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0-Cylinder mode while coasting

TrueBlue
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TrueBlue Enthusiast

TrueBlue

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What exactly is happening when this mode activates? 

 

Is fuel cutoff, or is it something else?

davester Senior Enthusiast

davester

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Posted

what are you talking about?  dfm uses one of 17 cylinder patterns, from 1 to 8 cylinders being active.  They don't use a pattern wih zero cylinders enabled.

newdude Senior Enthusiast

newdude

Posted
Posted (edited)
8 hours ago, TrueBlue said:

What exactly is happening when this mode activates? 

 

Is fuel cutoff, or is it something else?

 

 

0 cylinder mode?  That would be deceleration fuel cutoff via the fuel system.

 

Any time an AFM/DFM engine enters DCFC, all cylinders go back to being active.  So the DFM solenoids close the oil flow to re-lock the lifter, and all 8 cylinders become mechanically active again.  Engine pumps on all 8 but they cut the fuel off.  So extended coasting (down a hill, long offramp, if you like to save brakes, etc.).  

 

DFM can skip fire on as little as one cylinder.  

 

Quote

 

The conditions listed below may be reasons for inhibiting deactivation:

 

  • Decel fuel cutoff is active

 

 

Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The ECM monitors the corresponding changes in throttle position, Mass Airflow (MAF), and Manifold Absolute Pressure (MAP). The ECM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to prevent damage to the catalytic converters.

 

Fuel Cutoff Mode

The ECM cuts OFF fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability:

 

  • The ignition is OFF. This prevents engine run-on.
  • The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.
  • The engine speed is too high, above red line.
  • The vehicle speed is too high, above rated tire speed.
  • During an extended, high speed, closed throttle coast down—This reduces emissions and increases engine braking.
  • During extended deceleration, in order to prevent damage to the catalytic converters

 

Here's a great detailed read from GM/Tula Technologies.  Tula is the one that actually created DFM, originally called Dynamic Skip Fire by Tula.  GM bought into Tula to get DFM into the updated Gen V engines.  @Grumpy Bear You'd probably love reading this if you haven't.  The list of side effects are rather interesting, and some of them came to fruition with AFM and now DFM (torque converter problems being one of them). 

 

Dynamic-Skip-Fire-New-Technologies-for-Innovative-Propulsion-Systems-Paper-Vienna-2018.pdf

Edited by newdude
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TrueBlue Enthusiast

TrueBlue

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Posted (edited)

Thanks for the info @newdude. Does this mean that it is not the typical DFM mode of collapsing lifters that is used to turn all eight cylinders off? Or does it mean that 0-cylinder mode, correctly labeled as Deceleration Mode, is simply DFM affecting all eight cylinders at the same time? Are all lifters collapsed in this mode?

 

edit: I read what you said more slowly. 

 

Any time an AFM/DFM engine enters DCFC, all cylinders go back to being active.  So the DFM solenoids close the oil flow to re-lock the lifter, and all 8 cylinders become mechanically active again.  Engine pumps on all 8 but they cut the fuel off. 

 

Closing the oil flow. This puts the lifters in non-DFM mode? Just as they would be if the engine is under load and pulling, but the cylinders do not fire because fuel is cut?

 

Edited by TrueBlue
newdude Senior Enthusiast

newdude

Posted
Posted
7 hours ago, TrueBlue said:

Thanks for the info @newdude. Does this mean that it is not the typical DFM mode of collapsing lifters that is used to turn all eight cylinders off? Or does it mean that 0-cylinder mode, correctly labeled as Deceleration Mode, is simply DFM affecting all eight cylinders at the same time? Are all lifters collapsed in this mode?

 

edit: I read what you said more slowly. 

 

Any time an AFM/DFM engine enters DCFC, all cylinders go back to being active.  So the DFM solenoids close the oil flow to re-lock the lifter, and all 8 cylinders become mechanically active again.  Engine pumps on all 8 but they cut the fuel off. 

 

Closing the oil flow. This puts the lifters in non-DFM mode? Just as they would be if the engine is under load and pulling, but the cylinders do not fire because fuel is cut?

 

 

 

In DCFC, all 8 cylinders are active.  The lifters are not collapsed allowing for deactivation.

 

In AFM/DFM lifters (same exact part), when oil pressure is applied to the internal locking pin, the lifter is allowed to collapse and perform cylinder deactivation.  When the solenoid closes, that oil pressure bleeds off quick and re-locks the pin, thus allowing the valves to be open and the cylinder is no longer deactivated.  

  • Thanks 1
TrueBlue Enthusiast

TrueBlue

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Thank you Sir. In my case I think this is a good thing. 

 

Do you happen to know whether or not DCFC is deactivated, along with DFM when in L9?

Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
12 hours ago, newdude said:

Here's a great detailed read from GM/Tula Technologies.  Tula is the one that actually created DFM, originally called Dynamic Skip Fire by Tula.  GM bought into Tula to get DFM into the updated Gen V engines.  @Grumpy Bear You'd probably love reading this if you haven't.  The list of side effects are rather interesting, and some of them came to fruition with AFM and now DFM (torque converter problems being one of them). 

 

Dynamic-Skip-Fire-New-Technologies-for-Innovative-Propulsion-Systems-Paper-Vienna-2018.pdf

Edited 11 hours ago by newdude

 

Serious complexity. Great read and thanks for the share @newdude

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