??

since learning that fuel is cut off while coasting in gear, and it has to be on to idle out of gear, i've been coasting in gear a lot... but sometimes my scangaugeii goes to 9999mpg, and sometimes it doesn't - it just caps out at 50 or 60 or 80mpg/whatever.

i didn't realize why until i read a thread on another forum today re: hypermiling. there's apparently a certain rpm for each motor with fuel cutoff where the fuel gets cut off, but if the rpm is below that fuel is still injected.

so, if coasting in 5th gear means you're still below that rpm, it's more fuel efficient to coast in 4th gear at an rpm above the "overrun cutoff rpm" (as it's called) in order for the fuel injection to be cut off, attaining infinite mpg as no fuel is being burned.

anyone know what the specific rpm is? i'm sure i can figure it out via trial and error & paying attention... but if anyone knows, it'll help some of us save a a few cents worth of gas sooner rather than later. plus there seems to be a bit of a competition to see who can squeeze the greatest distance out of a tank... and if i save more pennies i can spend it on :beer: :D.

try this.....

when coasting at about 65 or 70 mph, take it out of gear (neutral) and let the engine idle while your still moving...

look at your scan guage.....

whats your mpg?! prolly about 150-200mpg.. pretty sweet..

sorry this doesnt answer your Q, thought i would share..

mpg apearrently have something to do with RPM vs MPH....higher speeds with lower rpm, better mpg...

Does your SGII have the fuel cutoff setting and if so, what's that set to? Reading on sites like cleanmpg.com the general consensus is to put its value at 1 above what your TPS reads at idle. IIRC, the TPS on mine bottoms out around 6 or so. I don't have this option on the first gen ScanGauge I have. That may help you figure out if you're going into deceleration fuel cutoff.

I'm wondering when watching the open/closed loop display, if it goes into dfco when it switches to open loop? If I let off the gas and begin to coast, the MPG spikes up and it goes into open loop mode then goes back into closed once I give it some gas.

I don't know what the optimum speeds/RPM's are for in-gear coasting but without a doubt that's one of the best things I've found to do with this car to bump up the FE. I'm scared to crap of tearing up the transmission, so I'm not doing any pulse and glide (per a TSB on hmaservice, no FWD automatic Hyundai can be flat towed, so if I kill the engine at speed the pump won't run in the tranny to circulate the fluid.) Manuals are OK to be flat towed, so P&G may be an option if you so desire. I tried engine on coasting in neutral but when I put it back into drive, there was too much drivetrain shock for my liking (I didn't think to rev match, oops! :P) So, I'll just leave it in drive and let off the gas. I can easily get 40-45 MPG for my commute home by doing a lot of coasting since it's all a downhill ride going from 700 ft to 400 ft elevation over 16 miles. To work sucks, mid 30's or so for the uphill climb. :(

I dunno, I'm just in the learning phase of this hypermiling stuff. What I've seen so far can really work though! :)

I just throw mine in neutral, when coasting down hill .. when i go back into drive i dont press the accelerator untill i feel the gearbox start to drag.

I have never heard of a fuel shutoff except for top end speeds which is upwards of 125 on our accent.
Otherwise if the ignition is on and the engine is running fuel is being injected at a rate to sustain ignition to proctect steering ability and transmission clutches.
In nuetral it allows the powering steering pump to operate at normal idle speed and circulates fluid in the trans. enough to avoid overheating.
In gear you would experience "overrun" when the speed of the vehicle being driven reaches the point of being above the speed of the force driving it.Resulting in disengagement of the torque converter to avoid the car driving the engine and using gas enough to sustain high rpm operation,gas build-up in the exhaust system,backfire,severe drag.I was under the impression that the this allowed the idle system to take over.
For example older model automatics.You could cut the switch at speed ,coast a few secounds, and turn ignition back on ,resulting in a superloud explosion of built up gases in the exhaust system,and a few exploded mufflers and sound ordinance tickets. :ph34r: Not that I have ever done that.LOL
Maybe this is where the dfco is now iniated to prevent such results.
If this is true then as long as your tach is reading above idle speeds,(while coasting) you should be in the zone of the cutoff.When the tach goes to idle then the converter disengages and you are on idle fuel flow.However until the disengagement f the torque converter you will feel engine braking affect.
JMTC :whistling:


This post has been edited by Tango2Go: Jun 1 2008, 05:21 PM

the fuel definitely cuts off while coasting in gear. think about it... the engine can continue under momentum + gearing, just like push starting a manual car if your starter has crapped out.

i paid closer attention to the cutoff point while in 4th & 5th gears. it seems it's got to be a bit over 2000rpm to cutoff initially, and then will stay off until it's down near idle rpm.

i don't think paying super close attention to it is going to have much affect on mileage. maybe 0.1mpg difference, if that. i think the biggest related improvement is going to come from coasting in gear vs. in neutral.

right now i'm about to set a new all time distance on a single tank record for myself... i'm at 571kms/355miles & the low fuel light hasn't come on yet! (granted, i top off to the top of the filler neck.)

Yeah for manual transmission cars leaving it in gear lets the wheel power turn the engine instead of just idling which saves gas unlike an automatic that idles when you let off the gas, i would guess that at around idle (800rpm?) is when the ecu starts to supply fuel again for idling i usually downshift at around 3k rpm so i can keep my car in gear until im at a complete stop, then i let it idle before it dies out.

On the highway, the RPM's drop very little on my automatic when I let off the gas. It only drops down to idle speed if you've slowed to a stop or throw the thing in neutral. :grin:

I have heard that some cars with automatics will drop to idle speed when you let off the gas but mine doesn't.

That's what I was speaking of earlier ,from experience with older model cars.I have to admit I really hadn't paid much attention until you guys mentioned it.Mostly because I had never heard of the dfco before.Though it did make a lot of sense to put it in nuetral years ago now it would be more beneficial not to.That's why I like it here ,you can actually learn stuff w/out the wise*** remarks found on other forums. :thumbsup:

HEY! there is some pretty good wise **** remarks on here... mostly to do with nothing or an exact opposite but we still talk nonsense :57:

there wasn't a healthy dose of shenanigans on this forum you can bet your **** i wouldn't read it.

Yea ,but there is a difference between wise *** humor and Smart *** rude. :P
No harm in a little good humored ribbing,but there are some real a***s on some of the other forums.

i see you've found my other usernames on other forums... :P