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Old 06-06-2007, 04:02 PM   #11
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bbgobie -

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Originally Posted by bbgobie View Post
I thought I read somewhere here that if the car is in gear but your coasting that because the tranny is connected its actually turning over the engine so no fuel is required. It didnt make sense to me as I've always been of the train of thought the faster your engine is reving the more fuel is required to keep it turned over even if you are coasting.

I may have misread or misunderstood. Either way, as long as the scangauge is accurate about fuel consumed I can figure out what works best for my car.
Some ECU/PCMs say "Driver is in gear but foot off pedal (coasting), I will turn off injectors". Other ECU/PCMs say "Drive is in gear but foot off pedal, I will reduce fuel injection to a minimum". My Saturn does the latter.

Here is what I have noticed. When my Saturn coasts in gear with a minimum amount of fuel injected, it loses speed (duh). However, if I cut the ignition with the car in gear and coasting, it slows down faster.

I have seen in at least one instance with a diesel, that the instant MPG goes to 9999 when I coast in gear. 9999 is the equivalent of infinity for the ScanGauge, since 0 fuel injection is a divide by zero condition. This tells me that the diesel is practicing fuel cutoff.

Soooooooooo, not all drivetrains are the same. The following is specific for Saturns. I got this from :

Engine Temps - Coasting To a Stop
http://www.gassavers.org/showpost.ph...8&postcount=23

-----------------------------------------------------------

Negative Fuel Trim...Constant
http://www.saturnfans.com/forums/showthread.php?t=89959
Quote:

Bigdaddy94sc2 says :
For STFT to drop when slowing down is normal, due to decell fuel cutoff. 25% is the max it can go to, then it goes into decel fuel cutoff when it sees brakes applied, speed decreasing, and no ABS activation. It doesnt totally cut fuel, but darn close.
Other drivetrains are much better at this and can be very thrifty about cutting fuel when the right combination of driving events appear to the ECU/PCM, i.e. a certain combination of "0 throttle + in gear + brakes applied".


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Old 06-06-2007, 07:43 PM   #12
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Why don't all car makers go with the foot off gas, in gear, lets shut off fuel scenario? Seems like it has the same effect of shutting off the engine until you reach an rpm at which it won't turn over the engine and you have to start re-injecting fuel to turnover.

Quote:
Originally Posted by cfg83 View Post
bbgobie -



Some ECU/PCMs say "Driver is in gear but foot off pedal (coasting), I will turn off injectors". Other ECU/PCMs say "Drive is in gear but foot off pedal, I will reduce fuel injection to a minimum". My Saturn does the latter.

Here is what I have noticed. When my Saturn coasts in gear with a minimum amount of fuel injected, it loses speed (duh). However, if I cut the ignition with the car in gear and coasting, it slows down faster.

I have seen in at least one instance with a diesel, that the instant MPG goes to 9999 when I coast in gear. 9999 is the equivalent of infinity for the ScanGauge, since 0 fuel injection is a divide by zero condition. This tells me that the diesel is practicing fuel cutoff.

Soooooooooo, not all drivetrains are the same. The following is specific for Saturns. I got this from :

Engine Temps - Coasting To a Stop
http://www.gassavers.org/showpost.ph...8&postcount=23

-----------------------------------------------------------

Negative Fuel Trim...Constant
http://www.saturnfans.com/forums/showthread.php?t=89959


Other drivetrains are much better at this and can be very thrifty about cutting fuel when the right combination of driving events appear to the ECU/PCM, i.e. a certain combination of "0 throttle + in gear + brakes applied".


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