Volumetric Efficiency %

[Tommyjarvis2756]

After doing some research (and logging some settings), You guys have 1 VE% setting that would be the default if left blank, or that can be set manually. Default I believe is what, 85%. Without any calibration, adjusting this setting lower registers higher MPG readings across the board in the realtime mpg.

Any calculation of engine VE% I"ve found is referring to the VE @ the redline rpm's. In this case, my 1998 Camry LE 2.2l supposedly is 80% at that point. Would it be beneficial to find the VE% value for my average RPM's, input that value instead, and THEN start doing the fillup calibration adjustment?

[Tommyjarvis2756]

I should mention that these vehicles evidently DON'T have a MAF sensor, nor does the Lamda readings register which would make the MPG readings more accurate. I saw at the bottom of this post where someone made a script, but using VE 100%

[Weston@PPE]

DashCommand defaults to 75%, but it uses this same value across the entire RPM range. VE is used to calculate MAF, from MAP, IAT, VE, and the engine displacement. So yes, setting this lower would result in a higher MPG reading for vehicles that don't support SAE.MAF. If your car supports the SAE.MAF PID, we don't use the VE Vehicle Setting.

I assume you also calculate MPG by hand at the pump? If you are, I wouldn't start tinkering with settings like this unless the average MPG in DashCommand is just plain wrong. If DashCommand is within ~10% of your actual MPG there isn't a really a reason to change it.

[Tommyjarvis2756]

Awesome! That's basically what I ended up doing, by just starting from scratch (erase data, re-enter a new default VE). 70% seems to be just absolutely spot on, So a few more trips back and forth to work repeating the process should give me a good confirmation. Thanks once again!

Tom

[Xtropy]

Just curious here...

My Mazda 3 has a 2.0L (122 ci), that makes 148 ft-lbs @ 4100 RPM

Using the formula provided I get:

(9411 * (148 * 4100 / 5252) * 0.45) / (122 * 4100)

Which comes out to 0.98 = 98% efficiency.

So without adding anything into the Volumetric Efficiency % settings, DashCommand will use 98% or 75%? If I manually enter a number into the VL%, will this override the automatic settings or does it make no difference since my car supports the SAE.MAF PID?

I am finding that DashCommand is drastically overestimating my fuel economy and trying to find out how to get this more accurate. I get told that I will get about 900KM/per tank of gas and 5.6L/100KM yet after 2 months of manually logging my fuel economy numbers at each fill up, I have never gotten below 6.5L/100KM and average around 7.4L/100KM and 700KM/tank.

I don't want to track the entire fuel tank using the Fuel tab as I don't use DashCommand 100% of the time and hoping playing around with the VL% numbers would help get more accurate fuel consumption data.

Thoughts/comments? Thanks...

[Weston@PPE]

If you don't change any settings in DashCommand, it would default to 0.75 (75%). DashCommand itself doesn't even try to calculate VE, it just uses 0.75 no questions asked.

That formula gives your peak VE, but the engine is usually running lower than its peak VE, so it might not be the ideal VE to enter if you're looking for accurate fuel economy numbers. Also if your car has SAE.MAF, DashCommand won't use VE either way.

Have you ever used the fillup screen? If you've used it without monitoring the whole tank, it would have skewed your fuel economy numbers. If you're looking to calibrate it a little more without doing a full fillup procedure, you could reset your fuel economy data and then do a few short fillups. So reset, top off your tank, and then monitor all your driving for 2 days or so -- and fillup again. Then use the fillup screen to correct the amount of fuel you used. You could do this 2 or 3 times and it would probably get a lot more accurate. You don't need to continue doing fillups in DashCommand, once it gets where you want it you could just drive it and not worry about monitoring everywhere you go.

[Xtropy]

If you don't change any settings in DashCommand, it would default to 0.75 (75%). DashCommand itself doesn't even try to calculate VE, it just uses 0.75 no questions asked.

That formula gives your peak VE, but the engine is usually running lower than its peak VE, so it might not be the ideal VE to enter if you're looking for accurate fuel economy numbers. Also if your car has SAE.MAF, DashCommand won't use VE either way.

Have you ever used the fillup screen? If you've used it without monitoring the whole tank, it would have skewed your fuel economy numbers. If you're looking to calibrate it a little more without doing a full fillup procedure, you could reset your fuel economy data and then do a few short fillups. So reset, top off your tank, and then monitor all your driving for 2 days or so -- and fillup again. Then use the fillup screen to correct the amount of fuel you used. You could do this 2 or 3 times and it would probably get a lot more accurate. You don't need to continue doing fillups in DashCommand, once it gets where you want it you could just drive it and not worry about monitoring everywhere you go.

Thanks, I'll try that. If I reset the fuel economy tab in the future, does that also reset any data entered into the fillup screen? I sometimes reset the fuel economy tab just before a trip to get my readings only for that trip. I assume if I reset that, any work/calibration I have done on the fillup screen will be reset?

[Weston@PPE]

Yes if you reset both the trip and fuel economy tabs, it should clear all of your fillup data as well.

[Luis Fernando]

How do I reset the fuel economy tab?

[Weston@PPE]

If you touch the tab a second time, a little menu opens up with a reset button and a back button (the curly one is reset).