How to over-ride computer RPM while coasting?

[mcrews]

Originally Posted by ksa8907

As far as the engine revving while coasting in neutral, i would start by measuring the fuel consumption when idling (stopped) and when coasting.

this!!!!
Get a scanguage and do this test in about 5 minutes.

[mcrews]

it's easy to get fixated on something like this....had a tarsus that did the same thing.
But there are probably three other things you could do to get better mileage.
half of a quarter of a gallon OVER 1 hour is nothing.
maybe you can reduce the rpm in half, but it doesn't use twice as much gas to run 1500rpm (IN NEUTRAL). And honestly, how much time do you really spend coasting....

[oldtamiyaphile]

^That.

Also, based on my Wrangler and an expected 200,000mile life, I can actually buy a brand new Prius (inclusive of fuel and insurance) with the fuel savings. My Prius is actually 'free' as compared to using my Wrangler on a regular basis. I bought a used Prius so it actually 'makes' money. In fact I could even say I bought my Fiat brand new and the used Prius and got free fuel, with the fuel money from the Wrangler.

4x4's are awfully expensive to run. US figure will be a bit more SUV friendly I suspect.

[mmonce]

Originally Posted by ksa8907

As far as the engine revving while coasting in neutral, i would start by measuring the fuel consumption when idling (stopped) and when coasting.

that is a great thought. I have been considering a ScanGauge.

[mcrews]

there is a function call "fuel per hour" or "consumption per hour" that shows an instant continuous reading.
So one day you can coast down a regular hill and stay in gear, and the next day you can coast the same hill in neutral.
The you can see the difference.
Remember, the gauge is giving you a gallon/hour reading so you have to divide by the guestimate of the number of minutes you actually coast.
God Luck!
(ps you can buy a scangauge from this site!!)

[j12piprius]

Originally Posted by mcrews

half of a quarter of a gallon OVER 1 hour is nothing.
maybe you can reduce the rpm in half, but it doesn't use twice as much gas to run 1500rpm (IN NEUTRAL). And honestly, how much time do you really spend coasting....

Please clarify. If coasting in neutral at 65 mph & 1500 rpm is 400 mpg, wouldn't 750 rpm in neutral at the same speed be 800 mpg, which is half the gas and double the mileage?

[mcrews]

Same way that coasting at 65 at 1 rpm doesn't double the mileage from the 750 rpm. It's not a simple math equation. I would actually assume it is based on what is required to rim the engine. Engine load, gearing etc.
the issue, imho is consumption of fuel during the brief moments of coasting TO THEN justify a hack that might have unintended consequences.

[mcrews]

The bigger issue is: is it worth it?
Ecomodding makes sense on a older car.
But in newer cars, when there is so much pressure on manufacturers to I crease corp mpg, do you REALLY think that they have left MPG's on the table?
Look at all the trouble dodge went to to achieve class leading mpg on a truck! The actually have an active dispersion to lower the body 1" to improve aero at speed.
I would bet that Toyota has a reason for the rpm NOT to drop.

[Fat Charlie]

It may simply be to throw enough BTUs down the exhaust pipe to keep the cat running. Look back here:

http://ecomodder.com/forum/showthrea...ing-20338.html

My car failed CA emissions testing recently, and I'm confident my hypermiling had a direct relationship to the problem.

The failure was because some of the drive cycle monitor readiness flags hadn't been set since I cleared the check engine light/malfunction indicator light in October. Since then, I'd driven 800 miles, but the catalytic converter driving cycle is 15 minutes at speeds between 60-100 kph, and I hadn't done that in 4 months.

The next day, I warmed the car up, driving it enough to add 100 miles since the test failure. The car passed smog testing. Examination of the retest shows cleaner emissions after driving the car a distance at speed.

I drove the car 900 miles RT to/from SoCal last week, and the cat stayed lit, between 1101-1185 degrees F. When I do my normal low speed P&G, cat temps are 285-550 degrees F, too low to light the cat.

[j12piprius]

Originally Posted by mcrews

Same way that coasting at 65 at 1 rpm doesn't double the mileage from the 750 rpm.

I'm interested in your tests of coasting at 1 rpm, and how they support your theory that coasting rpm makes no significant difference to mileage. Likewise, please post some evidence that 3000 rpm, for example, is no worse for mileage then 1500 rpm, and whether this applies to gas use when idling at a stop, as well as when coasting.