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Old 06-17-2013, 05:24 PM   #5 (permalink)
t vago
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Originally Posted by NachtRitter View Post
Interesting! Thanks for the explanation.

Sounds like you'll be taking a reading off the manifold pressure (along with the injector pulse) so you can emulate the ECM?

Any particular reason you didn't go with an OBDII approach (OBDuino, Scangauge, etc)?
I currently use an Ultragauge in the Karen-mobile, and a ScanGauge II in the Fiat Dakota.

Not sure about the OBDuino or the Scanguage, but I know for a fact that the UltraGauge cannot accurately show the effect of the ecomods I have done to the engine of the Karen-mobile. For instance, this post about initial EGR sensor modification results showed a real-world fill-up FE figure of 25.8 MPG. However, the Ultragauge only recorded a per-tank average of 23.9 MPG. This, after I had previously calibrated the Ultragauge to get its average FE reading to within 0.2 MPG of the calculated fill-up FE figure. It's very likely that it has something to do with the way that the Ultragauge estimates fuel consumption. If I am lowering intake manifold via increasing EGR opening, then the MAP sensor reading will reflect that, and the Ultragauge is likely showing that as a artificially lower fuel economy figure.

The Scangauge is likely going to use some version of MAF to estimate fuel consumption. The OBDuino get_icons function actually does do this -> "formula: (3600 * MAF) / (14.7 * 730 * VSS)".

The only way to really get around that, IMO, is to directly measure fuel consumption. The MPGuino is still going to provide an estimate, but it should be very accurate, compared to the estimation formulas used in OBDII instrumentation. I got a couple of MAP sensors laying about, so I can get both ambient and intake manifold pressures with little effort. The JellyBeanDriver version of the MPGuino has hardware provisions for collecting 2 different analog signals, and it should be a relatively simple matter to code in a simple square root function.
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