gas cut off?

[flair1111]

ive been reading lately that if you have overdrive locked out that if you have a hard deceleration, that the engine in our KJs will cut off the gas feed to the engine.

If this is the correct understanding, then what constitutes a "hard deceleration"?

Im hoping that this might act like the Volkswagen Jettas and some of their other cars...or so ive read....in that when you take your foot off the gas, the engine is cut off from a gas feed until the gas pedal is applied again. from my understanding, this applies at almost all speeds in the VW models that do this... so...just when exactly does this occur in our KJs? is it over a certain speed, or at a certain G force that is recognized?

a thank ya.

 

[Dave]

ive been reading lately that if you have overdrive locked out that if you have a hard deceleration, that the engine in our KJs will cut off the gas feed to the engine.

If this is the correct understanding, then what constitutes a "hard deceleration"?

Im hoping that this might act like the Volkswagen Jettas and some of their other cars...or so ive read....in that when you take your foot off the gas, the engine is cut off from a gas feed until the gas pedal is applied again. from my understanding, this applies at almost all speeds in the VW models that do this... so...just when exactly does this occur in our KJs? is it over a certain speed, or at a certain G force that is recognized?

a thank ya.

Correct. It is called DFCO......(Deceleration Fuel Cut Off) and my scangague confirms it. I have noticed it either in D or O/D going down mountains so mine seems to do it a few seconds after I let off the gas on a long downhill run. I am not positive but it seems like the computer senses the decelleration and cuts off fuel.........but I then pay for it on the uphill climb.

Dave

 

[tjkj2002]

It will happen in any gear in the KJ and at any speed.It is not listed the exact requirements on how/when it happens in the KJ but it does happen.It mainly has to do with the TPS location,engine RPM,and a few other things but the brake pedal has little to due with the inacting of it.Long,steep desents whne your foot is off the gas/brake it will cut fuel to try and maintain current speed and/or lower it.Basically the same concept as the deisels Jake Brake system.

 

[flair1111]

It will happen in any gear in the KJ and at any speed.It is not listed the exact requirements on how/when it happens in the KJ but it does happen.It mainly has to do with the TPS location,engine RPM,and a few other things but the brake pedal has little to due with the inacting of it.Long,steep desents whne your foot is off the gas/brake it will cut fuel to try and maintain current speed and/or lower it.Basically the same concept as the deisels Jake Brake system.

ok that is very helpful. so in essence when this happens, it keeps the engine running on just compression alone? I realize you said ...

"It is not listed the exact requirements on how/when it happens in the KJ but it does happen"...


i wonder if there is some way to find out the exact time it does happen, and then at what speed the regular idle (with gas) picks up again when you get close to stopping, and or, getting below a certain speed.


i needs to get me an EVIC for sure, but still.

 

[tjkj2002]

ok that is very helpful. so in essence when this happens, it keeps the engine running on just compression alone? I realize you said ...

"It is not listed the exact requirements on how/when it happens in the KJ but it does happen"...


i wonder if there is some way to find out the exact time it does happen, and then at what speed the regular idle (with gas) picks up again when you get close to stopping, and or, getting below a certain speed.


i needs to get me an EVIC for sure, but still.

Very easy to do............

Get in the KJ,lockout OD(just makes it easier to do) and run up to 75mph and let off the gas,do not touch the brake,and as soon as you start to feel/hear the engine pull you down(with a aftermarket muffler it will start to cackle) that is when it is cutting off fuel,then as soon as you get back on the gas you will feel a slight lag then your accelerating again,then let off and you will feel/hear it again.It makes it easier to feel/hear when going down hill as it has a unique sound and feel,just remember do nkt use the brakes.If you had a EVIC and it was displaying instant MPG's you would see it max the scale out at like 99.9mpg's.

 

[Dave]

i needs to get me an EVIC for sure, but still.

My EVIC only reads average mpg and not instantaneous mpg. (I am guessing all are the same). If you are going down hill and in DFCO, the only way to get the EVIC to read at that instantaneous moment in time is to push the reset button and it will then read 999mpg......until you get to the bottom of the mountain and hit the gas. Then it will go back to averaging the mpg. I have done this.

Just get a scangague. You can plug it in any vehicle made after 1996 and OBD11 compliant. You just plug it in the OBD11 port. It has many more settings than the EVIC. It will read instantaneous and average mpg as well as a bunch of other things.

Dave

 

[flair1111]

Very easy to do............

Get in the KJ,lockout OD(just makes it easier to do) and run up to 75mph and let off the gas,do not touch the brake,and as soon as you start to feel/hear the engine pull you down(with a aftermarket muffler it will start to cackle) that is when it is cutting off fuel,then as soon as you get back on the gas you will feel a slight lag then your accelerating again,then let off and you will feel/hear it again.It makes it easier to feel/hear when going down hill as it has a unique sound and feel,just remember do nkt use the brakes.If you had a EVIC and it was displaying instant MPG's you would see it max the scale out at like 99.9mpg's.

i dont have an after market muffler, but i will try this anyway and see if i can hear/feel the difference like you say.

come to think of it i think i have felt/heard this before, especially the delay when hitting the gas again. interesting......