Ignition ECU logic

[ayau]

Running the standard Hondata E25 calibration. Trying to understand how the ECU logic works with respect to ignition timing table.

As you can see in the screenshot, the engine is currently at 6 degrees, 211% air charge, and 4.4k RPM. Based on those parameters, the ignition table shows that it should be at about 12 degrees. There's no indication of knock as shown in the logs. IATs also look pretty normal.

My question is, is the ignition table the maximum ignition the ECU is able to use in case it needs it? For example, if the torque table is requesting 480 tq, then the ECU's logic thinks it can achieve that with 6 degrees rather than 12 degrees. In other words, if I change the requesting torque to 500, would it increase the ignition to something around 10-11?

[Hondata]

The ECU does not change the ignition based on torque request.

I think at that rpm you are on the high cam and the table ignition value would be around 10 degrees. The difference could be VSA (can't tell just from a screen shot) or one of the other compensations.

[ayau]

Pull was done in 4th gear, so traction shouldn't been an issue. Added the TC.R sensor data to support that.

So is the ignition sensor data a 'calculated' number based on the various ignition tables? Just trying to understand the numbers on the table and actual timing the engine runs as shown in the logs.

I've also included the actual log file.

[Hondata]

The ignition advance datalog value is the actual ignition advance.

In the datalog I see 3rd gear and up to 4 degrees of traction control retard. Also there can be traction control retard which occurs the between datalog frames and therefore not shown in the datalog. But at 4400 rpm there is 4 degrees of TC retard.

[ayau]

I apologize but I just realized I uploaded the wrong datalog. Too many logs and easy to lose track. Here's the correct log. This one should be in 4th gear. No tc.retard that I can tell. Is it still possible that there's a small amount of slip that the frames aren't picking up, which could explain why it's only 6 degrees instead of 10? I didn't think the tires could slip in 4th.

[Hondata]

TC slip is 1% so it is not TC retard. In that case it is one of the compensations between the base ignition and final ignition value.

[ayau]

So just to make sure I understand this correctly.

The ECU looks at your throttle pedal position relative to current RPM. It then looks at the torque request table, for example, 480Nm. The ECU does a calculation to determine the amount of air/boost and timing it will need. Once it knows the air and timing values, it will supply the necessary fuel to hit the specified AF values.

What if you give the ECU an unreasonable torque request value like 600 and you're only using 91 octane? What will the ECU try to do?

Is this the correct understanding?

[Hondata]

The ECU looks up the target torque from the throttle/rpm table. It also has a maximum torque by rpm table and will limit the torque to that value.

From there is calculates the air charge necessary to achieve that torque. There also are limitations like pressure ratio and EGT which can alter the maximum air charge, and compensations like lambda & ignition timing to try and get the right final torque value.

Then the ECU will look at the air charge and use the VE tables to work out what manifold pressure it needs. It then uses the throttle and/or wastegate to get the right manifold pressure.

So if you target 1000 Nm then some other table will limit the air charge / manifold pressure.

[ayau]

So once it calculates the air charge necessary to achieve x torque, it uses the ignition table to apply the defined timing, correct?

So in other words, the torque request table is more like a torque limiting table. You set the torque request values high enough so that you can add timing to try to hit that requested torque? It will most likely not hit that requested torque because you generally don’t want that to be the limiting factor when tuning?

[ayau]

What have you guys been seeing as the "sweet spot" in terms of timing vs boost on ethanol and factory fuel pump?

Just playing around with the air charge limit numbers. I've reduced the airC limits pretty significantly in order to force the ecu to use the higher timing values. This is on E30 fuel. The car feels a bit more "NA", which is to be expected with more timing. Here's a 4th gear pull log.