Help me diagnose this KR

[bluegoat06]

The car is a G8GT with Kooks 1 7/8 Mid lenght headers, hi flow cats, stock CB with mufflers and x pipe, and Rotofab CAI, Cali 91 Octane gas.

The KR at WOT past 5000rpm is driving me crazy , question is why this damn engine cannot take more than 18* at 5200rpm or 20* at 5600rpm. i have a tune that basically command 16-19* in the same area and of course KR is not an issue. once i up the timing, (16-19* seems fairly low), the KR starts.

I'm attaching a log from this morning, 3rd gear pull with a shift into 4th to observe the KR in the problematic cells. also the config file since i'm also logging KR per cylinder.

The timing is still low at 19-20*, fuel at about .84-.86 lambda, she shouldn't show KR, so what that hell is going with this heap ?

Car runs good with less timing, but again, 16-19* in those areas sounds fairly low.

[gn2beatu]

I did notice the MAF drop 10-12% right as it senses the knock retard, and you O2mv drop a tiny bit from .890 to .870

That would lead me to think if the MAF is dropping in hz, that your O2's would get richer not leaner. One thing that could cause them to go down in a case like that would be misfire. Maybe do another log and add the misfire by cylinder to see if thats the case, and then you will know what cylinder is causing it. It is on bank one, as bank two mv dont drop quite the way bank 1 does. Hope this gives you something to look at anyways and or a way to trace where its coming from.

If you do narrow it down to one cylinder, put a new plug in it and relog, if thats not it, then swap one thing at a time to another cylinder and then relog to see if it jumps cylinders. EX: wire, then injector.

[bluegoat06]

Thanks for the suggestion. I'll add the misfire per cyl pid's and total misfire to the scanner to check that route.

[IDRIVEAG8GT]

Looks false to me, like vibration induced. I run 19-21 degrees, with forced induction, on 93 octane. 10.8:1 Compression.

Check the mechanical factors around the knock sensors.

[bluegoat06]

Tested a 3rd WOT run this morning, slightly going up hill this time, and there are no missfires at WOT. Surprisingly, the KR was less this morning, even going up hill.

[bluegoat06]

Looks false to me, like vibration induced. I run 19-21 degrees, with forced induction, on 93 octane. 10.8:1 Compression.

Check the mechanical factors around the knock sensors.

Where are the knock sensors located ? Do you have a pic or diagram link i can check ?

[DSteck]

Are you sure it isn't just a bad tank of gas? I've had cars with 93 octane from QuikTrip that knock their ass off and timing ends up about 10* lower than it should. As soon as they get 93 octane from a good gas station (like Shell, BP, or Mobil), all the timing comes back no problem.

[bluegoat06]

I've tried different gas stations with the same results, another problem is that i can't find 93 at the pump around here, dang Southern Cali
I can mix 100 octane gas to come up with 93-94 octane,but 100 octane is around 10$/gallon.

I have no issues with E85 for example, i can bump the timing to 23-24* in the same areas without KR, but i don't understand why the engine would show KR with only 19* and 91 octane.

I've tried going super rich (.78 - .80 lambda) as a test, and the KR is still there.

[IDRIVEAG8GT]

Where are the knock sensors located ? Do you have a pic or diagram link i can check ?

Hehe, they're on the bottom (sides) of your block. The headers primary pipes run right by them.

[DSteck]

Try a slightly colder plug.

[bluegoat06]

Did that already, went from stockers to TR6, ran them for like 20k miles, and now i'm back to the stock heat range with TR5's.

Something i've noticed is that the KR is a lot less when the temp outside is cold like it was today today (50F), with cold IAT's (today at 55-58F IAT) i won't see those 3* KR, it was 1* max, same gas in the tank, in the afternoon with 70F+ (76-80IAT) outside, guaranteed 3* KR by 5200-5600rpm with the timing i currently have in the file i posted.

I can add timing to the IAT modifier and put it back to stock (I zeroed the 86-95F rows), but still, i can't believe this sucker won't take more than 18* at 5200rpm. it's pretty much a stock engine with little exhaust done. dang it.

[bluegoat06]

Hehe, they're on the bottom (sides) of your block. The headers primary pipes run right by them.

Silly question, but since i've never seeing a knock sensor in person, i'd rather ask , what do they look like ? are they bolted outside of the engine ?

[DSteck]

Stock manifolds don't give much room for timing to be added up top. Can't say I'm shocked.

[bluegoat06]

That's another thing, she doesn't have stock manifolds, they're kooks 1 7/8 mid lenght headers with cats. They're not LT's, but they're not as small as the stock manifolds. Oh well, will see, i made a little adjustment to the 9.3-10k HZ using your MAF smoothing tool. I'll give it a try and see what happens although it's cold again tonight so i'm not expecting to see the same KR as last Friday.

Maybe i'll use the exercise as an excuse to get the LT's

[Mez]

Did that already, went from stockers to TR6, ran them for like 20k miles, and now i'm back to the stock heat range with TR5's.

Something i've noticed is that the KR is a lot less when the temp outside is cold like it was today today (50F), with cold IAT's (today at 55-58F IAT) i won't see those 3* KR, it was 1* max, same gas in the tank, in the afternoon with 70*+ (76-80IAT) outside, guaranteed 3* KR by 5200-5600rpm with the timing i currently have in the file i posted.

I can add timing to the IAT modifier and put it back to stock (I zeroed the 86-95F rows), but still, i can't believe this sucker won't take more than 18* at 5200rpm. it's pretty much a stock engine with little exhaust done. dang it.

I would not necessarily worry about the amount of timing it takes if it makes the HP it should. Some people believe the more ignition advance, the more HP. This is true only to a certain point. Some motors I've seen make more power with less advance. Give it what it wants. The LS engines do not require a lot of advance.

For my mods, I ended up at around 20° over 5800 rpm. Before I installed the FAST 92 intake, the stock intake made max power 26°. But I picked up 31 rwhp with the FAST and it needed less advance. Why? The denser the air in the combustion chamber, the less advance needed. How else would it make more power?

Another thing I've been experimenting with is the IAT table. The stock table is pretty good. I read all the time about guys zero'ing out the table below 131° because they don't want the computer pulling timing. Bull hockey. The IAT table is there to match the advance to what the engine needs. Now that the air temp has dropped to ~65° in Texas, I noticed it can take more advance without knocking.

Less advance is needed because the flame front travels faster as the combustion chamber heats up. If you zero out the IAT table below 131° like I've seen done by some tuners, you are not matching the advance to what the engine can use when it cools down. What I have seen work on my engine is set the high-octane table to what makes the most power in the cooler air then let the IAT table take away timing as the air heats up to prevent knock.

[gn2beatu]

Its frustrating for sure, but since its worse when warmer out, its real knock. Mine is the opposite, running 28 degrees above 5200rpm, but I have knock issues in the midrange, like from 3200-4800rpm. Can only run 19 degrees there. In the process of porting my stock manifolds now (hey its free), hope to see a tenth or two and be able to add more timing.

[DSteck]

Ah, for some reason I totally overlooked the mid lengths you listed.

[IDRIVEAG8GT]

Silly question, but since i've never seeing a knock sensor in person, i'd rather ask , what do they look like ? are they bolted outside of the engine ?

Yeah dude, they're bolted on. Sides of the block, directly in the center. They're either a yellow/tan or black. Round units with a single two/three wire plug.

I see stock internal G8's with headers dinking around with 22-24degrees up top. So idk?

[IDRIVEAG8GT]

Less advance is needed because the flame front travels faster as the combustion chamber heats up. If you zero out the IAT table below 131° like I've seen done by some tuners, you are not matching the advance to what the engine can use when it cools down. What I have seen work on my engine is set the high-octane table to what makes the most power in the cooler air then let the IAT table take away timing as the air heats up to prevent knock.

In a nutshell, this is right on.

[bluegoat06]

Gave it a try yesterday, and even at .82 lambda, the engine rattled with only 20* at 5100rpm or so. i backed the timing down to 17-18* and is all good again. So that KR in my logs is not fake, i could hear it too. Damn it.

Makes me wonder if the cats are starting to get plugged ? what other mechanical conditions can induce knock ?

Car runs good otherwise with less timing, i'm behind .1-.2 sec slower than other G8's with LT's and CAI at the same track, but damn it, i can't believe i need to run baby timing when a lot of other G8's seems to do fine with 20-23* in the same area.