Zero Pedal Torque Values typically negative in log?

[TriPinTaZ]

I'm tuning a C7 Corvette M7 and the idle is slow to return to normal but only when cold. Driver Demand is not touched in this area. Idle Virtual Torque is also stock. I think it may have to do with Speed Control Reserve. If the Zero Pedal Torque is typically a negative number, would this indicate the Speed Control Reserve should be lowered? I'm going to give it a test later but was wondering if anyone has encountered this before.


Log attached with Zero Pedal Torque PID being captured

16-new.hpl

[TriPinTaZ]

Actually now I'm thinking I need to lower my Idle External Load table. I'll report back.

[Ghostnotes]

You get it figured? My manual idles like a top now. In fact for me, idle/ coastdown was the hardest part.

[TriPinTaZ]

I haven't determined if I need to change these tables yet. I'm working on slightly lowering the Virtual Torque in the idle and low throttle input areas at lower RPM's first. Since the mods have slowed down the velocity of air coming in at low speeds to an even lower amount and then I increased the MAF for fueling which is causing Max Torque to go up. So it is not calibrated correctly at low speeds anymore. Once I have this dialed it I will see how the idle behaves.

[Ghostnotes]

I could not even idle at the right speed until I got the MAF right. After I did, my timing came up, my throttle closed a little more and my torque adjustments actually started working. I fought torque for a week until I threw my hands up and adjusted my MAF. I cant remember exactly which tables(at work right now) have to match you idle speed according to the coolant temp, but if they are off it just adds to the error.

[TriPinTaZ]

The MAF is good. It drives fine and idles with 13-15 degrees of timing. The only thing is when cold and it is in cat warmup mode, any throttle input raises the RPM's more than desired. Once the car is warm, the issue is gone.

[TriPinTaZ]

The Idle External Load table behaves like an airflow table but instead of grams of air like the old days, its measured by torque. Being that it is torque it can be affected by other things that are involved in the final engine torque calculation. Essentially though, it is a torque based "airflow" table and the Idle Torque Limit Offset is the most amount of torque the ECU can try to add or remove to the values in the External Load table to meet the Idle Target. Idle Target includes all Zero Pedal Torque requests (AKA, when your foot is not on the gas, including coast down). To reach a torque value the ECU can use throttle angle and spark.

Anyhow, by adjusting my Virtual Torque tables it has changed the idle behavior slightly for the better. Now I need to wait until a cold start scenario and log the behavior before I can determine if I need to adjust the External Load table.

[Ghostnotes]

I had to lower offset to about 85. I started at 100 with the cam I have, going past that made it worse. I will take a look tonight at my tables. But to get mine stable at idle and coastdown there were 3 tables I dealt with. I have to have my software to remember exactly which . I never did touch the torque tables during this. It was almost 80* outside when I dialed it in. It was 32 this morning and fired right up. This was before I installed the blower, but it has a big cam in it, not sure if you do or not. I might have added 3*of timing but I think that was after the blower.

[sevinn]

I think you found your answer already but I only see big negative numbers if virtual torque is too high for ext load.

Also since we're on the topic, pay attention to what's happening to negative numbers if you're trying to "reduce" virtual by a percentage instead of subtracting a number from the tables.

[TriPinTaZ]

I think you found your answer already but I only see big negative numbers if virtual torque is too high for ext load.

Also since we're on the topic, pay attention to what's happening to negative numbers if you're trying to "reduce" virtual by a percentage instead of subtracting a number from the tables.

I always manually fix the negative number sections if I happen to adjust this part of the Torque Tables. After this mornings logs the cold idle behaved better with my VT changes. I still think the External Load tables needs to be reduced. When I log Zero Pedal Torque against this table, I see a lot of -40 to -50 values especially above 1200 RPMs. I assume this is the ECU trying to reduce torque by that amount?

[sevinn]

I always manually fix the negative number sections if I happen to adjust this part of the Torque Tables. After this mornings logs the cold idle behaved better with my VT changes. I still think the External Load tables needs to be reduced. When I log Zero Pedal Torque against this table, I see a lot of -40 to -50 values especially above 1200 RPMs. I assume this is the ECU trying to reduce torque by that amount?

Sounds good, I've just seen lots of tunes where people are trying to reduce something by 20% and end up increasing the negative values because math

[Ben Charles]

Yep!! If they pay attention when doing it, the negative values will turn “RED” meaning a higher Tq value when in fact they should turn light blue for a lower value

[STL_G8GT]

I always manually fix the negative number sections if I happen to adjust this part of the Torque Tables. After this mornings logs the cold idle behaved better with my VT changes. I still think the External Load tables needs to be reduced. When I log Zero Pedal Torque against this table, I see a lot of -40 to -50 values especially above 1200 RPMs. I assume this is the ECU trying to reduce torque by that amount?

Interesting question here...

To clarify - is the zero pedal engine torque parameter shown in the scanner the adjustment the ecu is trying to make, or is the actual value the ecu is showing for the idle external load?

Example: The scanner shows 118. Is that 118 OVER the limit set in the idle external load table (inclusive of the limit offset or not?), or is that 118 idle external load?

[TriPinTaZ]

The value the scanner outputs from my understanding is the actual. 118 is a positive request so the ECU is using the Idle External Load table value for that area PLUS the Limit Offset. The ECU can add or remove the amount of torque specified by the Limit Offset in addition to what the External Load Table has.