Boost limits, DAM and feedback knock

[KornShaDoW097]

Are boost limits only for 3rd Gear? my 2nd gear never hits the target boost is why I ask.


I just put in colder plugs and now my DAM is always 16 even with my advancing which used to show up as 7-9 DAM, but I have "Feedback knock" but no fine knock or knock active switch. Is it safe to continue advancing my ignition?

Where does the feedback knock come from? Maybe my sensitivity is just too low?


thanks

[Bill@COBB]

Are boost limits only for 3rd Gear? my 2nd gear never hits the target boost is why I ask.


I just put in colder plugs and now my DAM is always 16 even with my advancing which used to show up as 7-9 DAM, but I have "Feedback knock" but no fine knock or knock active switch. Is it safe to continue advancing my ignition?

Where does the feedback knock come from? Maybe my sensitivity is just too low?


thanks

Hi there. The boost limits are for any gear - you are just more likely to overboost in higher gears.

The engine control unit (ECU) has 4 different means to respond to knock:
1. Do nothing - if it is a low load/RPM, it is likely false knock and the ECU will ignore it.
2. Drop the DAM - if conditions dictate that the DAM is to change (generally after extreme fine knock learning), it will in response to a knock event. Note: the DAM will be reset to an initial value upon map reflash, ECU reset or battery disconnect.
3. Drop the fine knock learning in the current load/RPM cell - if conditions dictate that fine knock learning is active (generally steady load, etc.), it will drop the current cell upon knock event.
4. Enable feedback knock correction - this is the default correction if #2 and #3 do not apply.

The "Knock Active" switch will change everytime you see #2-#4 responses but it very quickly goes back to "off" after the event which means you will miss it entirely a lot of times.

Whether a knock response is problematic or not depends on when (what load) and under what conditions (throttle change, etc.) it occurs. Corrections at low load or when mashing the throttle are generally normal.

[KornShaDoW097]

I see. I was tuning for 2nd and noticed overboosting so now im tuning based on 3rd to correct/prevent this.
I'm aware that the ecu resets upon reflash (I do a reflash everytime to start fresh and make sure the DAM is right)

I've never seen the knock active switch go on in all the 20+ datalogs I've done so far (I'd of thought I'd of seen it at least once)

The thing is, the DAM is at 16 now that I put in new spark plugs (one step colder to compensate for higher boost and power range) and it seems to have fixed my low DAM numbers (prior to the plugs it hit as low as 6 DAM), It may have been hotspots caused by too much heat.


My question is this, now that my DAM is at 16 again which means (its safe to advance ignition), can I do so while taking into account that my feedback knock is "-4.22" 3k-5k RPM? (it gets down to -2 after 4K RPM), because if I advance and the ECU just counteracts the changes by using a feedback knock ignition correction, I'm not exactly going anywhere...(I'm assuming feedback knock is an ignition related control)

Also, Generally speaking, should I ever ignore the feedback knock values and what values are considered to be high?

the DAM being 16 has been this way for about 30-50 miles now of WOT test runs and mixed driving so I've been pushing it with no degrading of the DAM value.

Is fine knock learning something that can only be done via a laptop with the accessport? (I'm used to using my access tuner and desktop after a datalog, but in my datalogs its always "0".)

thanks

Jonathan

[Bill@COBB]

I see. I was tuning for 2nd and noticed overboosting so now im tuning based on 3rd to correct/prevent this.
I'm aware that the ecu resets upon reflash (I do a reflash everytime to start fresh and make sure the DAM is right)

I've never seen the knock active switch go on in all the 20+ datalogs I've done so far (I'd of thought I'd of seen it at least once)

The thing is, the DAM is at 16 now that I put in new spark plugs (one step colder to compensate for higher boost and power range) and it seems to have fixed my low DAM numbers (prior to the plugs it hit as low as 6 DAM), It may have been hotspots caused by too much heat.


My question is this, now that my DAM is at 16 again which means (its safe to advance ignition), can I do so while taking into account that my feedback knock is "-4.22" 3k-5k RPM? (it gets down to -2 after 4K RPM), because if I advance and the ECU just counteracts the changes by using a feedback knock ignition correction, I'm not exactly going anywhere...(I'm assuming feedback knock is an ignition related control)

Also, Generally speaking, should I ever ignore the feedback knock values and what values are considered to be high?

the DAM being 16 has been this way for about 30-50 miles now of WOT test runs and mixed driving so I've been pushing it with no degrading of the DAM value.

Is fine knock learning something that can only be done via a laptop with the accessport? (I'm used to using my access tuner and desktop after a datalog, but in my datalogs its always "0".)

thanks

Jonathan

The knock activity switch is really not very useful to log as although it is changing everytime there's a perceived knock event, it is very difficult to catch in the data log. The best way to determine a knock event is via the following:
1. Drop in DAM (not due to ECU reset)
2. Drop in current cell of fine knock learning. You can see the entire table by connecting to the ECU with ATR and viewing the "Fine Knock Learning" table.
3. Drop in feedback knock correction.

All above are knock events - the ECU just chooses to respond in different ways. You do not want to increase ign. timing adv. in an area where you notice knock events. You would want to try to determine the cause. Of course, at low load especially, you can have false knock. You can determine this if changes such as pulling timing/adding fuel have no effect on it. Just because the DAM is 16, doesn't mean you don't have knock. That is why you have to monitor fine knock learning and feedback knock as well.

[KornShaDoW097]

I checked the knock learning and everything is 0 in all tables. So there seems to be nothing indicating knock other than the feedback knock.
Could it just be noise?

I keep having the check engine light pop and the car experience a fuel cut feeling at 5k+ RPM. I'm lowering the WGDC everytime this happens but I haven't seen ANY over boosting after I fixed the over boosting happening in 3600RPM (which has nothing to do with 5k+) any other ideas?

[Bill@COBB]

I checked the knock learning and everything is 0 in all tables. So there seems to be nothing indicating knock other than the feedback knock.
Could it just be noise?

I keep having the check engine light pop and the car experience a fuel cut feeling at 5k+ RPM. I'm lowering the WGDC everytime this happens but I haven't seen ANY over boosting after I fixed the over boosting happening in 3600RPM (which has nothing to do with 5k+) any other ideas?

Keep in mind the knock learning table is cleared everytime you reflash a map to the ECU or reset the ECU via AP (or disconnect car's battery). At what load and under what conditions the reported knock occurs is important to determine. Reported knock at low load or knock that occurs when mashing the throttle (or lifting abruptly of the throttle), is more likely to be noise.

A boost limit fuel cut will give you a P0244 code. You want to check the code to verify that this is what is happening. Best thing to do is to get a log when the fuel cut happens so you can look at what boost is doing.

[KornShaDoW097]

I'm aware of that. I haven't reflashed or disconnected the battery, because I was attempting to find out what the knock learning table would tell me, but it was blank (nothing but zeros).

Yea, I'm doing that, I've adjusted the WGDC to a lower level and I tested it today at 75-80degrees with no knock, but once I got into <73 it had low level knocks. I added a ignition comp for IAT at a 68deg (-5.26 i believe, above load of 1.30, this should hit 73 deg with -4.06611, since i advanced the ign 2more degrees to test this and will know by my next log).

I believe the knock comes from the lower IAT, not because of the air temp but because my boost levels take advantage of the dense air and allow my goals to be hit (20PSI). I've added more fuel to help lower air temp inside the engine, hopefully this all helps and it reduces knock, otherwise I'll have to reduce boost and/or ignition.

I'm no longer overboosting as far as my datalogs today went, so I didn't experience the fuel cut, but I'll test again when I have a colder night.

I believed that colder plugs would help, but it seems that they did during hot IAT's but at lower IAT it seems to have made it worse(transfered the knock over to a lower engine heat range), but I may be wrong... do you know why this could be?

[Bill@COBB]

I'm aware of that. I haven't reflashed or disconnected the battery, because I was attempting to find out what the knock learning table would tell me, but it was blank (nothing but zeros).

Yea, I'm doing that, I've adjusted the WGDC to a lower level and I tested it today at 75-80degrees with no knock, but once I got into <73 it had low level knocks. I added a ignition comp for IAT at a 68deg (-5.26 i believe, above load of 1.30, this should hit 73 deg with -4.06611, since i advanced the ign 2more degrees to test this and will know by my next log).

I believe the knock comes from the lower IAT, not because of the air temp but because my boost levels take advantage of the dense air and allow my goals to be hit (20PSI). I've added more fuel to help lower air temp inside the engine, hopefully this all helps and it reduces knock, otherwise I'll have to reduce boost and/or ignition.

I'm no longer overboosting as far as my datalogs today went, so I didn't experience the fuel cut, but I'll test again when I have a colder night.

I believed that colder plugs would help, but it seems that they did during hot IAT's but at lower IAT it seems to have made it worse(transfered the knock over to a lower engine heat range), but I may be wrong... do you know why this could be?

You can try modifying the wastegate IAT comp so that you hit more consistent loads when outside temp is colder (and to reduce boost to avoid boost limit fuel cut).

[KornShaDoW097]

You can try modifying the wastegate IAT comp so that you hit more consistent loads when outside temp is colder (and to reduce boost to avoid boost limit fuel cut).

Thats true, that was my first approach but I've heard many people say that lower IAT/denser air is best for overall power vs the same PSI at a higher temp. For this reason I'm doing the opposite. I'm tuning the car for low temperatures and compensating slightly at higher temps, that way I can get max power when its cold and I can get a safe amount of power when its hotter out. Make sense?

Only thing I dont know, is how much boost should I expect at higher temps? should I attempt to be 2PSI lower than my max or higher or lower? That, I'm not sure of.

[Bill@COBB]

Thats true, that was my first approach but I've heard many people say that lower IAT/denser air is best for overall power vs the same PSI at a higher temp. For this reason I'm doing the opposite. I'm tuning the car for low temperatures and compensating slightly at higher temps, that way I can get max power when its cold and I can get a safe amount of power when its hotter out. Make sense?

Only thing I dont know, is how much boost should I expect at higher temps? should I attempt to be 2PSI lower than my max or higher or lower? That, I'm not sure of.

You don't have to boost higher to see improved performance at cold temps. 18 psi of boost with a temp of 50 degrees is going to be denser and make more potential power than 18 psi at 100 degrees temp. If you are trying to also allow the car to hit higher boost at colder temps, then you will need to look at the rest of the tune (esp. ignition timing) and experiment with it when it is cold out and see what works (including the level of boost).