p&g engine on manual transmission

[Hersbird]

Well I got a obd2 Bluetooth and the torque pro app for my 2002 Subaru Forester and have started trying different techniques. I have a short 3.5 mile commute that has 7 stoplights, mostly a 35 mph speed limit with a bit of 45, and takes me about 10 minutes, and mostly busy traffic. Over the last 5 trips I have averaged 23mpg according to the guage with a worst of 20 and a best of 25 for a single trip (actually off rush hour on an extra trip I got a 30 but caught every light, so not counting that) using a mild p&g keeping the engine on just pushing in the clutch for a glide. I end up keeping up with traffic as I only drop about 5 mph at a time and then make up the gap. It seems to do better then just keeping steady and then coasting if a light goes red. The gauge says it only uses .3 gph at idle and actually for a few secs of the coast it reads 0 gph. I usually can't use 5th gear unless that 45 mph sec is moving well and I just sort of 1/2 throttle the pulse in 4th most of the time. I'm going to try some more steady driving for a few days next week but doing things the old way I usually only got 200 miles with a 10 gallon fill. If the gauge is right and I can get 23-25 constantly it seems worth it. I still have the studded tires on and have done no mods to the car.

[jedi_sol]

welcome fellow Subaru Owner!

Yes, p&g is typically more efficient than steady state cruising. The only time where it does not help is if the "glide" portion is too short.

Originally Posted by Hersbird

The gauge says it only uses .3 gph at idle and actually for a few secs of the coast it reads 0 gph.

Very astute observation. I've noticed my 2013 wrx Sti does the same thing and I think I have found a way to exploit this. I've done some experimenting.

http://ecomodder.com/forum/showthrea...ile-28507.html

It appears that when you step off the throttle, the ecu cuts fuel to the fuel injectors. Therefore, while I am "gliding" during the p&g, if I gently tap the throttle, the ecu will think "off throttle...cut fuel....off throttle...cut fuel...off throttle cut fuel," therefore, I can essentially coast while using very very very minimal gas. My testing shows that I use approximately 78% less gas by "blipping" the throttle vs. straight neutral coasting.

You should try this technique and see if your torque app shows any improvement in mpg during your p&g.

[Hersbird]

I was reading your thread before an didn't understand how it could cut all fuel and still run but now I think I see. The engine is still falling from about 2500 rpm and there is probably still some residual fuel it is using. To me this seems like a short little glide following a short little pulse would take advantage of this w/o having to shut off the motor. Still it seems like my glides are 2-3 times longer then my pulse.
I also was thinking this would really pay off on my old Barracuda, with no overdrive and 3.23 gears with 25" tall tires it really turns some rpm on the highway. Sadly I sold it last year to pay off some debt. The guy that bought it drove it 2000 miles home and said he got about 17. Not bad for a 350hp 360 but I bet with P&G it would have been much better.

[jedi_sol]

yes, from my observations, it appears the "fuel cut off" is mainly related coasting in neutral with throttle input. I did not see any relation to rpm. For testing purposes, I blipped the throttle coasting in neutral at around 2500rpm vs 900rpm...it made no difference.

Keep in mind, this method is not a "short pulse/short glide/short pulse/short glide"

It is Pulse...then glide.....while you are gliding gently tap the throttle.

Engine off coasting will get you the most mpg. P&g is the next best option. The advantage to my technique is that you can essentially pulse and glide while practically simulating engine off coasting during the "GLIDE" portion.

Other benefits, you get to keep the engine on, you keep power steering, you keep full braking power, and you get to keep a/c running.

[MetroMPG]

Just a thought: keep in mind the zero fuel use you're observing when releasing the throttle while in neutral might be a function of the OBD-II gauge. (They don't directly monitor fuel consumption -- they monitor air consumption and estimate fuel use based on an algorithms. EG: the Scangauge's "fuel cutoff" threshold which reports zero-fuel use is actually user-adjustable.)

The surest way to confirm what you're seeing is actually happening is to directly monitor a fuel injector.

[Hersbird]

I was beginning to question this as I shut the car off at a light yesterday and it continued to read .3 gph for 15-20 seconds after shutting the car off.

[jedi_sol]

I'm getting closer to proving my theory

Here is the video. Mpguino has not been calibrated yet, this is just to simply show that the fuel injectors cut off when I step off the throttle.

Fuel injector cut off with pulse and glide: Fuel injector cut off with pulse and glide - YouTube

yes ultimately the reason I decided to move away from torque app was that it still shows fuel flow even when the car is off. that is why I only give it 3 stars on Google Play review