Fuel temperature correction help

[aceswerling]

I'm looking to enable the Fuel Temperature Correction feature. I'd like to check my logic with somebody who's done this before.

To start, I installed a GM flex fuel sensor and my MS3 is correctly receiving fuel temperature from it. Then I enabled Temperature Correction on the Fuel Pump and Pressure Control page but saw no correction going on. I went a little deeper and the next step seems to be tweaking the Temperature Adjustment (Primary Fuel) table to instruct the ECU how to correct. I can't find anything online about how this should be set so I started looking for information about how gasoline volume changes with temperature.

I found a link at http://datagenetics.com/blog/april32015/ saying gasoline expands about 1% for every 19*F change and ethanol expands about 18% more than that. I also found a table with gasoline correction factors based on an index of 60*F.


Based on the different volumes of gasoline and ethanol, I figured I should to determine the density change based on 90% gasoline and 10% ethanol based on the fuel sold here in Washington. Then I found a chart at https://www.ic.gc.ca/eic/site/mc-mc.nsf ... 00129.html that shows only ~.1% lower density for 90:10 gasohol. I figure that's not worth worrying about.

As a place to start, I'm thinking I need to reflect the gasoline volume correction numbers from the first chart in the the Megasquirt's Temperature Adjustment table. Is that right?

I didn't do my tuning at 60*F, and while I don't know what the fuel temperature was because I didn't have that sensor installed, I'm guessing it was between 75 and 85 degrees. That means my index, i.e. my zero point, would need to be different than the chart.

I'm thinking about indexing to 80*, which should mean shifting that table so 80* is my zero point, my 100 would equal the table's 80, and so on. Once the Megasquirt is correcting, I can experimentally observe AFRs and EGO correction to see how close I am. I can then adjust up/down based on what the engine wants.

What do you all think?

[aceswerling]

FYI, I took some of the online data and made my best guess about how the correction should go. In my research, I found the API has tables for these corrections but I couldn't find them online. I used the numbers from the Canadian website and figured 10*C was close to 20*F.

In the end, I estimated a 1.2 - 1.3% change for every 20*F as shown in


I'm sure that's not totally accurate but it seems to be doing OK based on my observations. My AFRs are a lot more stable and I'm seeing less EGO correction between hot and cold conditions. I'm thinking about calling up BP or Chevron to see if they'll tell me the specific gravity of gasoline in Washington, and better yet, give me the exact numbers for this table. But if not, these ones seem like they'll work well enough.

I'm also thinking about setting the table to its regular index point at 60*F and autotuning fuel again.

[aceswerling]

In case somebody needs this information in the future....

BP says that the specific gravity of Washington fuel will vary between summer and winter but will average around .72 to .73. It will go as low as .69 in the summer but they said .72 was a good target. This means Washington fuel is similar to the California fuel in the table I posted earlier.

[Speedy_G]

thanks for sharing.
Good to know.

I'm planning to use this feature one day, too.
And maybe someday also a air humidity correction.

[Xenocide101]

Anybody have the picture that the aceswerling posted? The link is broken.

I ended up finding the chart that has the density/volume expansion/contraction of gasoline as well as the different mixtures of ethanol in 10% increments up to 90%.

Here titled: Volume correction factors—gasoline and gasoline ethanol blends
https://www.ic.gc.ca/eic/site/mc-mc.nsf ... 00129.html

I put the inverse of that (because this is for price adjustment) into Tunerstudio getting a line that increases to the right. a positive slope. and it crosses the y-axis at 59F or 15C.
I used this formula in Excel to get a percent: =((0.00125*(TempC-15))*100)
I used this formula in Excel to get Celsius: =(TempF-32)*5/9

My thinking is that because fuel becomes less dense as it heats up, it needs a tiny bit more to compensate for its loss of density and therefore Energy Density. I've heard old race car guys say that whey used to add dry ice to their fuel tank in the summer to get more performance. Performance because it's making the fuel more dense and not allowing it to heat up.

After thinking about it, I don't think it matters where that line crosses as long as it crosses somewhere. ideally at the temp that it was tuned at. Right?
The equation can be adjusted by changing the 15 into the fuel TempC it was tuned at.

This is what i put into TunerStudio for pure gasoline sans Ethanol.

-6.875 -4.097222222 -1.875 0 2.152777778 3.888888889 5.625 7.013888889 9.097222222 11.18055556
-40 0 32 59 90 115 140 160 190 220

You should be able to copy and paste this directly in TunerStudio.
Anybody out there using this successfully?

Thanks Guys!

[theturbodog]

After thinking about it, I don't think it matters where that line crosses as long as it crosses somewhere.

Just as a data point...

I believe 125 F is a(or the) standard for testing injector flow. I've had a number of sets of injectors where the flow data was all at 43.5psi and 125 degrees F.