Diablo knock and AFR

Ddaddy said:

"KNK ST RETARD" is the short term KR and should be ideally be 3 or below. 4.5 won't hurt the engine, but it will cause the PCM to pull timing to compensate (protect the engine) and you will lose power as a result. "KNK LT RETARD" should be zero when the car is properly tuned. In both cases, the car has knock sensors and will pull timing to protect the engine when it's detected. The only real detriment is loss of maximum power.

The advice to add more fuel is because knock is generally the result of running too lean which leads to detonation (knock). Again, it can't hurt the engine since it will protect itself.

"DESIRED FA CYL1" is the reading in closed loop operation when the PCM provides feedback based on actual data to adjust the fuel trim. "OPEN LOOP FA (AFR)" is what the car operates when at WOT when the system doesn't use actual data and simply runs on the programmed tables stored in the PCM.

For pure octane, the stoichiometric mixture is approximately 14.7:1. A stoichiometric mixture unfortunately burns very hot and can damage engine components if the engine is placed under high load at this fuel–air mixture. Due to the high temperatures at this mixture, detonation of the fuel–air mix shortly after maximum cylinder pressure is possible under high load (referred to as knocking or pinging). Detonation can cause serious engine damage as the uncontrolled burning of the fuel air mix can create very high pressures in the cylinder. As a consequence, stoichiometric mixtures are only used under light load conditions. For acceleration and high load conditions, a richer mixture (lower air–fuel ratio) is used to produce cooler combustion products and thereby prevent detonation and overheating of the cylinder head

In naturally aspirated engines powered by octane, maximum power is generally 12.5 to 13

Based on your readings of 14.77 closed loop and 14.53 open loop, you are running too lean and need to add more fuel to bring it down into the range of 12.5-13. The exact A/F that is best in your engine will be determined by "tuning" the fuel to get your ST and LT KR values into the desired range of not more than 3 for ST KR and 0 LT KR.

I hope this makes sense.

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Ddaddy said:

The advantage of custom tuning and why folks love the performance it gives is that it optimizes all of the parameters to get every bit of power out of the engine with the fuel you use.

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Ddaddy said:

Although a custom tune by a professional is generally the best option, you can do it mostly yourself using the same parameters I outlined above. the canned tune is just a general set of parameters that can be universally applied but they aren't tuned specifically for how your engine is behaving.

All someone like Johan does is read the data from the logs and make the same adjustments that I described to get the fuel trim and spark advance settings to an optimal point. They may also make some other minor adjustments to shift points and shift firmness to enhance the "feel" of the drivetrain to make the customer happy. Sometimes they also add throttle boost to make the pedal more responsive too.

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Ddaddy said:

Ok, deep breath...you are doing just fine. ST KR down to 3 is good.

Leave the 5% fuel addition for a while and ignore the A/F ratio for now. What you want to see is the LT KR drop down to zero after driving it for a while. It will take some time for the ST KR values to translate to the LT KR values. Give it a week and then post the numbers again. All you really care about right now is ST and LT knock retard to get it tuned well.

Remember, you aren't doing anything right now that is outside of the range of the PCM's ability to protect the engine...so there's no risk of doing any harm.

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Ddaddy said:

Glad to help. Yes, just leave it alone for a week and then check again.

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Ddaddy said:

Yes Sir! It looks like you got it nailed with zero LT KR and minimal ST KR.

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