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Diablo knock and AFR

6436 Views 13 Replies 2 Participants Last post by  Ddaddy
So I am looking at my data for my Diablo Intune recording and I have a few questions. First question is on my "KNK ST RETARD" I got a Max of 4.5, is that bad? and I was wondering how to see my AFR. I have two files with the AFR logo beside them and one is titled "DESIRED FA CYL1 (AFR)" and the other is "OPEN LOOP FA (AFR)". Is either one of them what I should be looking at for my AFR because the "DESIRED FA CYL1" is reading a value of 14.77 and the "OPEN LOOP FA" is reading a value of 14.53. Also I was told by Diablo I can safely change my WOT fuel by 5% richer, does that sound safe to do with the above information? If anyone needs any other information just let me know.
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"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. :)
so basically it would be a really good idea for me to increase my WOT fuel 5% richer, right? I don't see how I am running lean when all I did was load the canned 93 Octane tune. I am using 93 Octane gas from Speedway so maybe it is the gasoline? I've heard some people talk bad about Speedway and others said they love it so I'm not sure if Speedway is a bad gas station or not.
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.
By this do you mean a genuine custom tune? I've thrown some Emails back in forth with Johan about getting a custom tune but I am not sure if it would be much better than the canned tune that is already on the Diablo.
P.S. I don't have very many performance mods right now and the few I have are basic. Volant CAI, Mid-muffler delete, Billet oil catch can (kinda performance), and the 93 Octane gas (I hope is true 93 Octane :frown2:)
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.
I guess I am just worried about screwing up my AFR. I just went out and re-tuned the Charger. I added 5% richer on the fuel WOT and it held the knock knk st down to 3 (was 4.5) on a 2-4 mile drive but it didn't seem to move the other AFR values that we discussed earlier. I am scared to go too in depth just because I don't want engine trouble but I don't know why those previous AFR numbers aren't dropping from the 14's...I am wondering if that is even my air/fuel ratio at all because I've never installed a wideband sensor that everyone seems to be suggesting to get.
Ok, deep 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 there's no risk of doing any harm. ;)
I will defiantly keep up to date on it. Lol I had to just step away and breath, I normally don't get too worked up but this is my first Charger and I LOVE my Hemi lol. I am just going to leave it where it is like you recommend and see how it plays out. So just wait a week and then hook the Diablo back up and run it for a bit and see what it is reading?
P.S. Thanks for the help! :grin2::beerchug:
Glad to help. Yes, just leave it alone for a week and then check again.
So I just drove around for about half an hour and here is the results.
KNK LT RETARD, Value = 0.0, Min = 0.0, Max = 0.0
KNK ST RETARD, Value = 0.0, Min = 0.0, Max = 2.5
So I guess that is a good sign? :grin2:
Yes Sir! It looks like you got it nailed with zero LT KR and minimal ST KR. :)
I'd like to get my ST KR to 0 as well =)
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