by **GT_Rich** » Sun Feb 24, 2019 2:35 pm

I caught a couple decent weather days here so I've played around with transient fuel and also I think I have my lean IAC air condition sorted out (see other post).

At this point, I'm trying to understand the transient fuel parameters. As I gather it, the transient fuel amount is going to be the product of these three parameters:

Equilibrium Intake Surface Fuel Multiplier (AISFM)

Fuel Surface Multiplier vs RPM (FN313)

Equilibrium Intake Surface Fuel (FN1321)

If I compare ZXA5 with a stock Cobra (LLX3) tune, and do the math for any given load/rpm/ect, the numbers work out fairly close. It works out because generally speaking the multiplier is a magnitude smaller in ZXA5, but the intake fuel surface is a magnitude larger. This is especially true near 180 ECT.

For transient fuel, larger numbers will make acceleration fatter and deceleration leaner.

Now, for the time constant. As I understand it, this is the amount of time the calculated transient fuel is applied. For an acceleration condition, it is the product of these parameters:

Equilibrium Fuel Transfer Time Constant Multiplier (MTEFTC)

Fuel Mass Accel vs ECT (FN312S)

Transient Fuel Accel Time Constant (FN1322AL)

Transient Fuel Gain Startup (FN1323A)

And for the fuel gain startup, the top row is used once the timer is max'd out (100 or 120 seconds).

For the time constant, when I compare ZXA5 to LLX3, there is a magnitude of difference. With ZXA5 having roughly 10x the time constant for accel.

Have a made a poor assumption with the time constants or is this real?

I've played with things a bit and at this point I have the amount of fuel close. I made one adjustment to the time constant, going from .09 to .06. That helped, but I still have way too much time application and I'm quickly approaching zero.

The Fuel Mass Accel vs ECT is two magnitudes different. I don't quite understand how the two tunes could be so different or what this exactly is.

Any advice is appreciated. I'm still working from the ZXA5 tune at this point.