exactly 100kpa... wtf? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 01-03-2009, 08:43 AM   #1
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Default exactly 100kpa... wtf?

Pretty sure I've seen something about this before, but for the life of me I can't remember where, or if there was a fix...



Anyone remember seeing something like this?

Doesn't seem to affect driving weirdly

(currently running a test version of code for PID Idle control, but it did it on the latest release version too HR_11c1)

Cheers
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Old 01-03-2009, 09:49 AM   #2
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I'm not familar with reading those graphs. But are you saying you are always reading 100kpa. If so, you vacume line to the ms is off. It happened 2 days ago to me.
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Old 01-03-2009, 10:01 AM   #3
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Nononono. This is happening to him in decel- see how the throttle is closed, RPM is decreasing, and MAP is 12 kPa on either side of the event?

The problem is your kpafactor4250.inc file. I'll bet if you open up the version that's in \Program Files\MegaSquirt\MegaTune2.25\mtCfg\ you'll find that the first three rows are all "100T" and the smallest valid entry is "12T". So when a value of 10 or 11 is reported, MegaTune is considering it an error condition and defaulting to 100 instead.

Check inside the \src\ directory in the HR distribution folder. In it, you should find an updated version of the kpafactor4250.inc file which has the correct values. Copy that file into \Program Files\MegaSquirt\MegaTune2.25\mtCfg\ and the problem will go away.


I think I understand why this happens, too. I D/L'ed the datasheet for the MPX4250, and it claims that the lowest value the sensor is guaranteed to reliably report is 20 kPa, so the MS developers must have thought they were leaving enough headroom by scaling it all the way down to 12. But analog devices being what they are, the thing does occasionally emit a voltage which gets encoded as ADC001 or ADC002 by the processor, and in the original file, those values are assumed to be an error condition. They're not. So the new file allows for these ultra-low values to be interpreted properly.
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Old 01-03-2009, 04:15 PM   #4
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joe, as usual you come up trumps! many thanks I'll get that sorted!
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