Knocks on Log
 

Hello guys just want to hear what some of you guys think of the situation. My car is recently picking up spark retard every time I go out to log now. At 1st I thought maybe it was the colder air or bad fuel but I have tried to log again in 65* weather and it still picking up knocks. Now I did notice that it only pick up spark retard when I blip the throttle as if I was about to go WOT. Example would would be that when doing a 60-130 log, it would only record knock on the hit but would not pick up anything after. Even with all this spark retard on the log, it still ran one of its fastest 60-130 time. I am thinking it might be false knock but I have not gotten on it for a few weeks now. What do you guys think I should look for or check 1st? I have tried taking timing out of the area that shows spark retard but it is all over the place and still pick up spark retard after taking out timing. I like to troubleshoot before reaching out to my tuner.

There's A LOT that could be.

It could be in the knock tables by cylinder. It could be burst knock. It could just be mechanical (like supercharger gearset banging around during the transition from off throttle to on throttle). It could be VTT related (TMA).

Have you tried some octane booster to make sure it's not bad gas or something? If not - I'd try to run the tank pretty low. Add enough for a a handful of gallons of fuel. Add a bottle of octane booster (the verified good kind, like Racegas, VP's stuff, or Boostane), or enough such that you're getting, maybe, 100 octane, and see if you still get the retard. If you are still getting retard, I'd really look at those things listed above (and there's more) - might be false knock,or tune related. If it goes away - it's probably too much timing in that area, or something along those lines.

Thanks Radz for the insight. I will be testing the 100 octane soon here to verify it is not fuel related. Then I will probably look at the few things you suggested.

Is the car stock?

Are you doing your 60-130 with traction control on? If so, with 650+ hp, traction control will pull timing to limit tire spin. just a thought.

Car is not stock and it has been tune for the set up. It also pick up some knocks during normal cruise too.

If the engine didn't exhibit this behavior prior and just started doing this, I doubt it's the tune. Tunes don't magically change, but the mechanics of the engine can. So I would start with higher octane fuel and see what happens. Next step would be to look deeper into mechanical issues with the engine.

Thanks! Once I test the with higher octane, if it still shows knocks, I assume that would mean it is probably a engine mechanical issue?

Can a bad exhaust leak cause knock to show up on the log? After a cold start, and once I put the car to drive and give it some gas, around 1k-2k rpm it does have some rattling noise under the car. It goes away after you drive for a bit or the rpm is over 2k. Now the log doesn't pick up knocks during the rattling. However I was just curious if a bad enough exhaust leak or rattling noise can cause knocks under heavy throttle.

Did you add headers? Sometime they can be noisy to the ECM. Could the rattling be there and you don't hear it, when you get under load?

I forget what your mods' were. Didn't you add a 2650?

Radz, you are correct I do have a 2650 on it and headers. The car is basically bolt on with port injection and 2650. I plan to put the car on a lift and go over to see if I can find anything.

Just an update for the group. I did some more reading and found out that the Spark Retard table for Static per cylinder was not Zeroed out. Cylinder 1 still has some value thru out the rpm. I have zeroed that out and now there is no more knocks on my log. Could I assume it was false knock?

Basically - Chevy, essentially, determined that was a cylinder that was prone to knock (?maybe airflow distribution, just noise from the reciprocating assembly/valvetrain/blower gearset [ZL1s]/etc., or something along those lines?) from some factor (and I think there are 2-cylinders for ZL1s that might have STATIC retard...), so it might be, in some circumstances, to say it's false, but they put those there for a reason. I'm not suggesting anything else otherwise, as each car is different, and combinations outside of OEM will differ even more, but it's probably pretty safe to say ZERO'ing that table out is relatively safe on it's own, but I wouldn't mess with KNOCK SENSOR SENSITIVITY without careful "scrutinization" of everything else.

If you're on OEM sensitivity, and on E', without commanding crazy SPARK ADVANCE - you're probably just fine ZERO'ing that whole table out, or - at least start reducing it until you see if go away. That's, obviously, assuming you KNOW you're on good fuel (or at least high octane - 100 even).

It sounds like you're on the right track though.

JMO.

It's common to zero that out but I would be curious to know why you didn't have knock before hand and then it started with the same tune.