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Old 11-19-2012, 01:05 PM   #1
raymoon
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Revving Engine Pre-Engine Shutoff

I did a search and couldn't find a discussion on this topic.

Just thought of this after watching Casino Royale again. I'm talking about the scene when Bond pulls up for brunch in the DBS, parks, revs the engine and then shuts it off.

Anyways,

I've been doing some searches online and the most common answers were:

1. It's completely useless now. It was only used in engines with carbs to make it easier to start next time.

2. If you blip the throttle and turn the engine off with the engine revving, fuel will be cut off the moment ignition is off, clearing the cylinders of fuel and leaving it with fresh air (to prevent any type of...corrosion buildup?)

What's the word on this - and does ANYONE do it.
...just curious.
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Old 11-19-2012, 01:07 PM   #2
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Yes...ms43 and higher does this since there is no return fuel line from the fuel rail.

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Old 11-19-2012, 01:13 PM   #3
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Quote:
Originally Posted by flashtwosix View Post
Yes...ms43 and higher does this since there is no return fuel line from the fuel rail.
What's the line of thinking there? Not sure I follow.
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Old 11-19-2012, 01:14 PM   #4
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Old 11-19-2012, 01:15 PM   #5
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It's a movie.
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Old 11-19-2012, 01:17 PM   #6
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Originally Posted by Wh33lhop View Post
It's a movie.
You missed the point of this thread.


Either way...


Last edited by raymoon; 11-19-2012 at 01:23 PM.
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Old 11-19-2012, 01:33 PM   #7
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it MIGHT be helpful if you just want to move the car starting the engine cold then shutting it off immediately to prevent flooding (too much gas in the cylinders and on the spark plugs), which can cause hard starting.
on a rotary engine its suggested revving the engine then shut it off if the engine is cold (rotary engines are much easier to flood).
if the engine is warm, dont worry about it.
as for the movie, its just for show.
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Last edited by jasonbimmer; 11-19-2012 at 01:35 PM.
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Old 11-19-2012, 01:38 PM   #8
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What's the line of thinking there? Not sure I follow.
Agreed, please elaborate flashtwosix.

And yes obviously the movie was for show. It's just what made me think about the concept. Just trying to see IF there is anything actually beneficial about doing it.

Last edited by raymoon; 11-19-2012 at 01:45 PM.
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Old 11-19-2012, 01:41 PM   #9
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Yea. I had a buddy once that would always rev his prelude to let you that he'd arrived. The point is to try to get others to think you are cool.
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Old 11-19-2012, 02:12 PM   #10
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When I get home let me pull up the ms43 literature for the official explanation

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Old 11-19-2012, 02:42 PM   #11
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I would imagine shutting off the engine while at idle is the same as shutting it off at a higher RPM--except with more fuel. Don't see any point to it whatsoever.

I think what flash is saying is that modern bmws and other modern cars as well continue to fire one or two of the cylinders after shutdown to burn off any fuel and smooth out engine shutdown (more refined)
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Old 11-19-2012, 02:42 PM   #12
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Since the fuel Injection for a cylinder happens during the down stroke of the piston and the ignition happens at close to the top of the next stroke, fuel is injected and compressed in the cylinder.
If you turn the key off after the fuel injection and the spark plug doesn't fire you would have unburned fuel left in the cylinder.

BMW made a change with the MS43 ECU to continue the ignition for two more cylinders after the key is turned off.

Page 16 - http://www.bmwmotorsports.org/BMW_docs/m54x5.pdf

MS 43 NEW FUNCTIONS
EMISSION OPTIMIZED - IGNITION KEY OFF

"Emission Optimized Ignition Key Off" is a programmed feature of the MS 43 control module.
After the ECM detects KL 15 being switched OFF, the ignition stays active for two more
individual coil firings. This means that just two cylinders are fired - not two revolutions.
This feature allows residual fuel injected into the cylinders, as the ignition key is switched
off, to be burned as the engine runs down.
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Old 11-19-2012, 02:48 PM   #13
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My buddy in high school used to do it in a POS Mitsubishi Galant from the 70s, swore it gave the battery just enough more juice on the next startup. I personally didn't buy it, given how few extra turns the alternator actually got.
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Old 11-19-2012, 02:55 PM   #14
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Originally Posted by cvx5832 View Post
My buddy in high school used to do it in a POS Mitsubishi Galant from the 70s, swore it gave the battery just enough more juice on the next startup. I personally didn't buy it, given how few extra turns the alternator actually got.
You're correct. That's retarded.
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Old 11-19-2012, 02:59 PM   #15
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Because Bond, James Bond. Also, maybe because it wasn't his car and he wasn't used to driving it!
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Old 11-19-2012, 03:25 PM   #16
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Quote:
Originally Posted by shanneba View Post
Since the fuel Injection for a cylinder happens during the down stroke of the piston and the ignition happens at close to the top of the next stroke, fuel is injected and compressed in the cylinder.
If you turn the key off after the fuel injection and the spark plug doesn't fire you would have unburned fuel left in the cylinder.

BMW made a change with the MS43 ECU to continue the ignition for two more cylinders after the key is turned off.

Page 16 - http://www.bmwmotorsports.org/BMW_docs/m54x5.pdf

MS 43 NEW FUNCTIONS
EMISSION OPTIMIZED - IGNITION KEY OFF

"Emission Optimized Ignition Key Off" is a programmed feature of the MS 43 control module.
After the ECM detects KL 15 being switched OFF, the ignition stays active for two more
individual coil firings. This means that just two cylinders are fired - not two revolutions.
This feature allows residual fuel injected into the cylinders, as the ignition key is switched
off, to be burned as the engine runs down.
This seems to answer it. With our cars its absolutely useless because of the additional firing of 2 cylinders. Ohh.. BMW engineering.
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Old 11-19-2012, 03:28 PM   #17
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It was even bad back then. Unburned fuel sitting on top of the cylinder could leak past the rings into the oil and get into your crankcase which is not a good thing at all.

Nowadays I guess it doesn't matter.

Last edited by 330iPilot; 11-19-2012 at 03:29 PM.
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Old 11-19-2012, 03:37 PM   #18
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This seems to answer it. With our cars its absolutely useless because of the additional firing of 2 cylinders. Ohh.. BMW engineering.
useless for any electronically fuel injected car. (which is pretty much all cars)
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Old 11-19-2012, 03:42 PM   #19
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The reason is to clear fuel from the cylinders. It has the added benefit of making intimidating engine noises to scare potential competitors (either at the valet or the race track). Needless on cars with EFI since at most you'll have one combustion cycle worth of fuel in the cylinder which will evaporate within seconds in a still hot engine.

Quote:
Originally Posted by flashtwosix View Post
Yes...ms43 and higher does this since there is no return fuel line from the fuel rail.

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No, and it has nothing to do with no return line from the fuel rail. Shanneba gave a good explanation, and the key words to acknowledge are emission optimized. Letting gasoline evaporate is wasteful and is not good for the environment.
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Old 11-19-2012, 03:47 PM   #20
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Quote:
Originally Posted by E46Mango View Post
useless for any electronically fuel injected car. (which is pretty much all cars)
.. but not including the Aston Martin DB5. Don't know if it had an electric fuel pump. If it was mechanical, it would have continued to pull gas into the cylinders after the sparks were shut off.
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