map reversing

Developer topics relating to software that provides a tuning UI to alter ECU code and data

Moderator: Freon

Postby Freon » Sat Dec 01, 2007 4:22 pm

Jon, I used the equation he posted. I'm purposely generalizing.

Opening a real definition from a Denso SH-2 ROM, the decimal actually starts out at 0 and adds fuel from there. A value of 0 is no fuel enrichment (1.0 lambda, closed loop, or equivalent 14.7). A value of 128 (0x80) would be 7.35:1 equivalent, and 255 (0xFF) would be down near 5:1. It does seem like a waste of precision because you'll probably never use a value over 50 (about 10.0:1). Yes, the divide instruction explanation makes sense. Note, the SH-2 CPU still uses this storage even though the execution speed and division issues do not matter due to its instruction set. Carry over perhaps.

What's wrong with allowing to -20 BTDC timing? I don't see the problem with that. Given sufficient load, compression ratio, it could be necessary. Ignition timing is about controlling peak cylinder pressure which is almost universally going to target around 15-16 ATDC. It could be that your combustion could take less than 15-16 degrees of crank rotation. There is nothing special about TDC as far as triggering the start of combustion. Nothing special happens at that point, and it is not a limit.
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Postby letsteyr » Wed Dec 05, 2007 9:48 pm

I got a new question: if i want to extend a map (more axis values), is it possible to do it easyly on 32bit ecu? I suppose I've to find a blank space, to cut and paste my map to this space then to change the adressing in the begining of the file (where all maps are defined). Is there anything else to do cause i suppose the ecu has to go to these defs first to be able to locate the map?
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Postby letsteyr » Tue Dec 11, 2007 2:19 am

no idea?
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Postby Freon » Tue Dec 11, 2007 8:38 pm

What you're getting at is possible.

You can stretch the map out as it stands in the editor. The Subaru SH-2 ECUs use a very precise linear or bilinear sample technique when retrieving data.
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Postby letsteyr » Wed Dec 12, 2007 9:26 am

cool. I won't try it now but i'll do one day. Thanks
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