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Last edited by FR Wilk; 04-11-2007 at 05:48 AM..
Old 11-21-2003, 01:40 PM
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That would be twice per cycle.
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Old 11-21-2003, 04:08 PM
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Hello FR,

To a simple layman like myself, such a firing scheme seems a bit wasteful. Why don't they fire one at a time at the precise moment they are needed?

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DL
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Old 11-21-2003, 05:56 PM
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Back in the early 70's when I went through the VW/Porsche fuel injection school I was told that the injectors can open and close only so fast or stay open just so long. Bosch determined that they could fire on top of the closed valve then again as the valve opens for the intake stroke. Twice per cycle.

This is in contrast to the CIS used on the early 924's where the injection was a contant spray with out regard to engine cycles.

The split wire loom to the DME does tend to throw one off.

I've often wondered if two injectors per intake could be used. Would give a broader range of fuel flow.
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
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Old 11-21-2003, 06:19 PM
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Re: All 4 injectors fire at once

Quote:
Originally posted by FR Wilk
Some confusing emails lately. 944s do not bank fire. All 4 injectors fire at one time.
Actually this is bank firing, but you only have one bank and one injector driver. Many pre 1995 EFI systems worked this way.

Most current EFI systems use sequential firing, with a driver for each injector. But don't worry, they didn't do this for performance reasons. With individual drivers the computer has total control over each injector. When the OBD II system senses a misfire that exceeds the threshold limit it can turn fuel off to that individual cylinder and prevent sending that un-burnt fuel to the cat. After a predetermined time it may refire the injector and monitor it again.

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Old 11-21-2003, 09:15 PM
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