Say you are coasting down a hill, and the engine is being pushed to high RPM's, how much gas is it using? I can't imagine it isn't using any, but I can't imagine it's using as much as if you were revving it with the pedal. What goes on with the fuel delivery system? Does anybody know? TIA.
Dan

Yeah I know, I'm kind of ignorant...

 

ignorance is only an excuse once.

in most PGM-FI Hondas, when the ECU (the engine computer) senses that the throttle is closed through the input of the throttle position sensor (TPS) it shuts the injectors off.

this is really good for fuel economy...

so when you are coasting down hill, with foot off the peddle, it doenst use any gas...

there you go

t..

 

it must use some gas, how would it idle???

 

The injectors are switched back on when the rpm goes below 1000 or around that point.

 

If you had an air/fuel gauge you'd know that it does indeed shut off the injectors... goes to full lean

 

So then when the idle goes below 1000 or you get on the gas, it basically roll-starts the system again?

 

i've always wondered this too. i figured it must cut down the fuel but its really interesting to know that it shuts it off completely. good question!

 

Yes, the air/fuel jumps back to stoich when you press the gas. Kinda fun to watch

 

Going to full lean cannot be good for the car. Especially at high RPM's.. I guess I don't understand Honda's thinking.. The whole "fuel cutoff" and shutting down injectors, especially when the engine is at high rpms.. I just don't get it I guess.

 

I don't follow you... if there's no gas going in, it's hardly 'going lean'... it's just plain not running.

 

The injectors may be off, but the thottle body is closed too. It dosn't really go lean

 

Very true points made by most. Dont be liek some people and keep upshifting to a save fuel while they still apply hard throttle pressure. Ive seen people mat the gas in 5th and cruise at a steadily climbing 30 - 50. When the gas is floored te TB is open and your car is sending fuel like no tommorrow to pull it out of the lagging stage. Apply soft accelerator pressure and just coast in 4th or 5th if needed.

 

bull! half this thread is crap!

If the PGM-FI ECU receives a closed throttle input (under 0.5V), the engine speed is above 1100 RPM, and the engine is warmed, the fuel injectors will be shut off.

it is that simple.

there will be NO fuel. that is Hondas reasoning.

you cannot detonate a mixture of no air and nothing.

t..

 

Ah... I see.. Thank you.

 

Quite zen! "What is the sound of nothing detonating?"

Anyway, I recently went down a long, gradual hill at closed throttle. The engine did indeed cool down a couple of ticks from its normal operating temperature.