low rpm knock with Holley Terminator

[Holliwood]

I have a cammed 5.3, Specs: 212/22X, .498/.498, 107 LSA. BTR springs and pushrods, but other wise stock. 4L60e trans with 3.08 gear.

Under light acceleration and tc locked up im getting some nasty spark knock. I'm running 87 octane pump gas. Can somebody take a glance at my timing table and make sure it doesn't look crazy?

I attached the global file and a data log of the knock.

 

[dyeager535]

I can't open whatever files those are. Can you put them into an Excel spreadsheet or is this some sort of proprietary thing where you need to have Holley software to view it?

 

[Holliwood]

Yeah you have to have holley software. I screenshot these tables. You can see its knocking at at like 1500 rpm and 21 degrees of timing.

 

[dyeager535]

Knock sensor will "see" knock before you can hear it, so IME gives valuable information as to where/when/what to do. Pull a couple degrees in the cells before it starts to happen, and/or add a bit of fuel, see how it takes that. You can hide excessive timing with too much fuel, so I'd caution against both at once. I always pulled timing before the knock event cells and then watched the O2 to make sure the system wasn't adding fuel. Easy fix to bump fueling up a hair until I got it where it should be.

I deal with a manual and GM system, so a bit different with your converter and lockup. No clue if it it would be a proper approach (if this is a computer controlled trans) to make sure converter lockup doesn't happen until load is a bit lower. 20* at 1500RPM's (based on the timing map) means you are really lugging that engine. But I know I can lug mine without knock, so I'd expect just removing some timing in that region would solve your issue. Lovely thing with EFI, it's super easy to try, and if it doesn't work, go back to where you started from.

I don't have my Vortec timing map handy (realizing LS isn't the same) but I looked at a 454 TBI for instance, and timing in roughly the same region you are in, is 13-15*.

 

[Holliwood]

Thank you for the info. This is my first rodeo with efi like this. This morning I pulled 2 degrees out of the area where the knock happened. I also changed the convertor setting to unlock before it loads the engine up that hard at low rpm. Hopefully, that solves that issue.

 

[dyeager535]

Make sure to pull a degree or two out before knock actually happens. You need to pull some where it's actually knocking, but by getting just ahead of it, you'll prevent any weird blips of knock. I'd suggest only pulling what you have to...a little timing goes a long way. Until I started playing with EFI I didn't realize how significant a couple of degress felt.

My opinion in your situation is that even if the converter maybe shouldn't be locked where it's knocking, it shouldn't knock even if it is. You could get into a situation (unlikely) where the converter is unlocked, but RPM's and load are still high enough to be in the same range.

Again, no 4L60E fanatic, but you might want to ensure there are no issues running unlocked too much. I know in the past running unlocked would generate heat, which is obviously no good.

 

[Blue85]

Do you have a WBO2 you can log? That timing looks high to me. I would expect the low RPM, max MAP timing to be more like 12 degrees. The discouraging part is the ECU is pulling like 8 degrees out and the knock is still happening. Is this the knock sensor the engine came with? You could buy premium gas to see how it changes. That's a good way to tell if it's real knock or the sensor picking something else up.

 

[Holliwood]

I do have a wideband, I have been targeting like 15 at cruise and down to 12.5 wot. I have not noticed anything strange with the O2, but I will fill it up with premium and get a log on the way to work in the morning.

I'm running the gm gen3 1 wire knock sensors under the intake.

 

[Blue85]

How did you come to that timing table? I'm not finding other examples of LS tables with so much timing down low. For example, here's a Z06 I found. It would only have 16 degrees in that range where you have more like 27.

 

[Holliwood]

So I based it on a tune I got from the sloppy mechanic's tune cabinet. I changed it trying to add timing during highway cruise hoping to squeeze out a few more mpg, I basically had to shift the curve down in the rpms since I'm running a 308 and a 26-inch tall tire. At 70 I'm only turning 1950 rpm. Here is the table I started with.