I captured some logs today and observed a strange behavior with the Octane Flag reading. In some logs, my knock counts from 2500 – 6375 rpm was zero but the moment I hit higher rpm 6375+ my knock count jump all the way to 8. During this time frame I see my Octane Flag reading drop from 100 to 99’ish. I have not seen this behavior in my any of my prior log. I did fill up at Chevron with 91 octane this morning and perhaps bought some bad gas. Is this common sign of a bad tank of gas?

 

possibly? got any access to race gas?

 

There is a near by 76 station with 100 Octane. Since I filled up this morning I still have almost a full tank. So I have two options: 1st is to drop my boost and try to use up all this fuel and drive conservatively. Then fill up with another brand 91octane so I can finalize my 91 octane map. My 2nd option is to add 3.1 gallons in the existing bad tank to make 93 octane.

 

When the ECu detects knock for a long enought period of time, it reduces the 'octane flag' below 100. At this point, it'll start with a base fuel and timing that's richer and more retarded (hahahaha...... sorry, it's late).

I have a 91 map that I'm pretty happy with, and Naji posted up his map. Can compare if you want. I use shell by the way...

 

When the knock count gets to 6 the ECU will decrement the Octane flag, this is the proper operation for the unit. Whats your timing and load in the area of knock?

MB

 

nah dont waste racegas when u have so much 91.... just do some granny driving back and forth to work etc ... u wont have to touch the MBC. get your gas down to quarter of a tank, add 3 or 4 gallons... this will push your octane mix to high 90's... go for test runs and log!

 

How much boost are you running on 91 oct.? What are your AFRs and timing in the knock area? What gear was the knock (what boost were you at when it starting knocking)? For example some people just log in 3rd or 4th gear and see little to no knock and then do a pull in 5th and start seeing knock...Different load cells...

Anyway, most will need more info. to provide you with a more detailed response (IMHO).