Gen3 Idle Control with low vacuum

[Quicksand Jesus]

I am working on a 2019 Gen3 with a large cam, VCT lockout, and more. My question pertains to my ignorance of how the idle control systems REALLY work on the platform. This car in particular has much lower vacuum than a factory engine. It holds about -6 psi at 850RPM, which makes the car idle at a much higher "load" point in the torque reserve table. I've been struggling with this for quite some time, by "bending" the torque reserve at certain load points (.2 - .35) I can "force it" but it causes other problems in the torque calculations once it's off idle.

Is there a way to "offset" the torque idle? It appears that the idle torque reserve table may be what I want. Is there a good explanation of how this or other tables work or a flowchart on how the idle circuit functions on the platform with the available tables?

Thank you all for your time!

[engineermike]

I have not seen a good explanation so here goes the way I understand it?

The logic basically sets scheduled torque equal to pumping losses + torque reserve + accessory drive losses. Throttle is determined by: the torque-to-load table (for that mapped point and rpm) determines the needed load -> airflow which then determines the throttle angle (sd and tb models to used). Since the reserve torque is not actually consumed, this supplies more air than the engine needs for that idle speed. The timing is then used by the logic in the retard direction to pull down and fine tune the idle speed.

CSER is another degree of complication and involves supplying much more air and much less timing.

So in your case if you want to do it the right way, I believe the pumping loss model is what is likely out of whack since your vacuum is low and probably not accurately modeled. If it were me, I think Id start by playing with the slope of the pumping loss model and see where that gets you. You might even be able to steal it from the cobra jet cal.

If anyone has another explanation Id like to hear it.

[Quicksand Jesus]

I appreciate your reply, and I know our correspondence takes time.

I will be very open; I've never modified the pumping loss model. Is there any documentation on what it "should" actually do? In my decades of trial and error, I have tried not to change too many parameters to avoid the domino effect. This particular setup seems to want to fight to the end. I can play around with it.

Based on what you said and what I think, the torque reserve could help.

[engineermike]

As I understand it, this is what they’re modeling:

https://www.researchgate.net/profile...gine-speed.png

There are several coefficients in the tune but of course we can’t see the actual equation used. I came up with some derivation that maybe correct and matches the picture linked above. As you can see, the manifold vacuum has the most influence at idle. Iirc there is one coefficient for manifold vacuum so it’s not that hard to try higher and lower values to see how it affects the idle throttle angle.

Another thing that is likely affecting your idle is the SD model. The result of the model is manifold vacuum, which is next used to determine how much to open the throttle blade. You could try commanding different mapped points at idle to see if any works better than the others and that will be a clue.