MT and DFCO

Any tuners have insight into why Toyota did not implement deceleration fuel cutoff on the manual transmissions?

I just tested again and found gal/hr to be significantly higher when decelerating in gear than when decelerating in neutral

 

I am no mechanic or engineer, but wouldn't it make sense that the fuel rate would need to be increased to sustain the higher RPM's?

 

My ‘21 had DFCO like normal when decelerating in gear.

 

97% sure it happens when you’re in gear and off the throttle. Like when you would think to roll down a hill in neutral, you’re actually better off rolling in gear.

@tonered?

 

I prefer REVCO when accelerating

 

When monitoring the pids fuel rate was much higher when decelerating in gear than when decelerating in neutral.

Idle = ~.3gal/hr
Decel clutch depressed/neutral = ~.3gal/hr
Decel 55mph 6th gear = ~.8gal/hr
Decel 45mph 2nd gear = ~1.25gal/hr
(2nd gear to test higher decel load)

 

When you say decelerating, are you engine braking or pedal braking?

 

No brake pedal. All engine

 

beats me then. Maybe somebody else will know more...

 

It does, but oddly what @Firn observed is real. The higher the revs in DFCO, the higher the fuel flow rate.

I asked vF Tuner about it a few times, but never got an answer. I even proved it to myself on a long 6%+ grade. Coasting in gear didn't do much for the Trip MPGs. Coasting in Neutral really bumped them up.

That said, I do like the effect of DFCO.

 

Further though, @MOC221_ did prove that even shutting off the ignition did not change the level of engine braking. So, I have no real idea WTF is really happening.

 

If you guys don’t know, then that’s good enough for me

 

Cheers!

But, I wanna know.

 

funny i was wondering the same thing yesterday. i dont know much about mechanics but i have watched the mpg closely in my MT and i think sometimes it lies. for example sitting at a stoplight it says im not burning any fuel. or coasting in neutral. could it be that its just programmed to display fuel usage in an unconventional way? regarding decelerating in gear i will try and measure as well. but my guess is that the mpg display is just incorrect.

 

It sounds like you are looking at Gal/Min? Switch that to Gal/Hr. You should see just under 0.2gal/hr at idle when the A/C compressor is off.

 

Thinking about this more…wonder if the truck is smart enough to account for deceleration vs acceleration (or at least less deceleration) when coasting on that 6% hill…. You figure you’re engine braking and probably slowing in gear with or without fuel but probably picking up speed in neutral. Might use less fuel in DFCO for that short time but then to get back up to speed you’ll burn it right up again? Kinda doubt it’d account for that, but something’s out of whack

 

kk ty

 

So what sensor does the truck use to measure fuel flow?

 

It looks to be a standard obd pid and should be calculated simply from the ECU running the engine. I expect it's as simple as injector duty cycle and fuel pressure but I could be that and more.

 

I would like it if it was that smart, but I do know that in our other MTs, DFCO MPG increases were quite visible.

Of course, it could just be some internal error?