Squeezing extra MPG out of P&G (EOC WHILE KEEPING THE CAR ON??)

[jedi_sol]

Ever since I took my car into the dealership to service, I disconnected my kill switch, so I have just been doing regular ENGINE ON P&G this whole week. I noticed something interesting.

This might not apply to all cars, but on my 2013 Subaru WRX Sti, I notice then when I shift to neutral to ENGINE ON coasting, my ScangaugeII indicates 9999mpg for a half second when rpms reach approx. 900rpm.
Does this mean my injectors are actually turning off for that half second around 900rpm? I busted out my Torque App and drove to my regular “testing grounds” to verify.

Testing grounds – 1 mile stretch of road with a slight incline, late at night, in a business park so no traffic to disturb

I setup the Torque App to read FUEL USAGE to the 1000th decimal point, because I know fuel usage for 1 mile neutral coast would be minimal, but this is simply for testing purposes.

I drove up to 40mph, shifted to neutral to initiate coasting , set the app to start reading fuel usage until a pre designated ending point. I did bi directional runs

Straight engine on coasting
.018
.015
.016
.015
AVERAGE - .016 fuel used

Engine on coasting, blipping the throttle to allow rpms to sweep 1000rpms down to 900rpms
.014
.014
.014
.014
AVERAGE - .014 fuel used

Straight engine on coasting
.015
.015
AVERAGE - .015 fuel used

Total fuel used with STRAIGHT ENGINE ON COASTING IN NEUTRAL - .0156
Total fuel used with ENGINE ONE COASTING IN NEUTRAL WHILE BLIPPING THE THROTTLE – .014

That’s a potential extra 10.26% savings in fuel WHILE USING A FUEL SAVING TECHNIQUE!

I’m thinking of the potential benefits for ecomodders
1) Achieve “simulated” EOC while keeping the engine on means you keep power steering on, you keep full braking power, you keep your ac running.
2) Less wear on clutch on transmission if you no longer need to bump start

On this morning’s commute to work, there is a long downhill I normally coast in neutral, typically scangauge II reads 150-200mpg during the whole coast down, I blipped the throttle more rapidly to stay in the 900rpm sweet spot and my scangauge II indicated 9999mpg on the whole way down.

I’ll do more testing and post up my Torque App readings later!

[bikenfool]

It could be. But keep in mind that scangage & torque don't actually measure fuel consumption, they estimate it. They probably use mass air flow & O2 sensor.

[elhigh]

That doesn't make sense. I think you've found one of the many places where the real world and the technological world aren't quite in the same plane. I suspect - and I'm going to subscribe to this thread because I really want to know more - that when you fill up it will turn out you've actually used more fuel.

If you haven't, well, I got nothin'. That would be me with a big heapin helpin of egg on my face.

[vskid3]

Originally Posted by bikenfool

It could be. But keep in mind that scangage & torque don't actually measure fuel consumption, they estimate it. They probably use mass air flow & O2 sensor.

I suspect it has something to do with the refresh rate and how the fuel usage is calculated by the scanners. I don't think I would trust anything other than an MPGuino in this testing scenario.

Was the car fully warmed up for the first A sets? I would suggest doing another B set after the second A to try to rule that out (so ABAB). Your sets are all extremely close, with your second A being right in the middle of the first A and your B. Looks too close to call it, in my mind, especially without being sure the instrumentation is inaccurate in this situation.

[jedi_sol]

I've still got my old mpguino , I'll hook it up and see.

I'll post my findings soon!

[bestclimb]

my subaru does the same thing. I think it is actually using zero fuel for an instant as your foot comes off the gas it goes into open loop. which means it is disregarding the O2 sensor and fueling according to the fuel maps. at some rpm >~1000 and off the throttle it goes into DFCO.

am looking forward to confirmation or correction on this.

[jedi_sol]

Originally Posted by bestclimb

my subaru does the same thing. I think it is actually using zero fuel for an instant as your foot comes off the gas it goes into open loop. which means it is disregarding the O2 sensor and fueling according to the fuel maps. at some rpm >~1000 and off the throttle it goes into DFCO.

am looking forward to confirmation or correction on this.

good, so im not crazy then!

I'm trying to find the floppy disk drive cable that came with my old mpguino, then i'll hook it up this week.

I'll also grab my volt meter and hook it up to the injectors as well to see if the signal goes to 0 during that ~1000rpm range.

[bikenfool]

Actually this might make a lot of sense. Perhaps its going into DFC for a bit. It could be more efficient to pulse the engine, blips, instead of just idling.

[jedi_sol]

Originally Posted by bikenfool

Actually this might make a lot of sense. Perhaps its going into DFC for a bit. It could be more efficient to pulse the engine, blips, instead of just idling.

EXACTLY ...this is what I am experimenting!

The potential is that i can get the same effect as EOC while keeping the engine on...thus less wear on clutch due to no more need to bump starting, you get to keep power steering on, you get to keep full braking power on, you get to keep air conditioning on, no need to hack wires to install a kill switch.

My girlfriend approves this technique, she says
"as long as you dont have to kill switch the car, its ok with me..."

[bestclimb]

Originally Posted by bikenfool

Actually this might make a lot of sense. Perhaps its going into DFC for a bit. It could be more efficient to pulse the engine, blips, instead of just idling.

I think this has been tested (though not necessarily for a subaru with it's added AWD drag), leaving it in gear pulsing then coasting down in gear with dfco. from what I remember the coast downs were short enough that coasting in neutral with the engine idling was more efficient.

The wear from a bump start is pretty negligible given the forces involved. With a bump start you are getting the weight and drag of the moving parts of the engine going. Compared to just getting the car moving you are getting the whole mass of the vehicle moving.