Hang Time: Exploiting ECU Fuel Maps for Fuel Efficiency

[RningOnFumes]

Food for thought for those of you with late model cars:

Hang Time: Exploiting ECU Fuel Maps for Fuel Efficiency
--------------------------------------------------------------------------------

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.

----------

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.
__________________
- Brian (BailOut of YarisWorld)

Notes:
*Works on cars other than the Yaris.
*For EFI mostly, but does not matter Manual or Automatic Tranny
*Nice if you have a SGII, but not necessary. You can still experiment for best application of your technique, just might take longer for results to show.


Discuss.

[touringcamry]

Interesting concept but I'm not sure I can use it due to the terrain on local highways. We don't anything flat like 210 here.

[RningOnFumes]

You're right, you will be mostly doing DFCO (deceleration fuel cut off). Aren't your free ways just as flat? Then again, I know you travel mostly inner city.

[touringcamry]

The freeways here, both within SF and outside have quite a bit of elevation change - even if it's 50 ft over .50 or 1 miles so it's not completely flat. Remember that I am more or less on the Pacific rim so there are lots of hills and mountains.

The freeway that I use mostly is I-280 which has quite a bit of elevation change. There is a flatter route, US-101, that parallels it but it's generally more congested, because it passes through more urbanized areas, and the roadway is more dilapidated. I-280 has more hills and turns but doesn't have nearly as much traffic and the roadway is in better condition.

In inner city driving, the freeways are on the other side of the city so I don't use them often. Most inner city driving is on local streets which still have elevation change. Normally I exploit fuel cut, coasting when anticipating red lights changing to green, and control my right foot. If there are stop signs every 300 ft I might only accelerate to 20 MPH or less and coast the rest of the way in 2nd rather than quickly accelerate to 25 and then hit the brakes.

There is a roadway here that goes for about 2.5 mi, speed limit 35. There are stop lights approximately every 1000 ft that are synchronized. It used to be that you could drive 35 the whole way but it's slightly slower than that now because half of them are all direction red for 2 seconds or so. If I'm the first one, I can drive without using brakes the whole way. Usualy though, people quickly accelerate to 35 MPH+ and then stop at the next light to repeat the same thing. If I'm behind someone like that, I just set the cruise control to about 30 MPH because I have to wait until they get their cars back up to speed. At 30 MPH or so, I get within maybe 20 ft of their cars before they start pulling away from me at the intersection. So in this case going faster means going slower...

[touringcamry]

Here's a topographical map of the area.
http://maps.google.com/?ie=UTF8&ll=3...10428&t=p&z=11

I use 280 whenever possible.

[Buurin]

Interesting, not unlike DWL which I have been doing these days, only more advanced. It also seems like I will have to take up all slacks in my throttle cables and drive barefoot.

I have a DashDyno. Does it count?

[RningOnFumes]

Well, what isn't included in that write up is that while in doing that action, your speed will diminish ever so slightly when you are on flat ground.

And that is why I say you can still try it out without having the use of a SG. It's not exactly coasting and it's not exactly giving gas, it somewhere in between. You're really taking advantage of the lesser load you would put on the engine. You're draining your speed ever so slightly.

So you will have to do this over many tanks to fully realize that perfect setting for it to occur if you don't have an SG. But once you get the feel for it, you won't forget it.

[JustAnotherAsian]

hang-time and dfco user here. oddly enough, i found both techniques on yarisworld before i read more on them on ecomodder and cleanmpg. hang-time was a more recent find in my case.

hang-time is tricky on my '03 camry, mainly because i can't verify without an sg and its tps reading. i'm merely guesstimating my reduced throttle opening and constant rpm.

but you're right. sometimes, i'm wondering if i'm merely decelerating and not really doing anything at all. if i am doing it right, it's decelerating too fast for the long straights imo. accelerating would just blow away that max 10% mpg raise. i think my 4th gear ratio ('03 i4 automatic's overdrive) is too tall for this and the road/load has too much of an effect against hang-time.

there are also not enough straights like the 210 like touringcamry said (especially the IE section).

hence...
i'm shopping for gauges! i'm looking into the ecometer. although the tps and all the jillion other readings that the sgII has isn't included, i assume it's all taken into factor when determining general instant and average mpg, which is the main thing i would look at anyways.

[Tigerotor77W]

I know that I can maintain speed roughly (say, 45 MPH) and see my RPMS drop from 1,800 to around 1,500 (this is in 4th on a 2.4L AT Camry). Is this still the same principle, or, because I'm letting my RPMs drop, is this not "hang-time?" I don't have a Scan Gauge to verify.

[RningOnFumes]

Tiger, I believe you are describing DFCO there. In doing hangtime, you should not see that much of a drop in RPM, if any over a stretch of road.

Let me see... if you are in it, RPM should seem to stay the same, as with the movement- it should feel as if you're not doing anything but keeping your foot there. Here is an analogy, take a 10 speed or 18 speed road bike. The faster you go, the bigger the gear you should be in, right? Well, hang time is as if you are going at the top speed of one gear, but not switching to the next. You're still pedaling but the work load is not as much (if at all) as before when you needed to get up to speed. On the bike, common sense tells you to coast with no leg work, but you keep at it, same rotations, just less work.

[Tigerotor77W]

Interesting. In most gears, I can let off the throttle a little bit -- enough to see the RPMs drop, but not enough for the car to start slowing down. My DFCO is so severe that on a fairly steep downhill, I still won't be able to gain speed (but rather only maintain speed or even slow down).

There's too many hills around here to give it a shot, but when I get back to IL I'll give it another whirl. Thanks for the reply and analogy!

[Bitter]

Originally Posted by Tigerotor77W

I know that I can maintain speed roughly (say, 45 MPH) and see my RPMS drop from 1,800 to around 1,500 (this is in 4th on a 2.4L AT Camry). Is this still the same principle, or, because I'm letting my RPMs drop, is this not "hang-time?" I don't have a Scan Gauge to verify.

sounds more like the torque converter clutch went into lockup.


i'll assume this is only for cars with drive by wire and not throttle cables?