I logged a run on ECUscan, and it showed 4-5 counts of knock between 6500-7700 rpms. The log showed timing between 17-19 degrees of timing in that region. This is where is should be on the high octane fuel map. My question is - isn't the ECU suppose to pull timing if it sees knock?? Is the 4-5 counts not "enough" to pull timing? Or is the ECU not fast enough to respond on that exact moment, and then retards the timing after it sees it??

 

look at your octane column, if its 100% its not pulling timing yet. but at 4-5 counts i know your close until it starts averaging between your high and low octane maps.... im sorry i dont know exactly when it starts

 

it should start pulling timing 1 degree for every 2 counts of knock i believe

 

no i know thats wrong.... theres a threshold where a few knocks will not pull timing at all..... it may be around 6 or 7... i forgot sorry

 

Theres no real answer, from what I know nobody has figured out the exact formula. Most people say to just stay under 5 counts. At 5 is when it starts degrading the octane flag. It does interpolate between the maps, so theres no way to tell how MUCH timing its pulling either. I try to keep it to 1's and 2's here and there if Im doing a very agressive map.

 

There are two ways that the ECU will pull timing. They are additive as far as I know:

1. Roughly 1* of timing will be pulled per 3 counts of knock.

I don't know if this is completely disassembled in the EVO ECU, but this is how it works in the DSM ECU and from every log that I have seen from my car and others, it seems to hold true for the EVO ECU as well.

2. Octane number.

The octane number will begin to decrement at 6 counts of knock and above. The amount that the octane flag decreases determines how much weight the low octane map receives. For example, if your timing in a particular load/RPM cell is 20* on the high map and 14* on the low map and your octane number is at 50% of max, or 128, then you will get 17*.

Think of the octane number as a long term knock trim. Think of the 1* per 3 knock count logic as a short term knock trim. Both of those corrections will get you your final timing numbers.


Eric

 

ah... so setting the maps the same is a way to cram timing down the throat of your engine, when it doesnt want to cooperate.

 

Yes and no. You take the long term correction out of the mix, but you will still get timing being pulled because of the knock.

Settings the maps the same just gets rid of the long term correction, so the short term correction, so to speak, always has to compensate. The short term logic is the faster acting correction anway, and I think it can correct up to about 36 knock counts, which would be about 12* of timing retard.


Eric

 

I commonly see 1 knock count flat line or retard timing.

 

I've seen erratic behavior with knock pulling timing. I've had a 2 count pull timing and also seen a count of 5 not pull timing. It probably has to do with the loads of other knock filters and knock recognition techniques which may or may not translate directly into a knock count. I don't know much about the how the Evo monitors knock, but I do know that there are a lot of tables and values related to it other than the basic knock count.

 

It would be good to see the data and your high octane ignition map for these examples. Every log that I have seen for myself and other cars where the ignition maps were provided, it was always 1* for 3 counts.

A lot of people just look at their logged timing and if it is climbing, they think timing isn't being pulled. Or some use calculated load instead of 2 byte load and think they are in the right cell, but they aren't. You have to remember that the timing is being subtracted from whatever value is in the ignition map for that RPM and load.

Eric

 

as stated above sometimes 2 , 4 or 6 counts of knock sum will do nothing, other times a 2 count will drop timing in a heart beat. I notice that the greater the load the more likely a low knock sum will affect timing.

 

Well maybe it has to do with the different sensors, arent there like 12 of them. Depends on the significance of the knock. If one sensor picks it up no biggie, if two or 3 then maybe it pulls timing. but the way I see it, who cares what the algorithm is to determine how many degrees of timing is pulled. any pulled is a bad thing so correct it. If you figure out exactly how much time is pulled and for what circumstance, woooptie doo! I really dont care!? just correct the problem eh!

 

My guess is it is pulling timing. If you get 17* at 6500 you would get way more than 19* at 7700. I dont know what your mods/tune are, but maybe you should be seeing 21 or so up there.

Also as you can see noone knows how timing pulling works for sure and i bet there's a lot more than just one algorithm for it in the ecu. See knock - fix it.