Engine braking without using fuel idea

[hyperyaris]

Many modern cars including my Yaris already come with DFCO. Does yours?

[max_frontal_area]

Bosch VE pumps (and japanese versions), except for those fitted in cummins engines are lubricated by fuel, yeah as if ULSD will lubricate ;~> same with the stanadyne pumps if you run them in hydraulic braking mode with the fuel shut off you can harm or destoy these already fragile IPs.
the inline Bosch pumps especially the 5 cylinder version automatically shuts of fuel on downhills...

[hyperyaris]

Make sure yours does not already use a form of DFCO and save yourself grief. A Scanguage will read 9999 mpg in DFCO mode.

[MetroMPG]

Originally Posted by The Atomic Ass

Not necessarily, my father's Bravada will cut if I shift down to 2, and EB down a hill at 25-30 mph. I do not know if it's locking the converter or not, though.

See disclaimer about my general lack of familiarity with automatics.

Maybe there's enough pressure in the unlocked torque converter to keep the engine turning in some cars. I wouldn't be surprised.

[MetroMPG]

Originally Posted by The Atomic Ass

Not necessarily, my father's Bravada will cut if I shift down to 2, and EB down a hill at 25-30 mph. I do not know if it's locking the converter or not, though.

See disclaimer about my general lack of familiarity with automatics.

Maybe there's enough pressure in an unlocked torque converter to keep the engine turning. I wouldn't be surprised.

[RH77]

Originally Posted by hyperyaris

Make sure yours does not already use a form of DFCO and save yourself grief. A Scanguage will read 9999 mpg in DFCO mode.

I've found that this isn't always the case.

From the Integra shop manual:

"During deceleration with the throttle valve closed, current to the fuel injectors is cut off to improve fuel economy at speeds over following rpm..."

Basically standard engines are 950 rpm U.S. and 1050 rpm Canada.

...but I don't get the 9999 mpg indicator (and never have in tons of rental cars). So anyway, I often downshift on exit ramps or up to lights if I have to stop unexpectedly.

You can generally see and feel the transmission/TC give a bump in revs right below the cutoff.

Modern fuel injection probably has it -- at least OBD-II, maybe earlier...

RH77

[UK Mini]

You don't need a solenoid for the fuel pump, it turns itself off when it senses the pressure increase from the closed carb float valve. Fuel flows into the engine because air pressure across the carb venturi is lower than that in the float chamber, to stop the fuel you just need to equalise the air pressure. SU did this themselves by connecting the float chamber vents to manifold vacuum and atmosphere. By closing off the atmospheric vent with a solenoid valve full manifold vacuum was communicated to the float chamber. Pulsing the valve stopped fuel being drawn up the vent pipes

[PaleMelanesian]

I watch the Loop gauge on the Scangauge. It goes to Open Loop when it's in DFCO mode. There's no need to monitor the exhaust O2 levels if you're not injecting any fuel, right?

On both my Hondas, it holds DFCO down to about 1200 rpm, then fires the injectors back up. My civic is a manual, but the 04 Odyssey is an automatic. As long as I downshift to keep the rpm above 1200, I get DFCO.

That said, it's almost always more efficient to idle the engine and coast in neutral - momentum is more valuable than the light fuel usage.

[bgd73]

cutting fuel to a carb(s) may change bowl level. It may not throttle right away back into power...
just a thought.
I run carb too. if to add air bypass for a carbed system, engaging when throttle is off, that works good. I have yet to get a way for it to work on the carb system,
An idea is an egr not used that is a valved source into intake. maybe convert it to electric like fuel injected, and be it from a filtered line using the air intake filtered. Long engine braking on a carbed engine and no air bypass, can pump vapors into intake from the base (hence carbed engines stay clean for 50 years versus an air bypassed one that pigs itself all the time).

so there is drawbacks in any direction.A truck's jake needs no vacuum, they smack the valves around..so there goes ideas of "vtec" as a jake..vtec sucks at anything really, but that is not the subject here.
one could add a bigger vacuum canister, but on little engines, it will be a rough idle until satisfied.
manual brakes and manual sterring retirning to the primitives of man and machine would save the world. But we cannot have that either can we?