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Old 08-27-2010, 08:17 PM   #12 (permalink)
cfg83
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1999 Saturn SW2 - '99 Saturn SW2 Wagon
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some_other_dave -

Quote:
Originally Posted by some_other_dave View Post
As to why your car drops out of DFCO after a while, there are almost always RPM limits for DFCO. After all, if they left the injectors off all the way down to 0 RPM, you'd have to use the key to start again and that wouldn't be so great.

It is also possible that Ford engineers decided that running in DFCO for more than X amount of time ran some risk they didn't want to run. I'm not sure what sort of risk that could be, though. You should still be pulling a vacuum so the brakes should keep working; with no fuel and no spark you shouldn't be putting a thermal load on the engine (just compression heating which isn't nearly as much as combustion heating); the field coil on the alternator should still be energized so the charging system should still be charging... No, no idea why they'd do that.

-soD
My car usually exits DFCO around 2500 RPM in 3rd or 4th gear. I wish it was around 1000 RPM, but maybe that's too close for comfort because idle RPM is about 850.

If the Ford has unheated oxygen sensors, then a long period of time would cool off the sensor and it wouldn't read correctly. A cold oxygen sensor would encourage the ECU/PCM to switch from closed-loop to open-loop mode, which is not good for MPG.

CarloSW2
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Last edited by cfg83; 08-27-2010 at 08:58 PM..
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