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Registered
Join Date: May 2002
Location: St Louis
Posts: 4,211
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DME CASIS question
I was just entertaining myself looking at Wilke's 84-88 DME schematic again.
It looks like the CASIS light drive comes off the injector driver (unknown custom part). The only input to the driver is a discrete from the micro controller, I assume being an injector on - off signal. So how does it work? Is the injector pulse width modulation synchronized with engine rpm? It seems like my light works as follows: Annoyingly low RPM part throttle it comes on. Wide open throttle some RPM it comes on. Take your foot off the gas in overrun it goes off. Does just the injector duty cycle have all this info in it? I'd ask this on diy-efi but it's been down for months. |
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10-07-2003, 02:12 PM
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Irrationally exuberant
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Here's another data point, maybe it's helpful:
The CASIS light also doubles as the Rev Limit light. Interestingly, even after you disable the CASIS light by disconnecting the black (?) wire on the back of the tach, the light will still come on when you hit the rev limit. I was looking at this circuit a while back. When I discovered it wasn't useful for my (evil) purposes I ceased my investigations. -Chris
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'80 911 Nogaro blue Phoenix! '07 BMW 328i 245K miles! http://members.rennlist.org/messinwith911s/ |
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10-07-2003, 03:11 PM
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Registered
Join Date: May 2003
Location: Manhattan Beach, CA
Posts: 2,350
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The light you mention is the up-shift indicator and comes "on"
when injection duty cycle reaches a preset value. This value is computed by the uP in the tach based on the DME output on pin 11. Have Fun Loren '88 3.2
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Have Fun Loren Systems Consulting Automotive Electronics '88 911 3.2 '04 GSXR1000 '01 Ducati 996 '03 BMW BCR - Gone |
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10-07-2003, 06:36 PM
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Back in the saddle again
Join Date: Oct 2001
Location: Central TX west of Houston
Posts: 56,185
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It seems to be dependent on more than just one thing because it does depend on throttle and rpms. Yes, if you are light in the throttle it will come on ridiculously early (for gov't emissions reasons, especially when it directly contradicts the minimum shift points in the owner's manual), if you are heavier on the throttle it will come on later, if you let off of the throttle it will go off (the computer shuts fuel off from the engine if the throttle is closed and you are over 1800 rpm), and it also comes on at redline.
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Steve '08 Boxster RS60 Spyder #0099/1960 - never named a car before, but this is Charlotte. '88 targa  SOLD 2004 - gone but not forgotten
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10-07-2003, 10:04 PM
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Registered
Join Date: May 2003
Location: Manhattan Beach, CA
Posts: 2,350
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All those things affect the injection duty cycle! Put a scope on pin 11
and see what happens for yourself. It's basically same as what you see on each injector w/o the inductive ringing. Have fun Loren '88 3.2
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Have Fun Loren Systems Consulting Automotive Electronics '88 911 3.2 '04 GSXR1000 '01 Ducati 996 '03 BMW BCR - Gone |
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10-07-2003, 11:16 PM
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The Blue Pheonix
