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2007 Infiniti M35x (awd), 3.5L VQ series, automatic
My car has an OEM iFCD bar graph and tank average MPG. Over the past 2 years I've been able to use the iFCD with great success. During that time the car's calculated ave mpg and my spreadsheet have been within 2% of each other at every fill up. This is not bad considering I use various gas stations and pumps.

I got a SGII last week and hooked it up immediately. I set the engine specs and tank size. I then noticed that the SG iFCD # was much higher than the OEM #. Specifically it's 20-25% higher, which I feel is a big discrepancy.

Couple days in and some hunting around here I went to compare the speedo on the car/SG/GPS. I changed all the units to metric since many say the SG is more accurate that way. Between 60-80kph the max delta is only 0.2-0.3km. I don't feel that this is too great considering the various updating times that the SG and GPS display at. I was able to find several 10-30 sec sample periods, but in metro DC it's tough to find a flat empty piece of road to test these values for extended periods (1-2min) of time. My next step may be a second GPS.

I've read that people have bumped the engine displacement value to compensate for FE differences from manual calculations. But to me that seems like quite a big adjustment to account for a 25% deviation.

I just completed my first fill up and reset the fill up controls on the SG. I guess we'll see how this tank plays out. Any thoughts?

Before you go to that trouble compare the distance readings of your odometer (or GPS) to what the ScanGauge reports. The offset for distance and speed are exactly the same so you should use distance instead -- it is much easier to calibrate. The longer the distances you compare, the more precise you can get the offset, too.

Before you go to that trouble compare the distance readings of your odometer (or GPS) to what the ScanGauge reports. The offset for distance and speed are exactly the same so you should use distance instead -- it is much easier to calibrate. The longer the distances you compare, the more precise you can get the offset, too.

Sean, I found that on my Accord the speedometer reads about 3% over but the odometer reads around +0.5%. Not sure why that is, but it was confirmed with my GPS. I do agree with using the distance instead of speed.

ETA: Just thought of this, the previous owner replaced the instrument cluster so that may have something to do with it.

Thanks. I'll check that in a week when I fill up again.

Right-o -- I've calibrated the SG to GPS in the Elantra because the odometer is off a bit.

Might want to check the fuel cutoff value to see if the default 24 makes sense for your car.

Before you go to that trouble compare the distance readings of your odometer (or GPS) to what the ScanGauge reports. The offset for distance and speed are exactly the same so you should use distance instead -- it is much easier to calibrate. The longer the distances you compare, the more precise you can get the offset, too.
Just filled up again this morning and tried to make corrections. Let me know if I got this correct.

SG read 322 tank miles. Car read 329.5mi [1-(322/329.5)]x100 = 2.276%

From the manual:
MORE>SETUP>SPEED
"Both speed and distance can be adjusted to compensate for changes in tire size, gears, tire wear, etc."

First, when I'm at this screen the number in the top row doesn't have the percent sign like the manual shows, but that probably doesn't mean anything. Also I don't have a DISTANCE screen so I assume changing this one percentage, even though listed under SPEED, also affects distance. I raised the value to 2. Maybe I should round the above math up to 3 but we'll see how it goes for now.

Secondly, at the FILLUP screen the SG displayed 12.x gallons used and I pumped 17.5gal. I bumped this value up to the correct amount which displayed a 35.6% delta. Seems really high to me.

There is nothing I've read to say I should only be adjusting one parameter at a time, but maybe that is best practice. Ooops



Might want to check the fuel cutoff value to see if the default 24 makes sense for your car.
I've read the manual on this too and need help making sense of it.
TPS is one of the gauges I typically run. Idle is at 1.

When I'm coasting at low speeds the ifcd reads 60-110mpg (numbers before adjustments above)and TPS is 1. High speed coasting or steep downhills invokes the 9999mpg and sometimes the TPS is at 1 and sometimes it goes to 0.

From the manual:
"The setting is not critical, but is best if about 4 above the no-throttle TPS valus."

If my car idles at 1 TPS when warm do I adjust the default value of 24 down to 1+4=5?

Is making this cutoff change going to affect my fillup adjustment noted above? I figure I'm probably going to need to scale that back again.

You are correct that the single correction factor affects distance and speed at the same time. 2% is a good start and probably will match pretty well.

Your fuel offset is pretty major -- was the fillup reset sometime during your tank or did you add the ScanGauge after running the tank down about 4g from full?

You don't have to adjust one parameter at a time.

I can't help with the cutoff setting as my Elantra doesn't have that feature and the Insight has the older ScanGauge I which has no cutoff setting in it.

I'm sure the SG was not adjusted since my last fillup and it has been plugged in the whole time.

This was my 2nd fill. The manual suggests only resetting the fillup at the 1st fill and then adjusting the fuel offset at the 2nd fill. I've done exactly that.

I guess it'll be another couple weeks to find out. Hopefully someone can chime in with knowledge of the fuel cut function in the mean time.

Do you trigger the indication (9999) of fuel cut on the ScanGauge often? If it is too aggressively set and reporting fuel cut when your engine isn't actually in that state it could account for the large discrepancy in consumption rates.

Hi BME:

While the 2% speed/distance offset does not seem out of the ordinary, the 35% FE/Fuel consumed offset does seem larger than expected. Are you positive the displacement value is set to 3.5L to match your vehicle? If so, leave the fuel fill offsets as they stand. Never take the SG out of your Infiniti and install it in anything else or the cumulative fuel consumption, fuel economy and distance, values will not be worth anything.

All said, if a 35% gallons consumed correction matches the car, your done and you go with it.

Good Luck

Wayne

Update from my 5/30/10 fill up:
The delta between my adjusted speed/distance value of 2% and actual readings is still 0.70% low. I may let it play out a few more fill-ups before adding it to the 2.276% I noted on 5/20 and entering 3% into the SG.

At fill up I readjusted the fuel consumed offset down a few clicks to about 33.5%. Still high, but seems to be working at that level.

The SG tank FE matched the OEM gauge and was only slightly off the hand calculated value. Good news.

I am triggering the 9999 indication far less than before.

I'm confident I've got the engine displacement set correctly. I even went as far as checking the exact displacement to make sure Infiniti wasn't claiming 3.5l and it actually being 3401cc or 3599cc. IIRC it's 3495cc.

I'm wondering if the AWD is such a drag that it is sucking up a significant amount of FE, beyond what the engine computer thinks.