jcsbanks

If knocksum is greater than 6 the following is added to the raw value of "AFRmap" which is the raw byte that has been interpolated from your fuel maps:

(Knocksum-6)*160/256

Result is limited to a maximum which is looked up from a coolant temperature map (all the values in it are D9, 217 or AFR 8.67).

The coolant temperature based maximum rich AFR, the threshold of 6, and the multiplier of 160 are all adjustable if you really wanted to.

Practical result is that if you have 11.0 (171 raw AFRmap) in your fuel map and you have a knocksum of 10, then you will end up with:

(10-6)*160/256=2 (logical shifted to divide by 256 so rounded down)

So AFRmap will become 173 or 10.9.

Knocksum of 36:

(36-6)*160/256=18, so AFRmap will become 189 or 10.0.

For this to operate your octane number would also be dropping to push you towards the low octane maps. Nice to know the ECU can throw in 10% extra fuel within 6 ignition events or 3 engine revolutions if it has to though. In extremis this should help to mitigate the rising EGT that retarding the ignition very rapidly would also produce.

It is a pretty small effect/non-existent in normal operation, not worth adjusting, but worth knowing about.

l2r99gst

iTrader: (2)

Thanks for the explanation and find, John. Just helps us understand the knock control even more.


Eric

C6C6CH3vo

iTrader: (9)

Thank you for using your abilities and contributing.

dan l

iTrader: (3)

Ewwwww. I want to zero that crap out!

justboosted02

iTrader: (31)

why? fix your falseknock with the tables and this wont be a problem unless you actually have knock.


i want my motor to do everything it can to combat knock as long as its actually knock

jcsbanks

dan l, I suspect this sort of thing is what saves motors when fuel pressure reg lines come off or fuel pumps get tired, didn't you have a story like this? DSM did it too. I think it is good, much quicker than the migration to low octane.

dan l

iTrader: (3)

Yeah, I lost a motor because I disabled the ability for the Ecu to pull timing with knock on my DSM. My intercooler broke so I ran with no intercooler and due to boost creep I couldn't run less than 24psi. I also didn't have any race gas, so I was stuck with 92 octane pump. Couple that with the fact that my fwd spins in third (closer to evo 4th) so I have to do pulls in 4th gear ( 70-140mph) I lost a motor. It was pig rich on the wideband (low 10's). I don't feel that extra fuel helps anything. In some cases it makes things worse. Timing pull saves the show. I did numerous pulls with timing pull enabled on the same setup minutes before. I thought the timing pull was causing the misfires I was chasing. A single 4th gear pull pushed the freeze plug out the back of the block with no timing pull. Numerous pulls with timing pull enabled and I didn't hurt the motor (it just misfired). To rub salt into wounds the misfires were not low ignition advance related, it was valve float, doh!

So, long story short. You can kill a motor easily running rich. Timing pull is what saves everything. Is this "fuel addition" easily disabled with a periphery code. I understand it is dangerous, however I'm prepping to put an evo ecu in my DSM because that is how configurable you guys have made it, especially since I can tailor the knock maps to my DSM

jcsbanks

The threshold of 6 could be changed to 36, so only knock sums over 36 (impossible as it is limited to 36) would enrich.

Mattjin

Sorry to be the fly in the ointment here, but dan_l, I tend to believe you lost your motor from inappropriate tuning coupled with some bad decisions. Its not because you ran without the knock retard. If you tuned to suit a certain setup, then change that setup (remove intercooler) and run on low grade fuel, and still give the motor a hard time... what can I say! Relying on knock control is a very bad thing to do. The motor has to knock first before it can react, so its better to tune to not have any knock in the first place and then it becomes reliable.

There are alot of motors that do respond to knock with fuel. The higher you go in compression I find the more likely a little fuel can help. Remember, the ecu is trying to do everything it can to save the motor. I would have thought 1 AF point richer is not far enough and would have thought they would go alot richer than that.

jcsbanks

Many of us have done silly stuff and learned from it. Like many I've done a ring land and head gasket from detonation during a top speed run on an ECU without knock control that seemed to be well setup for many thousands of miles, just without sustained top speed. I was monitoring knock sensor noise, but I think a single bad knock did the damage!

dan l

iTrader: (3)

Mattjin, I knew I was going to blow it up. I really didn't care. I even drove it 6 miles home on a 95F degree day with no freeze plug. I honestly didn't care.

Jscbanks, what location is this in the rom so that I can put it in my notes for the future.

nothere

iTrader: (23)

Just to add a bit.

I lost my engine a couple of months ago. My fault, I was flirting with too lean and got slapped.

I was also logging on a road course when it happened. I had not had any sign of knock (over 2 or 3 for quick hits) in several laps. There had been one incident coming off of a yellow flag where I got the 36 count which I figure was bogus. Never happened again under similar situations.

I've never touched the knock maps.

The net result, no knock, motor lost . My guess, pistons got too hot from lean under load.
What I am saying is: You can lose an engine without knocking.

There may have been other reasons too, I don't know.

jcsbanks

Evo 9: 13ae
Evo 8: 17ae

Both are word length (2 bytes), should be 6, change to 36 to disable.

Mattjin

So the above comments only add to the case of allowing enrichment to stay in place as part of knock control. That is what I am getting at, I am not trying to attack anyone.... well maybe a little for choosing to kill your motor :-) Not all knock is from too much timing. Some requires fuel to be added to get things under control. Especially if you start loosing fuel flow for whatever reason - pump, filter, blocked injectors, surging, etc... But primarily motors are lost through inexperience and bad decisions

Is is possible to make this control system run more enrichment on knock than it currently does?

jcsbanks

Yes, reduce the value of 6 so that fuel is added from a lower knock sum. If you want the multiplier, IIRC it is the word afterwards, stock at 160, higher values will add more enrichment.

The reason for this disassembly and the thread to report the results was really just to find out how much it was adding and when.