Hang Time: Exploiting ECU Fuel Maps for Fuel Efficiency

[BailOut]

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.