Help with tuning out KNK

[DarthMuffin]

Hello, I just bought and installed my Diablo Predator tuner and could use some help tuning out some knock retard I'm getting with it.

I have an '08 Magnum SRT8. Stock except for a 180 t-stat (actually runs about 186-188) and a K&N stock replacement air filter (not the CAI, just a K&N filter that goes into the stock box). I'm running Exxon (aka Mobil) 92 octane gas, which is the only one on Diablo's "recommended" list around here. I don’t have an oil catch can and am unlikely to until at least spring (moving to a new city, have no garage, most tools are currently packed up until the house is finished being built).

I've downloaded the most recent tune and first loaded the 91 Octane performance tune and got a lot of knock (like 12 deg), so I went to the 91 CAI tune. Now I’m getting a KNK LT RETARD of 3.5 and an ST of 8. The knock seems to be happening at WOT, and throughout the RPM range. If it matters, I have also adjusted the fan turn-on points to what has been recommended for my 180 t-stat. So, my questions are:

1) Was going to the 91CAI tune the right move, or should I go back to the plain 91?
2) What steps do you recommend I take to get rid of this knock retard?
3) In WA state, by law, they only sell “oxygenatedâ€

[Quick]

That's some serious knock. First try a different gas station and add a healthy dose of fuel in modify parameters. The difference in the CAI tune and the non-CAI tune is more fuel in the CAI tune. Go into Modify Parameters and try adding 6%, 10%, 10% (that's low rpm range, mid rpm range, top rpm range) and see what that does. If the knock goes completely away then you might try backing it off a little at a time in each range until it just comes back after the shift points. I think what you want to see is NO long term knock retard and maybe up to 3* of knock retard momentarily right at or immediately after a shift.

If adding 6% 10% and 10% doesn't do it, add some more. Maybe another 5% in the ranges where you're still seeing constant knock retard. If that still doesn't do it then try pulling (retarding) a degree or two of timing in the rpm ranges that need it.

That's a lot of knock you got there. You might want to refrain from racing until you get this sorted out.

[mikel]

Yes, try different brand of fuel first!

[DarthMuffin]

Last week when I installed it I had 1/4 tank of Chevron 92 and got the 12 degrees of knock retard. I then topped up with Shell 92 and installed the 91 CAI tune and got the above results. I most recently filled up with a full tank of Exxon and retested to get the same knock retard results before posting here. So yes, I have tried 3 different brands of gas.

I will try adding 6/10/10% tonight and see how it does.

[SRT8Tech]

One more thing, let then car adapt a little before doing some logs for knock. I saw a loss of 2-3 degrees of knock go away after I drove the car for several days. Dont just load the tune and go do the logs. If you still have a ton 12*!!!!!! of KNOCK then something is a miss. I saw 6* of KNOCK on the new 91cai tune today iin the heat. Im going to drive it to work for a couple of days and see if it gets better. Most of the time it does. Only tune so far that has not gotten me any knock, over 3 AT THE MOST in VERY harsh conditions is my CMR tune. Then again my CMR tune is commanding wayyy less timing compared to the DS tunes. DAMN CRAPPY fuel I have. But in the long run the less timing is getting me better WHP and WTQ. Its the fuel PERIOD!!! And a catch can will help a degree or 2 of KNK. I can say that the low end power is noticeable in the new 9r08 tunes. Good job on that DS!!!!!

[Quick]

It really doesn't take much time to adapt to physical changes like adding a CAI (which would change the amount of air a bit in all modes of operation). The long term fuel adaptives move in moments. It will have adapted before you can move to where you can floor it. It's possible the TCM adaptives take longer but we're not worried about shifting.

Besides, the Predator only allows you to make changes to the PE table which only effects the amount of fuel added in WOT, open loop mode operation. You are not changing anything that would change closed loop operation. In open loop mode there is no adaptation going on. So the entire effect of adding or removing fuel (or timing) with the predator will be instantaneous.

[DarthMuffin]

I did another logging session tonight after the 6/10/10% fuel addition. LT KNK is about the same (1.5 on two runs, 2.0 on the third), but now it's only happening right after takeoff and at high RPM (one of those was while shifting too, which I understand is somewhat normal). I'm going to try 10/10/12% added fuel tomorrow unless anyone has a better idea. If that doesn't do it, then maybe I'll pull a degree of timing.

Thanks for the help so far. I had really hoped this would be much more "plug and play" than it has been...

[Quick]

I had really hoped this would be much more "plug and play" than it has been...

It is for most everybody. You are an exception. Some people see knock with the canned tunes that they adjust for and a couple have seen LT knock retard but for the majority it's just load and go.

[dcram71]

So is 2.5 ~ 5.5 ST KNK for a brief blip at WOT normal (more or less) on a CMR tunes 2008 5.7L?

[SRT8Tech]

I would say yes. Tip in knock and a little knock on shifts is normal. I just did several runs with the new tunes on the dyno and these tunes are pretty interesting. DS did a good job on these tunes. There is some initeresting changes in these 9r08 tunes. . Most I saw on ST with the 9r08 93cai tune knock was 6* of KNK on a very hot engine. It was tip in knock and tapered off quick. My CMR tune made a tat bit more than the 93cai, the 91cai made less than the 93cai but they were all close. I can say this, when it gets a little more cold out and less humidity here in hot as muggy Florida this 93cai tune is going to freakin come alive!!!!!! I can see there has been a shit load of work going into these DS tunes. Once again, good job DS!!!!!!!! By the way, this was all done with an unmodified 9r08 93cai tune. No timing or fuel changes were done with the CMR software. It definately is better than the 9r04 version. And absolutely the best advice out there is USE THE BEST FUEL YOU CAN FIND to take advantage of the tunes.

[DarthMuffin]

Grr... I'm losing ground now!

I went to 10/11.5/13% extra fuel and it's now knocking MORE. I got 3.5 LT and 6 ST tonight, maybe a degree throughout the runs but the worst at tip-in. Same gas, same weather. I don't get it.

I guess I'l try retarding the timing a degree and see what happens now.

[Quick]

I REALLY hate to mention false knock since everybody jumps on that and it's *RARELY* ever false knock. Call your service advisor. Tell him you've been using a OBD II scanner and you're seeing a lot of Knock Retard and you'd like to have your knock sensors checked and see if they'll do that? At least they can make sure they're torqued on there correctly. I very much doubt this has anything to do with it but it wouldn't hurt to have it checked if they'll do it under warranty. If you do take it in don't forget to restore your Original Tune first.

What is the timing? (log spark cyl_1)

Brings up another thing. Have you tried logging your stock tune?

[DarthMuffin]

No post for a while because I wanted to run through another tank of gas before testing again. I'm on the only available major brand I haven't tried (Conoco), and made sure it wasn't 10% ethanol like a lot of the stations around here.

I ran again with 8/10/10% additional fuel and got an LT of 5 and and ST of 8.5.

Then I went back to the stock tune and did another run. This time I got an LT of 1.5 and ST of 6.5. Is that enough that I should be talking to the dealer?

I've also ordered a catch can but it will be a few weeks. I'd like to get this straightened out within the first 30 days of ownership so I can return the Diabo if it doesn't work out.

[Quick]

Then I went back to the stock tune and did another run. This time I got an LT of 1.5 and ST of 6.5. Is that enough that I should be talking to the dealer?

Yes. Something's wrong. You should be seeing spikes of up to 4 or maybe 5 ST when lugging the engine or at shift points. It should recover to 0 very quickly. You should not be seeing any LT knock retard.

Try one more thing while you're waiting for your dealer visit. I think the Predator will log the knock sensor voltage? Should be a parameter for sensor 1 and sensor 2. (You have 2 knock sensors, 1 bolted to each side of the block just below the exhaust manifold). I think it would be unlikely for both of them to be whacked or torqued on there incorrectly. Log ST, LT and both knock sensor voltages. See if you can correlate voltage rises to the leading edge of knock retard. If you see a large difference from one side to the other then the implication is that the problem might be local to one of the sensors or it might be a problem with one of the cylinders/valve springs/etc. I'd think best case would be if it's just one of the sensors loose or bad (although I've never heard anyone mention a bad knock sensor yet). Worse if it's a real problem with one or two cylinders but if it is then it's still running so getting it fixed as soon as possible would be better. If it's both then... I dunno. I'll see if I can find a log of my stock knock retard . If I do I'll edit it in here.

[DarthMuffin]

Fortunately I did log the knock sensor voltage, at least on a few of the runs. I just spent a while looking at the data, and I do not see any direct correlation between voltage and knock retard. I did notice that knock sensor one always reads a bit higher than sensor two, but in general they seem to both be agreeing on their voltage trends.

I'll call the dealer tomorrow and see what they can do. Thanks for the help so far.