Am I on to something?

[zjrog]

Interesting... Hang time, will have to try it.

[AeroModder]

Here's the post over on CleanMPG:

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.

This says you need instrumentation for it, but I've been going by feel and ear. Except with non variable-valve-timing engines, there are mixed results as to whether this works or not. But after using this technique with two passes at a drag strip and some fast freeway driving, and still rubbing up against my best tank, I think it can still work for non-VVT/VTEC cars.

[MetroMPG]

Madison: FYI, it's not pulse and glide if there's no glide. Glide = transmission in neutral.

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My bet is you simply drove more conservatively overall due to the open pipe, and your improved fuel economy isn't simply from this one tactic.

Personally, I've tried "pulse and bleed" several times in my own non-lean burn, non-hybrid, non-vvt car, and found no benefit over simply driving with load (DWL).

[wagonman76]

Here's the post over on CleanMPG:...............

Sounds just like what I do a lot.

[rmay635703]

Originally Posted by MetroMPG

My bet is you simply drove more conservatively overall due to the open pipe, and your improved fuel economy isn't simply from this one tactic.

This is the method I use on my Buick to net almost 40mpg, its very odd and seems to only occur on automatic vehicles, MT it doesn't happen.

Its reverse of DWL in that you allow the car to slow (very slightly) on flat or inclines and for me was much more effective than DWL. I also would accellerate when needed on flat ground or down inclines if needed and still DWL'd as much as I could up the incline but needless to say on an auto you can't DWL up long hills the whole way.

My foot would get tired because the motions were so small, but I could maintain speed barely for tremendous distances while getting about 10mpg better FE on the guage

Something to try on an auto I guess. It doesn't really work on my dodge because the thing slows down like it has a parachute behind it.

[AeroModder]

I wish I could get the tranny to stay in high gear at lower speeds, but since it's an auto, it won't. I guess this could be a trick to get automatics to give better mileage!

I need to pick up a scangauge or something so I can actually quantify this.

[MetroMPG]

...MPGuino. ScanGauge won't work in pre-ODB-II vehicles.

[99LeCouch]

Interesting. I must be bleeding speed too quickly. I'll have to try this on my next long trip.

[gascort]

Aeromodder, you may have the same circuitry in your car as my escort has. (with lean burn)... I've only found a thing or two on the internet about it; apparently Ford called it LOC (Lean On Cruise).
Mpguino and others' wide band O2s have verified this; when the car's warm and in closed loop for a few seconds at light throttle and at speed, it re-enters open loop and increases AFR (air to fuel ratio) up to around 17:1 (If I remember correctly).
If I watch my iMPG on my MPGuino on a flat stretch while going 60-ish mph, I see numbers go between high 30s and mid 50s when this switches on and off.

My goal is to get the car aero and low engine drag enough to do this part time thing at 65-70 mph and all the time at 55-60 mph - would let me get into the 50s.

[gascort]

The Yeager's Ford Escort LX Wagon
March 2005 post

Ford Escort Owners Association

There's also an EPA bulletin mentioned about emissions and the escort's lean burn, but it's been taken offline since it was linked anywhere. I have all the emissions sniff test results; the car always performed way below regulations!

Apparently it's not a new thing; there's mention online of it being on GMs around the 90s