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Old 04-09-2012, 03:56 AM   #4 (permalink)
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Probably not, but it won't change that often I would think.

Inj Pulse Width is the variable I'd be reading, and at 10.4kbps it should be OK to query the parameter once every 100ms or 200ms. For the 100ms (or 200ms) between reads, I'd assume it was identical.

This is what happens with the OBDuino *anyway* using the MAF sensor - with an assumed stoich, so I fail to see it being any less accurate. It should be more since I would be monitoring the pulse width of the injectors and won't care if it's rich, lean or at stoich..

I think the conclusion is - for the most accuracy you need two flow meters - fuel supply and return, and that gives you true flow of fuel.
I won't have that, so the next best are:
- MAF - somehow convert V to Gm/s and use OBDuino and assume Stoich, calibrate it to the tank so that variations in Lean / Rich are part of the calibration..
- Monitor speed & Inj Pulse Width, calibrate that so that the inj open /close times worked into it's calibration just as per OBDuino.
- Low level, monitor injectors for open close, and speed low level, and calibrate that for the error margin it also has worked into it.

No matter which monitoring method, there'll always be calibration to try and adjust it to suit.

MAF doesn't know about lean / rich so assumes stoich (and I have to find a way to convert from V to gm/sec - sounds difficult).
Inj Pulse Width - there's a delay added which is the time spent asking for the data, it ignores the open /close times, but that falls into the calibration just as the MAF version of OBDUino would.
Low level - this doesn't consider inj open / close times, and so is fudged to suit using calibration.

Of those 3, I think Inj Pulse Width is more accurate compared to MAF as the engine wouldn't always run at stoich. I'm just concerned I haven't thought of something.. (why would OBDuino not use Inj Pulse Width?)

The difficulty for 'en masse' usage might just be knowing the size of the injectors..?
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