Quote:
Originally Posted by viper1982
Hello Scott, can you tell me what is the strategy of the ecu of the my99 in the detection of knocking, (In prodrive AE801) apart from lowering the bost level, does this take any other collection such as the delay of the ignition? I am asking you to find out if by overriding the original solenoid and using an MBC to hold the 15.65 psi out of the normal range set by the ECU can I be sure that the ignition advance will fall behind in a knock situation? Thank you
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The ECU strategy uses base timing plus an ignition advance map. The ignition advance map adds additional ignition advance to the base timing map based on knock detection which causes adjustments to be made to the ignition advance multiplier.
When the ECU is reset the Ignition Advance Multiplier also resets to what is considered by the original developers to be a safe starting point.
This has a maximum value which most tools read out as 16 (although some convert this to a value of 1).
The starting point for the ignition advance multipler after reset is 12 (or if converted 0.75).
What this means is the Ignition Advance map is multiplied by 0.75 after a reset upto a maximum multiplication factot of 1 for a car running no detonation/knocking.
Therefore if for instance you have a base ignition of 15 degrees at peak load and 5200rpm, plus an advance of map of 6 degrees you will have a total advance of 21 degrees at that given point.
But only if the Ignition Advance Multipler is set to max.
After a reset the same scenario will run 15 degrees plus 4.5, so 19.5 degrees in total. This will slowly increase to 21 after a few mid throttle and full throttle runs if no knocking is detected.
If knock is detected the ignition advance multiplier gets reduced which in turn reduces the overall ignition timing.
When sufficient knock is detected to reduce the ignition advance multiplier to 8 (or 0.5 of the total available) bost is restricted by the ECU stopping the operation of the boost control solenoid. The will restrict boost to approx half (on a standard tune) to 0.6 bar.
A good check if you are running alternative boost control is to check the ignition advance multiplier. If it's running 16 (which is how ECUExplorer reports it) then all is good and no knock has been detected. However I caveat that by saying this mat not totally rule out knock.
The ECU only listens for knock between certain rpm ranges, for example 3000rpm - 5600rpm, therefore if you run a flat boost curve instead of the OEM tapering curve and its causing detonation at high rpm the ECU will not detect or adjust for it.
If your sensible with boost at high rpm, it should be pretty safe.
In all the live tuning I have done I have never head significant knock right at the top. The hotspot is 4800-5200rpm which is where most timing has to be pulled, this is well within most Subaru ECU listening zones although not on the 2008 STi hatch which may aswell be deaf.