Really fubar'd timing issue during WOT on a cammed LS2

[DSteck]

See the attached log. This was happening on the dyno, and is super obvious when it's happening. You don't feel it on the street so much unless you're in 4th.

Anyway, when going WOT below 2000rpm, you can feel the car start to shake, get worse, then get better and totally clear up by 3000rpm. You can see the knock retard spikes make a bump that peaks around 2500rpm... If you punch it from 2500rpm, the spikes peak out immediately and decay down. I backed out a TON of timing, and it was still doing it.

I have a hard time believing this is actual knock, and it wasn't torque management. I have absolutely no idea what is doing this.

The cam is a 231/239 0.624/0.624 on a 113 LSA, and the car has Dynatech headers and a Callaway Honker intake.

Any ideas on what the hell is causing the KR spikes? I have never seen this before.

[Russ K]

That's burst knock, not spark knock. Zero out the burst knock table.

Russ Kemp

[DSteck]

That's burst knock, not spark knock. Zero out the burst knock table.

Russ Kemp

Why would burst knock be interferring in this scenario? I'm not saying you are wrong, but I've never seen it before on any of the cars I've ever done.

I'm not surprised to see it when the throttle is stabbed, but seeing it come in and out is really weird. The fact that the MAF has so much fluctuation while it's happening was making me lean towards burst knock, but I couldn't justify it out of stubborness.

[Blackdevil77]

I don't think its burst KR. You can log burst kr seperately from KR. Your logging KR, not total KR, so it's not burst. Do another pull and log both KR, and burst KR

[thesubfloor]

Why would burst knock be interferring in this scenario? I'm not saying you are wrong, but I've never seen it before on any of the cars I've ever done.

I'm not surprised to see it when the throttle is stabbed, but seeing it come in and out is really weird. The fact that the MAF has so much fluctuation while it's happening was making me lean towards burst knock, but I couldn't justify it out of stubborness.

I'm pretty sure you've got something hitting the block or frame as the knock patterns are too similar and repetitive to be anything else. When I installed the LS7 in my car I had an issue with the passenger side header hitting the floor and it caused a very similar problem.

I also think the reason the MAF is oscillating like that is because it's simply following the pitch of the engine as the timing rises and falls.

[DSteck]

I'm pretty sure you've got something hitting the block or frame as the knock patterns are too similar and repetitive to be anything else. When I installed the LS7 in my car I had an issue with the passenger side header hitting the floor and it caused a very similar problem.

I also think the reason the MAF is oscillating like that is because it's simply following the pitch of the engine as the timing rises and falls.

That's very possible. I didn't do any of the labor on this car, and it DEFINITELY has extremely audible valvetrain noise that is at it's worst around 2500rpm. However, why would a mechanical impact cause burst knock to trigger instead of actual knock retard?

I cut burst knock down to 33% of it's original values. It still shows up in the scan, but you can't feel it anymore... Instead of eliminating burst knock completely, I wanted to try leaving a little in... and it worked, so I'm going to call that one done. Thumbs up to Russ K. It figures... the first car that I leave burst KR alone in ends up having a really intrusive issue with it. Haha.

[Snyper]

Whats the difference between burst knock and regular knock?

[carlrx7]

regular knock is real, ouch it hurts knock, burst knock, is the computer flinching before it gets punched in the arm

[DSteck]

regular knock is real, ouch it hurts knock, burst knock, is the computer flinching before it gets punched in the arm

Hahaha, I like that. Nice.

[5_Liter_Eater]

Like Carl said. Burst knock is the PCM anticipating knock and preemptively taking timing out. Mine is zero'ed out. But if what blackdevil said is true then this is not at all burst knock. Would need more granular KR scanning to be sure. Wouldn't hurt to log the individual cylinder KR too so see if it's a particular cylinder.

[99LS1SS]

regular knock is real, ouch it hurts knock, burst knock, is the computer flinching before it gets punched in the arm

Thank you for the description. That's a good analogy!

[carlrx7]

i recently zero'd my burst knock, and all my lower g/sec knock dissapeard

[DSteck]

Like Carl said. Burst knock is the PCM anticipating knock and preemptively taking timing out. Mine is zero'ed out. But if what blackdevil said is true then this is not at all burst knock. Would need more granular KR scanning to be sure. Wouldn't hurt to log the individual cylinder KR too so see if it's a particular cylinder.

It was burst knock. I used to log burst knock along with total knock retard, and would filter stuff out, but stopped doing it because I never found any value added. Go figure.