Fuel Temperature Density Correction

[Gelf VXR]

You don't find many forum posts regarding fuel temperature density correction.

Fuel density changes ~5.5% over a range of 50°C (, -10,1.0277, 0,1.01662, 10,1.00554, 20,0.99446, 30,0.98338, 40,0.9723)


I guess the trims cope adjusting fueling to account this difference, from season to season it would explain if trims are going positive in hot weather, negative in cold weather.

The injector flow modifier for IAT seems to be the candidate for making corrections for fuel temp, its generally set at 1 for all temps, but Ive seen the LS7 or LS9 with different values at high IAT, factor <1, it looks as thou reducing flow to compensate for less dense air, I thought MAF or GMVE would calibrate for this? So i think it must be to compensate for less dense fuel.

The IAT modifier is linear with change in fuel density as below, graph attached


T*___LS9_______Change in Fuel Density
40___0.986024__0.9723
50___0.971986__0.96122
60___0.961976__0.95014
70___0.95398___0.93906
80___0.947999__0.92798



Normally minimum IAT would be equal to ambient, or higher, so using the below values would compensate for change in fuel density <1 as fuel temps increase, density decreases, >1 as temps decrease, density increases. Fuel density is normally shown at 15°C which would be factor 1.

(, -40,1.06094, -30,1.04986, -20,1.03878, -10,1.0277, 0,1.01662, 10,1.00554, 20,0.99446, 30,0.98338, 40,0.9723, 50,0.96122, 60,0.95014, 70,0.93906, 80,0.92798, 90,0.9169, 100,0.90582, 110,0.89474, 120,0.88366)





Any thoughts, being done already?

[5.7ute]

Fuel temperature with a return-less system would be closer to ECT than IAT I would have thought. But it is a good question non the less.

[statesman]

Fuel temperature with a return-less system would be closer to ECT than IAT I would have thought.

I think you're right. My fuel system is return-less and I don't see any difference between winter and summer.

[Chevy366]

Is this for cold start enrichment after start up?
ECT, IAT and 1,2 or 3 Bar MAP

[Gelf VXR]

I'm curious to see if there is a modifier for fuel temp density, for all temperature conditions. Trying to get idea from old logs

When I'm looking at the log sat at idle OL SD, average Charge Temp 87°C, IAT 71°C, DYNAIR = 8.56 g/sec, 800RPM, WB EQR average 1.0002, stoich is AFR 14.7, average IPW 1.581ms.


8.56 g/sec divide by 14.7 = 0.5823 g/sec calculated fuel flow.


However, when i compare to my calc.pid for fuel flow using stock LS3 injector data

Inj Flow Base (VAC referenced) * IPW * 800 / 1500 = 0.6443 g/sec,


This why I'm thinking there isn't a modifier, the fuel flow g/sec calculates a lot less than expected, by a factor 0.904


If fuel density was referenced at 0°C rather than 15°C, a rise of 70°C would be a factor of .923. using density data i used for petroleum products.

It would support the idea no modifier is used.


More research required.


I'm also curious as how the temperature Bias for OL speed density is referenced when the MAF removed (or in my case disabled), the value is normally referenced from B0115, airflow from the MAF sensor. I had set my MAF tables also to 1g/sec for all Hz. So how accurate is DYNAIR in this case?

[5.7ute]

Where are you getting IPW from in your calcs?

[Gelf VXR]

where are you getting ipw from in your calcs?

gm.injpwb1/b2

[5.7ute]

Remember you need to remove the offsets for any calculations to work :-)

[Gelf VXR]

Ahh,

I looked up injector flow MAP correction at MAP ~37kPa/ VAC~64kPa & volts 14v = 0.8 ms, small pulse adjust around 1.5ms = -0.05ms

1.581 - 0.8 - (-0.05) = 0.831

5.67 * 0.831 * 800 / 15000 = 0.2513 g/sec

I did something wrong?


My calc.pid which was for fuel economy, it doesn't matter really, better a simple calc.pid for fuel flow from corrected airflow for economy :)

[Gelf VXR]

Just come across this tutorial from Swingtan, pages 7, 8 and 9 on IAT B1213 calibration :coool: