Injector fuel cut off

[trikkonceptz]

It is a term I hear thrown around here many times in many different threads. Has anyone ever proven this using a fuel pressure gauge? Or confirming that the voltage going to the injectors is Zero during these moments?

Using a scangauge is inaccurate especially if you think the 9999mpg's means you have no fuel running, unless you have precisely calibrated the scangauge to do so ...

I just feel if your vehicle does shut off the fuel the engine would stop completely, ala shut down, requiring a restart by bump start or in auto's turning the key again.

Can engines reduce fuel flow during certain conditions, yes ... do they shut down, no, unless they are a hybrid in which case you would feel your engine shut down and restart as hybrids do ...

Please clarify this as it bothers me to hear some say that their 1984 crx has a fuel cutoff when coasting ... (that statement was random BTW)

Thanks ..

[Bearleener]

I measured the injector pulse width with a multimeter's duty cycle setting and yes, the injector shut off completely. Unfortunately on my car that only happens above about 1700-1800 rpm, i.e. it only helps on the highway. Most more modern cars do this down to a considerably lower speed. It could be that some cars add a tiny bit of fuel, possibly because at lower engine speeds it might otherwise jerk a bit when you add gas again. I'm pretty sure that a mid '80's car would already have fuel cutoff. The Golf II did (1983-1992).

I suspect that in city driving it doesn't make sense to downshift when approaching a stoplight just to activate fuel cutoff. In almost all cases it's better to let 'er roll in neutral, i.e. anticipate the light when possible.

[Nevyn]

Search around for DFCO - that's the common abbreviation for "Deceleration Fuel Cut-Off." My 93 Lumina does it. Drop it from 4 to 3 when warm and headed down hill, and you can feel the car slow down more than just the gear change. It's as if someone grabs the rear bumper and is holding on the car. My MPGuino also shows it - the instantaneous gallons per hour drops to zero. The engine is still turning, but it sounds funny - has a weird "woosh" sound to it. It keeps engine vacuum, so I never lose power brakes, but there is definitely no fuel. When I kick it back to 4, the tach drops like a stone to about 200 and then you can hear/feel the "vroom" as it turns fuel back on.

[mobilerik]

hmm... I never made the connection... Can the "injector cut hack" be made to work like DFCO, so that you don't have to key-on again?

btw, the ScanGauge "cut-off" setting is based on returning the throttle to the starting position (or below a position you specify), but it doesn't have a way to specify if it only stays in cut-off mode above a certain rpm. In my case it's above 1500rpm, and I find it pretty useless unless I would otherwise be braking at highway speed, which is hardly ever.

[Ryland]

According to the wiring diagram the 1984 crx's do cut fuel while coasting in gear, and as best as I can can tell all 3 barrel carburator civics did this.

[trikkonceptz]

So then this is a function of the ECU ...

Whereas it cuts power to the injector, thus no fuel.
It then has to cut power to the electric fuel pump or no?
Then since the engine is still turning, you still have steering etc.
The valves are still moving also, which means once you give it gas it has to be timed to the correct cycle in order to get combustion again.

All within mili seconds .... impressive

Now on cars that can do this how long can you remain in this state? I'm guessing it is determined by rpm?

I also assume like it was said earlier that the coasting effect is reduced more than coasting in neutral so is it practical and what is its ideal use ...

[dcb]

I've watched the injectors shut off using a mpguino, I forget where I posted the figures but on a metro the DFCO did not kick in unless you start coasting in gear at like over 40mph and stopped at about 25mph or so.

The fuel pump operation is independent of DFCO

[Ryland]

On all of my Hondas the fuel pump always runs as long as the key is turned on, the fuel pressure regulator bleeds fuel back to the fuel tank from the fuel rail, keeping the fuel rail at a steady pressure, the injectors are just valves with fancy little nozzles on them and they are controlled by the cranks shaft positions sensor, and the ECU, so all those parts are still working the ECU is just not telling the injectors to open at all, it's really very simple, it's just a single part of the chain that is being opened.
on early civics the carburator is being told by the ECU to close about 5 valves and that cuts off fuel to the engine, again no fancy timing is needed to restart, it just opens the valves (part of why you have those vacuum lines), it also prevents the engine from over heating and becoming damaged puts less stress on everything as it's not trying to produce power while it's slowing down and it's not trying to burn a fuel ratio that is something other then 17:1.

[Formula413]

I have a '97 Escort and as far as I can tell I don't have DFCO, no idea why though. I can watch injector pulse width on the SGII and it never goes to 0, even when engine braking.

[taco]

i can feel it on all my cars/trucks

the camry i can feel it as a drag once warm and i left off the gas. it kicks back in at abou 1100rpm, and u can feel the car coast easier.

i was coming down the 4 lane, and left off the gas sg hit 9999 for over 10miles(all down hill). my wife looked over and said i think u broke it.

my white truck is abou 1200-1300 rpm
grey truck is abou thte same.