Does Coasting Reduce Piston Ring Contamination?

[JohnnyG]

Ignition still firing that mixture (oil) in the high vacuum - closed throttle scenario and there’s the potential for carbon…

With the throttle plate closed? Not likely. That oil ain't gonna ignite (if there is any).

 

[DGXR]

In a NA engine, pressure during the intake stroke is always less than ambient, though at full throttle it can approach ambient pressure.

Side note: LT6 is NA with "volumetric efficiency that exceeds 110%" -- the adaptive intake is a very slick design: LT6 Hemholtz intake

 

[PontiacHO]

We can have different opinions. One of the quickest way to determine if an engine is worn (rings, valve guides, and valve seals) is to downshift and coast-decelerate. What happens? Blue smoke. Yes, the oil burns.

 

[jtay2024]

We can have different opinions. One of the quickest way to determine if an engine is worn (rings, valve guides, and valve seals) is to downshift and coast-decelerate. What happens? Blue smoke. Yes, the oil burns.

Usually that's only when you re-apply the throttle and introduce fuel again to get it buring isn't it?

 

[MRC01]

Side note: LT6 is NA with "volumetric efficiency that exceeds 110%" -- the adaptive intake is a very slick design: LT6 Hemholtz intake

It's always been possible with valve timing, intake and exhaust geometry, to take advantage of the low and high pressure pulses and use that energy to boost intake efficiency. Porsche had varioram, Ford had IMRC, etc. Yet I never knew if any engine actually got intake efficiency above 100%. Interesting!

 

[Rmay635703]

A) If the engine is running, it's still burning fuel.
B) The vacuum increase is in the intake system, not the cylinders.

Where the drive side and coast side of ring and pinion gear wear can be observed, I don't know if the rings shift (up and down in their grooves) any between the two conditions.

A) is false, since the early 90’s many engines shut off the injectors when you are 1) in gear
2) and have your foot off the gas
3) are spinning over a certain RPM

I know for certain if I let off the gas in my cobalt XFE and RPMs are above 2000 per my gages MPGs go to 9999mpg trim is 0 and fuel use measures zero. Stays that way until about 1200rpm or if I hit the clutch or neutral.

What is unfortunate is that some motors don’t continue pulsing the spark to burn off VOC.

With the throttle plate closed? Not likely. That oil ain't gonna ignite (if there is any).

Some cars kill the ignition pulses, personally I prefer option 2 where the spark is really retarded but continues because any VOC and residuals can burn off.

 

[ARCOgraphite]

It's always been possible with valve timing, intake and exhaust geometry, to take advantage of the low and high pressure pulses and use that energy to boost intake efficiency. Porsche had varioram, Ford had IMRC, etc. Yet I never knew if any engine actually got intake efficiency above 100%. Interesting!

This is why with typical intake cam timing the valve is open well beyond bottom dead center - you have an inrush of a gas (air + fuel) that results in effective intake ram supercharging.

 

[another Todd]

A) If the engine is running, it's still burning fuel.
B) The vacuum increase is in the intake system, not the cylinders.

Where the drive side and coast side of ring and pinion gear wear can be observed, I don't know if the rings shift (up and down in their grooves) any between the two conditions.

In reference to B, the vacuum in the intake is caused by the pistons pulling the vacuum during the intake stroke with closed throttle plate (or partially closed). I would say the vacuum is equal or higher in the cylinder during the intake stroke than it is in the manifold due to intake valve obstruction (partial).

 

[nicholas]

A) If the engine is running, it's still burning fuel.
B) The vacuum increase is in the intake system, not the cylinders.

Where the drive side and coast side of ring and pinion gear wear can be observed, I don't know if the rings shift (up and down in their grooves) any between the two conditions.

Both of our vehicles shut off the injectors when coasting as speeds above 40kph
As seen on live obd2 data.

I'm sure I am not alone.

 

[SHOZ]

Both of our vehicles shut off the injectors when coasting as speeds above 40kph
As seen on live obd2 data.

I'm sure I am not alone.

It doesn't shut them completely off. Look at the your injector duty cycle when the CFSO is in play. Mine stays at 1 which is also the idle setting. It does shut off the O2s. On my Hyundais the long term doesn't zero out, short term does.

 

[nicholas]

It doesn't shut them completely off. Look at the your injector duty cycle when the CFSO is in play. Mine stays at 1 which is also the idle setting. It does shut off the O2s. On my Hyundais the long term doesn't zero out, short term does.

Both cars are at 0 until about 1300-1400 rpm then injector and short begin to move.

 

[SHOZ]

Both cars are at 0 until about 1300-1400 rpm then injector and short begin to move.

What's your commanded fuel lambda? 1.03 or so?

 

[oldhp]

When I had my Dodge 440 rebuilt the builder said after the first 100 miles to take the RPM's up to 3500 in second gear and quickly let off the gas pedal. "That will draw oil up past the rings to help clean and seal the cylinders." Didn't burn any oil past 800 miles.