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View Full Version : Hang Time: Exploiting ECU Fuel Maps for Fuel Efficiency


BailOut
10-19-2008, 05:48 AM
I call this technique "Hang Time". I discovered it while driving cross country with a group of other hypermilers earlier this year. I first noticed it on the 1st generation Honda Civic Hybrid we were driving and then confirmed it on the 2nd generation Honda Civic Hybrid that we also had. Any engine that employs VVT/VVT-i or VTEC/VTEC-E definitely has this feature but so do many other vehicles, including the Ford Ranger. The only way to know for sure on a non-VVT/VTEC engine is to use a ScanGauge II to verify.

It's a fairly simple technique. Here's how it works:

While driving at a constant speed and in the highest gear possible for that speed simply back off the accelerator a "notch". You will notice that your RPM and speed remain the same but you have, in fact, invoked a fuel flow rate that is roughly 10% lower than it was. You can hold this throttle position for a long time, usually until you have to adjust for the terrain. This is why I call it Hang Time.

If you have a ScanGaugeII you can see this effect (and dial it in much better) by monitoring TPS, RPM and iMPG. When the technique is properly invoked you will see your TPS drop by a few points while your RPM and speed stay the same but your iMPG goes up by around 10%. For example, while driving on relatively flat ground at 55 MPH in 5th gear my TPS is at 26, my iMPG is around 50 and my RPM is around 2540. When I invoke Hang Time my RPM and speed remain steady but the TPS now reads around 24 and my iMPG reads around 55.

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From an advanced perspective this technique can be combined with a form of Pulse & Glide (P&G) to really crank out some great numbers. A ScanGauge II is required for a "Hang Time P&G" as the movements are too sensitive to guess at.

Once you reach a speed slightly higher than your target speed invoke Hang Time but instead of just backing off one notch go for two. Using my 55 MPH example above the TPS will read about 22 in the second notch. You will start to bleed off speed but just slightly so (maybe 2 MPH per mile), and your iMPG will read 30% higher than usual at this speed. Hold this position until you bleed off to 5MPH below your target speed and then push the throttle in just one notch. You will see a TPS reading of just 24 or 25 but you will begin to accelerate while still maintaining better than 45 MPG! Once you are above your target speed again back off to the second notch and settle back in while you glide again.

You will see different TPS readings at different target speeds but the formula will remain the same.

eco
10-19-2008, 09:41 AM
Good thread,Ive known this for awhile,you can also do this with your exhaust note,but since Ive got the new Magnaflow,its harder.

jronald
10-19-2008, 11:13 PM
Is this works to both A/T and M/T?

BailOut
10-19-2008, 11:19 PM
Is this works to both A/T and M/T?

Hello jronald,

It works with any form of transmission. It has been successfully tested on MT, AT and CVT transmissions.

jronald
10-20-2008, 01:41 AM
:thumbsup:
thanks.

samrawet
12-11-2008, 02:37 AM
thanks

stripey
05-27-2009, 05:57 PM
Nice tip.

snerism
07-11-2009, 02:14 AM
Very effective tip, thanks a mucho! =)

jhsouders
05-15-2010, 03:39 AM
WOW great thread, im going to try this tomorrow

imjustagirl8_05
08-11-2010, 10:17 PM
I want to know the specs of my Yaris, since I am not sure if my engine is VVT/VVT-i or VTEC/VTEC-E .. is there anywhere I can see my car specs? I bought it new in Jan 2007 if that helps...

nmgolfer
08-11-2010, 10:29 PM
It will work with your Yaris

http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=2007+Yaris+specs

Yaris Hilton
08-12-2010, 12:42 PM
I want to know the specs of my Yaris, since I am not sure if my engine is VVT/VVT-i or VTEC/VTEC-E .. is there anywhere I can see my car specs? I bought it new in Jan 2007 if that helps...

Your Yaris, like all U.S. Yarises, has VVT-i.

ibanezjeepguy
11-04-2010, 10:45 PM
have you or anyone else noted a difference in miles per tank back to back?
please repost with real world results as I believe scangauge are just real time estimates?

birdman
03-03-2011, 01:27 AM
Thanks!

Sparcoboy
04-25-2012, 03:18 AM
I've tried this but for me it wasn't worth the effort. Doing the same trip every day, I had to fuel up sooner with this technique. The problem is, I think, that in order to accelerate back to your higher speed you burn more fuel than you saved by lifting the accelerator a bit. As long as you're decelerating you burn less fuel, meaning more mpg but the time you accelerate you get only half the mpg's than before. For me driving at a constant speed has proven the best.

chaditotx
06-08-2012, 06:17 PM
I think its lag between the apps and throttle body.

libra23
03-12-2013, 01:33 AM
Hello Friends!
i have a problem, can you solve this?
I want to know the specs of my Yaris, since I am not sure if my engine is VVT/VVT-i or VTEC/VTEC-E .. is there anywhere I can see my car specs? I bought it new in Jan 2010 if that helps...

Sedan
03-15-2013, 05:42 AM
Hello Friends!
i have a problem, can you solve this?
I want to know the specs of my Yaris, since I am not sure if my engine is VVT/VVT-i or VTEC/VTEC-E .. is there anywhere I can see my car specs? I bought it new in Jan 2010 if that helps...

Toyota has VVT-i technology. Only type of Yaris not having VVT-i are the ones that can be run on leaded petrol. But I dont suppose you get leaded petrol in the US. Check the owners manual. It should be there. You also might see a sticky on the fuel tank cap reading "Unleaded fuel only". (Not sure if this is pasted in your country, but it is there in my Yaris)

Amdkt7
04-02-2013, 12:16 PM
I've tried this but for me it wasn't worth the effort. Doing the same trip every day, I had to fuel up sooner with this technique. The problem is, I think, that in order to accelerate back to your higher speed you burn more fuel than you saved by lifting the accelerator a bit. As long as you're decelerating you burn less fuel, meaning more mpg but the time you accelerate you get only half the mpg's than before. For me driving at a constant speed has proven the best.

Because of pumping losses the pulse and glide technique works. Hangtime is the same thing as pulse and glide. Some use extreme variations of pulse and glide, and it is tricky to know just how much gas to give it during pulse.

The reason it works is due to pumping losses (due to nearly closed throttle). The engine loses energy trying to suck air past the closed throttle). I'm not sure if hang time really works as the fuel does not get shut off like pulse and glide, but I see the same thing on my ecometer. If I time my glides according to the slope of the road I can really get a big boost in FE. During pulse the throttle is open wider, reducing pumping losses, and the engine operates more efficiently.

I'll experiment with hang time some more. I was noticing the same thing, but have not tried to exploit it.

ardvark2175
10-29-2013, 04:09 AM
Bought a 2012 Yaris LE automatic. I was pretty much getting the advertised fuel economy of 32 / 35. The following service was done to the vehicle. 50 miles at purchase, installed K&N washable air filter. 500 miles, oil change standard Valvoline 5w30. 2500 miles, oil change with standard Valvoline 5w30. 5000 miles, oil change with Semi synthetic Valvoline 5W30, cleaned air filter. 10000 miles oil chance with full synthetic Valvoline 5W30, transmission flush with AMSOIL Signature Series Fuel-Efficient Synthetic Automatic Transmission Fluid. Immediately after going full synthetic I gained 5 mpg. I get 40 mpg regularly now driving the same 180 mile route driving 60 and 65.

dj92
11-13-2013, 08:11 AM
I think this trick is based on the acceleration enrichment.
It's used to let the engine pull stronger when you want to accelerate, and by releasing the pedal a bit, the ECU stops this enrichment which results in a better MPG.
It did not really work for me, shifting to the 5th gear from 18MPH on improved my in-town MPG this morning from 47 to 49.
However, my record on a level road outside the city was 58 :)