Injector fuel cut off

[wagonman76]

My Celeb does DFCO quite a bit on long downhills. My 6000 almost never does it, its done it only about 3 times all winter. My 92 Trans Sport with 3800 never does it. One thing I would like to try sometime is an injector cutoff momentary switch, then open the throttle while cutting fuel to hopefully keep the engine from slowing down as much.

[ECONORAM]

My 90 Audi 100 AND my 91 VW Jetta would both perform a decel fuel cut-off. The Audi was an auto, and the VW was a 5sp. The engine kept turning. I just learned about 2 weeks ago that my wife's 08 Dodge Avenger will also do a decel fuel cut-off. See pic.

[bhazard]

As long as the engine is connected to the wheels (through the clutch/torque converter) it will stay spinning. Just cause its spinning doesnt mean it has to be injecting fuel. Both my 88 tbird and 93 festiva cut down to 2000. I wish it went lower. I spoke with a guy that burns chips for the b6t ecu in my festiva, asking if he could drop the cutoff rpm, but he said the codes too complicated, he basically changes the fuelmap and rev limit.

[mwebb]

blue is injector signal
in the image above
in the upper left is the screen this image was culled from , note the gap in the blue trace .
that gap is DFCO , there was no injector signal from the ECM during the gap .

i captured this by snapping the throttle to WOT then releasing it , allowing the engine to slow down from the speed it reached during the WOT snap , as soon as the TPS shows closed throttle and rpm is hi
the ECM shuts off fuel , the ECM starts fuel back up when it sees rpm falling below the value it was programmed to restart fuel at .

all newer cars have DFCO .

if your car does not Have functioning DFCO , the first thing to check is the TPS or closed throttle switch , because if the ECM does not know the throttle is closed , it will not activate DFCO

[comptiger5000]

I think my TPS is flaky then, as my Jeep will go into DFCO when it feels like it, or sometimes bounce in and out randomly. I have yet to find a definite cause, however. I'll pop in a new TPS and see what happens.

[texanidiot25]

Originally Posted by 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.

Mind showing me the wiring or where you read this? Out of curiosity.

I know they had a few places in the 3bbl (really, 2 and 1/10th lol) where the archiac ecu could limit fuel, but not shut it off entirely.

I do know, however, if you EOC with the throttle wide open... You can get some nice fireworks out the tail pipe. Nice to use on occasion, though not good for the motor..

[EdKiefer]

here info for gen8 08+ accord 2.4L from Honda service fuel/ECU doc .
relating to fuel cut off .

"Fuel Cutoff Control
During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at engine speeds over 850 rpm (A/T) or 1,000 rpm (M/T). Fuel
cutoff also occurs when the engine speed exceeds 7,000 rpm (LX) or 7,300 rpm (EX), regardless of the position of the throttle valve, to protect the engine from over-revving.
When the vehicle is stopped, the ECM/PCM cuts the fuel at engine speeds over 5,000 rpm (A/T), 7,000 rpm (LX M/T), or 7,100 rpm (EX M/T). The engine speed of fuel cut "

On my LX accord you can feel injectors shutting down, as you can see they have the turn on very close to idle speed .

[some_other_dave]

I read in one of the 1990 CRX manuals (either owner's manual or workshop manual, I don't remember which) that the CRX shuts off the injectors when the throttle is closed and the RPMs are above 2500. I am pretty certain that I read it in one of the manuals, but I have looked for the info again and have not found it.

But yes, as others have said--when you're coasting in gear, the turning drive wheels are causing the engine to turn, so cutting off fuel doesn't kill the engine. You might be able to kill it if you enter DFCO and push the clutch in, but it's also possible that the ECU will see the clutch action and start the injectors again, or that starting them up again at whatever the lower RPM bound is will get the engine running on its own.

I have heard rumors that the earlier carbureted Civics would also shut down fuel flow on overrun (coasting with throttle closed, very very high manifold vacuum), but haven't seen any documentation of it. It would be cool to have a reference for that. Those Honda automotive carbs are hideously complex things; it wouldn't surprise me at all if they have provisions for that.

-soD

[texanidiot25]

Hideously complex, but when working properly one of the most trouble free carburetor setups ever, because it tries so hard to mimic fuel injection. To start my '87 CRX it's just one pump of the pedal to tell the carb to choke and fast idle, and just turn the key. It can even adjust the fuel ratio to some extent, with an 02 sensor... if it wasn't a California model like mine -sigh-

All hell breaks loose when vacuum lines fall apart and obsolete "computers" start to malfunction, however.

[texanidiot25]

Hideously complex, but when working properly one of the most trouble free carburetor setups ever, because it tries so hard to mimic fuel injection. To start my '87 CRX it's just one pump of the pedal to tell the carb to choke and fast idle, and just turn the key. It can even adjust the fuel ratio to some extent, with an 02 sensor... if it wasn't a California model like mine -sigh-

All hell breaks loose when vacuum lines fall apart and obsolete "computers" start to malfunction, however.