John, thanks for sussing this out.
Might be a good idea to doctor a little more enrichment into a race engine as a safety factor.
Maybe also on first time build-ups on the dyno, when things that can go wrong, find a way of doing so.

 

Nice find John, 17ae works on the E7 Roms too by looks of things.

 

Would reducing the point where enrichment happens or increasing the enrichment amount potentially reduce the effectiveness of the low octane maps?

I know a lot of guys make the low and high octane maps equal, but I'd personally prefer the high octane maps to take care of the motor 95% of the time. But if you did get a bad tank of gas, the low octane map would come in and keeps things conservative until you get some good gas back in it.

It seems like if you lower the point where enrichment happens, it may prevent the detonation just enough temporarily to keep it from triggering the octane update?

 

That single episode occured during intense lateral g's under moderate acceleration at 20 psi too.

 

Seems similar to the setup on my Evo 3 John so I assume it's similar throughout the Evo range. Mine actually enriches based on both the octane flag value and the knocksum value so it will do a longer term adjustment as well as the instantaneous values.

Andy

 

Does it actually enrich based on the octane flag or just interpolate towards the low octane maps?

 

So with the example in the first post with a KS of 10 you are getting 0.1 increase in AFR. Usually when you have a fuel system failure like this: clogged fuel filter, things are much worse. The stock system can't even add a full point of AFR let alone the 2+ afr it would need to get things even close to normal but still "dangerous". Not only that but you can see that some (even most) cars that go lean don't detonate.

Another example is a friends FPR line that got a crack in it. Car went lean, very lean. It was like mid 13's lean but not knocking thaaaaat bad, about enough for the stock system to add 0.2 AFR.

So if you want to add fuel with knock, fine, but crank it up a LOT! However realize that pulling timing is a much better way to deal with detonation.

Hope your not angry at my comments, just trying to help the masses. I know you know what your doing, just wanted to clarify for the average joe.

 

Hi John,
Checked through my disassembly last night and you are correct, it interpolates between the high/low octane maps on the octane flag but it also applies a correction based on the knocksum value.

It does the same on the timing as well, interpolates between hi/lo based on octane and pulls timing based on the knocksum value.

Andy

 

Nah, I am not angry at all, we are all friends here :-) I am just trying to point things out to prevent people making the same mistakes in future.

If your knock is initiated because of a lean condition, such as a pump or filter problem, you will tend to see this begin at high injector duty conditions (fuel flow), usually WOT at high rpm. If the engine begins knocking at that condition it will keep doing so after you change gears and go WOT again. If you can help "cool" combustion by adding extra fuel it can help prevent the next leanout from being too extreme on knock for the next WOT cycle. It is why getting control of this is very important. if you clog a filter enough to have the lower rpm regions run lean, you definitely should be able to feel something is wrong and stop going WOT.

Mitsu obviously decided on values that are suitable for a stock standard street car have to meet emissions standards under all conditions, but if we are running a dedicated and modified track car we may need this system to deliver ALOT more fuel when it is needed, exactly like merlin.oz said.

But I agree that timing is the better solution, but not the only one and the more control we have for the tuner, the better we will all be. Awesome work finding this.

 

Cutting boost to 12psi on a road race car (for drivers that don't like to look at gauges) should save a stock compression motor no matter how lean it goes. The problem is that you would have to have the ecu log the wideband and load and kill the party if load is >200 and afr >13 for example. If the fuel system has already failed (clogged filter etc...) you can't really add fuel so pulling timing (which is already done) and then pulling out all the boost would be the best option.