MPG under engine break

[lazibayer]

My ride is 2015 GT PP and its MPG looks awful under engine break. There is a 1000ft downhill slope from my home to work place, and the MPG reads ~13 when the car goes downhill at 30MPH in 2nd gear. The slope is so steep that I have to hit the brake to hold the speed. 3rd gear gives ~25 MPG and 4th gives ~30. I did the same thing to a 2015 Forester XT and it shows a full bar of MPG when I do engine brake with fake CVT gears. I thought modern cars will always cut fuel injection under engine brake so MPG will reach the up-limit of the gauge.
In daily driving, the MPG gauge of the 'stang does sometimes climb to 40 under engine brake in 2nd ~ 4th gears, even on some flat roads, but I couldn't figure out the pattern. I used to drive a Kizashi and the Forester in the same city and their MPG gauges almost always hit the ceiling when I did engine brake.

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[Billy1]

How many miles do you have on the car? Also, you didn't buy it to get good gas mileage did you?

Figure on getting 15-17 mpg. in town.

 

[fionic]

My ride is 2015 GT PP and its MPG looks awful under engine break. There is a 1000ft downhill slope from my home to work place, and the MPG reads ~13 when the car goes downhill at 30MPH in 2nd gear. The slope is so steep that I have to hit the brake to hold the speed. 3rd gear gives ~25 MPG and 4th gives ~30. I did the same thing to a 2015 Forester XT and it shows a full bar of MPG when I do engine brake with fake CVT gears. I thought modern cars will always cut fuel injection under engine brake so MPG will reach the up-limit of the gauge.
In daily driving, the MPG gauge of the 'stang does sometimes climb to 40 under engine brake in 2nd ~ 4th gears, even on some flat roads, but I couldn't figure out the pattern. I used to drive a Kizashi and the Forester in the same city and their MPG gauges almost always hit the ceiling when I did engine brake.

1. the gauges aren't always accurate
2. no throttle decel = no fuel

 

[jasonstang]

I am breaking in my automatic and I get full bar 40 when going down hill.

 

[Higgs Boson]

In order to get Deceleration Fuel Cutoff active, you need to take the RPM over 1700 and then let off without touching the gas pedal at all. It will stay active until 1000 RPM on the way back down. So if you are going slow and cruising at 1500 RPM and let off, it will not work.

 

[BBB]

My v8 is a gas guzzler

shocking

 

[lazibayer]

In order to get Deceleration Fuel Cutoff active, you need to take the RPM over 1700 and then let off without touching the gas pedal at all. It will stay active until 1000 RPM on the way back down. So if you are going slow and cruising at 1500 RPM and let off, it will not work.

Thanks for the info. The RPM is around 3000 at 30MPH in 2nd gear. No I wasn't touching the gas pedal at all.

 

[lazibayer]

How many miles do you have on the car? Also, you didn't buy it to get good gas mileage did you?

Figure on getting 15-17 mpg. in town.

I am getting 13~14 locally and I don't mind it at all. I like the engine/exhaust sound above 4k rpm and I am willing to give some gas for that.
But I do want my good gas burnt for a good reason. If Deceleration Fuel Cutoff impedes performance then let the gas flow.
The car has a little over 1000 miles on it.

 

[Tninl16]

Check the Air/fuel ratio on the gauges readout. Mine usually pegs at 20.0 when i am off the gas in my auto.

 

[Higgs Boson]

Thanks for the info. The RPM is around 3000 at 30MPH in 3rd gear. No I wasn't touching the gas pedal at all.

if you are running up to 3000 RPM and expecting good mileage you might be disappointed....

 

[Starman]

12.5 MPG and Im almost at 1K miles now. I dont feel like Ive beaten it all that much. 92 gas.

 

[lazibayer]

Just to clarify when I mentioned "MPG" I meant instant MPG.

 

[Quesever]

I don't think most here are getting what's being asked. No one expects a V8 to get good MPG at 3k RPM, but getting ~13 MPG while coasting downhill, even if the tach is at 3k seems a little off.

 

[jasonstang]

if you are running up to 3000 RPM and expecting good mileage you might be disappointed....

Not necessary.
Engines actually run more efficiently at mid range rpm than lower rpm. You spend more time at lower rpm where mid range rpm will accelerate you faster.
Avoid braking and follow the flow of traffic gets you better gas millage than short shifting.
He was going down hill using engine braking so it could be 6000rpm and the injectors should not inject any gas.

 

[MattBassAce]

I was averaging about 17mpg per tank my first 2-3k miles. Now im averaging 20-21 mpg per tank and have 9kmiles on the car. I didnt change my driving habits and still have the same 20mi commute to work. Engine breaking mpg is good. And i have the PP.

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