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Old 08-15-2013, 03:46 PM   #4 (permalink)
t vago
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Originally Posted by Pawtuckett View Post
I'm not actually worried about it, just puzzled. I can't accurately calibrate my MPGuino because there is no set percentage that it is reporting over or under. I haven't changed the settings for a looooong while now, just to see how much the odometer & gas pump compared with the Guino. It's over AND under reported during said time, and I'm getting tired of feeling like I can't trust my instrumentation.
I hear ya there.

Hey, I just got a strange idea. The injector is fired by the PGM-FI by switching the ground on and off, right? So, the MPGuino sees a low-going voltage signal as the start of a fuel injector pulse. And, your kill switch removes power from the injector circuit, too, right? The MPGuino would see the same thing (a low-going voltage signal) when you actuate your kill switch, too. Basically, the MPGuino code you're using is interpreting that as a really long valid fuel injector pulse.

I have seen much the same problem with my re-written MPGuino code. When I first started testing the code, I'd get some really freaky large fuel consumption measurements, whenever my vehicle would enter EOC. Basically, I'd go from a tank average 23 MPG to around 1 MPG, all of a sudden. It was because the fuel injector measurement routines did not really do any sort of sanity checking.

I came up with two different rationality checks that are applied on each measured fuel injector pulse. Basically, if the measured pulse width is greater than what could be expected at some arbitrarily low engine speed (say, 400 RPM), then that pulse measurement is simply thrown out. Also, if the fuel injector pulse start is recorded, and a pulse end isn't received by about 0.5 seconds or so, then the pulse measurement itself is abandoned, and the code waits for the fuel injector signal to go high, then go low again. These two checks have eliminated the issue I've seen, and they may well eliminate your problem, too.

Originally Posted by Pawtuckett View Post
Is it even possible that tapping into the ECU for VSS and Injector pulse could give voltage readings that would be spiking erroneously upon activation of the kill switch? There may only be one way to know for sure, as you said.
No, I would not think this would cause your issue.
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