU sees throttle position, manifold vacuum, air temperature and many other signals. When I am going up a hill I have found that if I hold the throttle very steady the fuel mpg will hold as well. The mpg will slowly go down but not go out of lean burn. If I wiggle the throttle the mpg will drop. I quit holding the throttle at 40 mph and press down for more speed. Then the fuel mpg will drop to 3-4 mpg. I was holding 10-12 mpg going up the hill.

Having the MPGuino has allowed me to watch for the best speed to go. The engine torque power curve gets strong at 1000 rpm and peaks at 1400 but it is very flat. The horsepower curve starts at 1000 rpm and peaks at 3600.

This is right in my speed range, cruising at 50 is about 1600 rpm. At about 3000 rpm I run about 70 mph.

This tells me that if I go faster I could get better fuel mileage by driving faster. This is because the engine is "On the cam" and getting better efficiency. That is is true, showing 10-12 mpg at 62-65, on lean burn, but I am usually slowing down. A tail wind really helps! I now do a pulse and cruise in and out of lean burn.

If I see a large hill before me I slowly increase speed. On an expressway I can go up to 70 mph. Once I encounter the hill I hold the throttle steady and go up the hill. My fuel mileage will stay steady since I had gotten a "head start" going up. I like to see 10-12 mpg while going over a big hill!

By watching the traffic and the terrain I can chose when I pulse it faster or let it cruise.

Because E10, E15 fuel is so bad, I am going to pure-gas. Known as E0 fuel. There lots of stations supplying it. I find it on Since I can go about 700 miles on my RV per tank full, I can plan out my gas stops. I can route right to the fuel stop with my Delorme Street Atlas GPS map. My RV has a 75 gallon tank. No, my MPGuino still hasn't had a proper calibration YET! it's getting real close though.

Ever get water in your fuel? With E10 in the tank the ethanol is very hygroscopic, meaning it sucks water right out of the air! That's why I am going to get E0 gas. E0 = No ethanol in the fuel

On my trip to Florida I noticed that the engine would sometimes die while running on the road. I knew what it was so I put more StarTron fuel treatment in. I didn't know how much water was in the tank, but the StarTron wasn't powerful enough to remove all the water. My guess is I had at least a quart of water.

I got stuck in Atlanta's famous rush our traffic when the engine died while going slow. This time I couldn't restart, and used up all the ether starting fluid I had. Now the starter died as well as the nose gear wouldn't engage.

With a $565.00 tow truck ride to Marietta GA to Georgia RV service, I got it repaired. New starter, new fuel filter. I still had lots of water too. No way of getting it out.

Anyway I was able to go south and watch the Detroit Tigers win some ball games.

Now you know why I HATE E10 gas!


Last edited by CrazyLee; 04-05-2013 at 09:58 PM..
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