fuel cut off for engine braking
- Thread starter NO_SPRK
- Start date
FordGuy100
Registered User
My 6.0 does exactly this when it is in overdrive with a torque converter locked. Love the sound of it, err...lack of sound of an engine rotating with no fuel ignition. Even OBS powerstrokes do this.
I also thought that when engine braking the IP wasn't pushing fuel. I guess the one way to get a rough idea is to listen while doing it, then do it again except turn the key off for a second and see if these sound the same.
justinray
Contributor
The fuel would still be present in the IP, just not going to the injectors
'94IDITurbo7.3
HAMMER DOWN!
the way i see it is, if you need something other than service brakes and grabbing a lower gear then you have a couple things that are going on.....
you are over loaded for the tow vehicle.....
your service brakes need to be overhauled...
your going WAY faster than you should be for the road you are traveling on and the load you are carrying.
you are over loaded for the tow vehicle.....
your service brakes need to be overhauled...
your going WAY faster than you should be for the road you are traveling on and the load you are carrying.
When your coasting/brakeing, there is very little fueling to the engine. Why anyone would want to shut off the fuel to the IP is beyond me. What if the engine wouldn't start again? Dangerous. Besides, the engine is already brakeing the most it can.
That covers it.
NO_SPRK
User & Abuser
its not about over loading or going too fast or worn brakes. it was just a question. ive been working on a idi 4spd truck that lost fuel from issues in selector valve. i noticed how the engine with no fuel is a great brake.
icanfixall
Official GMM hand model
Doing this with a standard trans momentary is not going to hurt anything. Now just make sure the switch is a push to activate and when you let go of it the switch automatically goes back to the normal run mode position. Just like a glow plug manual switch. It only works when you push it. As posted alrady. Its probably illegal in all states. Its not going to harm anything in the pump or injecters. One more thought. I'm not seeing how this is going to give you any engine braking. Now if you were to install a guiteen valve over the intake manifold inlet then you will cause the engine braking your looking for when the engine becomes a compresser that can't suck in any air. Same thing a gas engine does when the butterflys go closed on the carb engines.
jaluhn83
Full Access Member
Several things here:
To clarify, I'm assuming you have a manual trans and you're leaving it in gear and killing power to the engine to hopefully improve engine braking.
There's no need to do this, but it's also not going to hurt anything.
With the way these engines are setup you've already got no fuel going to the injectors if the throttle is at idle and the engine is turning faster than idle speed. The injection pump has a min/max governor built in and at min throttle (ie idle) it's going to completely shut off fuel injection when engine rpms are above the idle set point.
There's no loss of lubrication because you've still got full flow through the lift pump, transfer pump and injection assembly, just nothing getting injected. In fact you have *more* flow than at idle just do to higher rpm. (This is assuming you're shutting off fuel with the normal solenoid - if for some reason you added a fuel valve and shut that off yes you would cause problems.)
As long as the engine is still turning you'll still have full brakes and power steering. The only problem would come if you popped the clutch of stuck her in neutral for whatever reason, then you would lose it.
I am not sure if turning the engine off while still in gear is technically illegal - I know coasting in neutral is but not sure exactly what the letter of the law is. Probably is, but I doubt it'd ever really come up unless you got in a wreck somehow due to that.
Shutting off the engine with an automatic tranny would probably eventually cause the truck to hold back more, but only because the trans would probably blow up - the lube/pressure pump is crank driven, so killing the engine would starve the trans for lube oil. Bad idea.
So bottom line, I don't think it's as bad of an idea as some here, but it also wouldn't buy you anything. The only way to make it hold back better is an exhaust brake, which is an awesome addition, but quite pricy.....
To clarify, I'm assuming you have a manual trans and you're leaving it in gear and killing power to the engine to hopefully improve engine braking.
There's no need to do this, but it's also not going to hurt anything.
With the way these engines are setup you've already got no fuel going to the injectors if the throttle is at idle and the engine is turning faster than idle speed. The injection pump has a min/max governor built in and at min throttle (ie idle) it's going to completely shut off fuel injection when engine rpms are above the idle set point.
There's no loss of lubrication because you've still got full flow through the lift pump, transfer pump and injection assembly, just nothing getting injected. In fact you have *more* flow than at idle just do to higher rpm. (This is assuming you're shutting off fuel with the normal solenoid - if for some reason you added a fuel valve and shut that off yes you would cause problems.)
As long as the engine is still turning you'll still have full brakes and power steering. The only problem would come if you popped the clutch of stuck her in neutral for whatever reason, then you would lose it.
I am not sure if turning the engine off while still in gear is technically illegal - I know coasting in neutral is but not sure exactly what the letter of the law is. Probably is, but I doubt it'd ever really come up unless you got in a wreck somehow due to that.
Shutting off the engine with an automatic tranny would probably eventually cause the truck to hold back more, but only because the trans would probably blow up - the lube/pressure pump is crank driven, so killing the engine would starve the trans for lube oil. Bad idea.
So bottom line, I don't think it's as bad of an idea as some here, but it also wouldn't buy you anything. The only way to make it hold back better is an exhaust brake, which is an awesome addition, but quite pricy.....
79jasper
Chickenhawk
I think I know what you're talking about, with my 94 psd. It will get pretty quiet while coasting.
Then when you get back in it, you can feel it kick back to life. Almost like a split second push start.
firehawk
Full Access Member
Fuel injected cars will cut off fuel supply when the throttle is closed, but only above a certain rpm. Unless you can duplicate that, killing fuel is a bad idea.
swervyjoe
Full Access Member
OK, so I tried it on my way home today and couldn't feel a difference. This was on the flat ground in town, not coming off a mountain, but flipping the IP off, didn't feel any different than just letting off the go pedal
Sw1tchfoot
Full Access Member
Flipping a switch or holding a button down every hill is no benefit, it is an inconvenience. The amount of fuel injected into the engine while coasting at idle is so insignificant that such as idea is merely a safety hazzard.
