limiting hot start knock?

[daktah]

whats the best way to limit knock on hot start? 2013 camaro ls3 m6. right now being a dead stock motor with stock timings and only ever using 91 octane, on hot starts it can sometimes knock once or even 3-5 times quickly in a row. increasing the flare control and retarding start up timing doesnt really do anything either. in the same vein id also like to tame down startup flare (so its a smooth start not an aggressive surge) as much as possible, without compromising its reliability to actually start of course. the adjustments ive made above to combat knock have definitely made it more mild but i want to take it as far as possible for a super stealth startup. no real reason to do this though, i just like it.

[BigTuner]

Can we see a log of this happening and your tune, I feel like that knock isn't a tuning problem, doesn't sound right.

[kingtal0n]

Yeah are you talking about audible knocking or knock in the scanner tool?
Either way an engine shouldn't knock at or near idle, with no load. Sounds like a mechanical problem,
or something way out of adjustment... like way out

[daktah]

Can we see a log of this happening and your tune, I feel like that knock isn't a tuning problem, doesn't sound right.

ok. i dont daily the car so ill have to do it when i have the time.

Yeah are you talking about audible knocking or knock in the scanner tool?
Either way an engine shouldn't knock at or near idle, with no load. Sounds like a mechanical problem,
or something way out of adjustment... like way out

its audible knock, and not at idle but on startup like i said. i dont think its mechanical since it doesnt happen all the time and it goes away immediately after it does or doesnt happen, and it definitely sounds like fuel knock to me. but we will see what the log says when i have a chance.

[daktah]

ok so i went for a 30 minute spin and got the car hot, came back and tried to log the knock. nothing showed up. no hits on knock retard nor on the individual cylinder knock pids, even when it was clearly audible. i started it i think 10 times, it knocked 7 maybe 8 times. i didnt bother saving the log since, well, it shows nothing, but here is my current tune base.hpt. because logging failed i took a video of some startups, it knocked both times in the video but the first one is hard to hear through the exhaust, however the 2nd one is absolutely 100% clear and audible though phone and computer speakers. its like that click/knock nose you make with your tongue to portray knocking on something with your knuckles or whatever.

note that i repeated the footage to prevent it from being a short because screwtube.

[BigTuner]

I'm sorry I can't hear anything, but doesn't seem to be a tuning issue, might have to break out a stethoscope and start hunting or just send it.

[GHuggins]

Spark knock is very obvious when you here it. All I hear is your exhaust changing tones, but my laptops speakers aren't that great.

Just to make sure, you can have someone else fire it up while your standing in the middle of the car and see which way it comes from. Get closer then repeat.

It may even be piston rattle - you can adjust that in the tune, but usually only in play when cold not hot.

[kingtal0n]

I recommend OEM sound level exhaust systems on vehicles to help pinpoint engine related noises.

Try adding 105 or 112 octane fuel and see if the knock stops

stethoscope, quiet exhaust, check valve play, inspect valvetrain hardware, could be piston slap, is the bottom end untouched stock oem? Is the valvetrain stock OEM? Need to consider any aftermarket parts, potential wear, mileage, oil quality, pinpoint noises, octane adjustments per diagnostics etc..

[daktah]

https://photos.app.goo.gl/SYVLRPGSWyGFbS3A6
what about this one? i overrode my npp exhaust to be shut even on startup so its as quiet as the stock system can be. surely it has to audible to you guys now? again, its right as the engine first fires, in this video at about 2 1/2 seconds and right before 10 seconds.

[kingtal0n]

That split second sound of engine pinging?

Here are my thoughts on that.
First I notice the voltage seems to drop a *lot* when you crank. Chhheeeew chhhheeeeewww chhhew chew chew chew start is not good.
-> Indicating either the engine has a very high compression or the battery is weak or weakly attached. Look at grounds, cable attachments, attend these issues. Try attaching a battery charger for cranking to compare the noise with and without voltage added from a charger.

I would focus on this issue as it may ultimately have something to do with the coil dwell when cranking with low voltage causing a high timing advance or early sparking from certain types of coils when the dwell is increased beyond some threshold.

Unlikely but worth ivestigating IMO. since it is essential to have good grounds and a strong battery anyways, and the engine should respond more quickly when you hit the key, even if this isn't the issue it still should be fixed.

Next,

Inspect plugs for oil. A tiny bit of oil in the cylinder will increase compression and cause pinging / death rattle noises similar to what I think I heard briefly.
You may have oil sucking down the intake manifold for some reason. Or through the valve stems or whatever. It may not show up on plugs after the engine is run so maybe check them after it sits overnight or something. Ultimately you may need to perform a compression test, dry and cold, with and without oil in the cylinder to help narrow down the issue.

Next,
Reduce cranking timing a few degrees. Its probably 12 or 13 or something, try 7 to 9 or even less, 4 to 6* it should start easy. This might ultimately fix the issue simply enough.

Next,
Investigate the region of the timing map the engine uses just off cranking. Reduce the timing numbers there.

Next,
As before try a higher octane fuel to see if the issue persist even with high octane.

Next,
Inspect the intake manifold for significant oil residues, investigate the PCV setup. Tell us how PCV is setup- it should be like OEM. You should have a tube running from the intake tube to the crankcase. This is essential to keep oil out of the PCV valve. ALot of people will remove the vent tube from the air filter tract which causes oil to blow into the PCV valve at WOT and ultimately leads to oil aspiration which causes pinging/knock. The fix for this (If you removed the line and/or installed a catch can) Is to remove the unwanted catch-can type devices and restore the OEM air filter tract tubing, you will also need to manually wash out the valve cover baffles and intake manifold as the oil is still trapped inside and won't automatically clear itself.


If you get a powerful cranking, low cranking timing, no oil on plugs, higher octane fuel, clean intake/valve cover baffles, OEM pcv setup, and the noise still persists it may be related to piston rock / piston slap or some issue in the mechanical bottom end

[kingtal0n]

And fwiw I think my engine made that noise a few times when I first started tuning from the OEM configuration. Ultimately it went away as I removed cranking timing and fixed my voltage drop issues. I never heard it again. Which hopefully is a simple fix for you.

[Tunercharged]

I could be wrong of course but I’ve heard this before on a friends 454 with tunnel rams and dual 4150s. It happened after an oil change but he didn’t realize it until me and another friend asked him about the noise a couple of days later. We were like what the hell, then we figured last thing done, the oil filter must not be holding up the oil, that’s why we hear the valve train on startup. Changed filter, problem gone. Good luck!

[daktah]

That split second sound of engine pinging?

Here are my thoughts on that.
First I notice the voltage seems to drop a *lot* when you crank. Chhheeeew chhhheeeeewww chhhew chew chew chew start is not good.
-> Indicating either the engine has a very high compression or the battery is weak or weakly attached. Look at grounds, cable attachments, attend these issues. Try attaching a battery charger for cranking to compare the noise with and without voltage added from a charger.

I would focus on this issue as it may ultimately have something to do with the coil dwell when cranking with low voltage causing a high timing advance or early sparking from certain types of coils when the dwell is increased beyond some threshold.

Unlikely but worth ivestigating IMO. since it is essential to have good grounds and a strong battery anyways, and the engine should respond more quickly when you hit the key, even if this isn't the issue it still should be fixed.

battery is fairly new and good, battery cables and connections have 0 resistance as far as my multimeter is concerned. fwiw both of my dads camaros (2010 2ss then 2012 zl1, both bought new off the lot) always had a similar slow crank. dont remember if they knocked tho, never really listened or noticed.

Next,

Inspect plugs for oil. A tiny bit of oil in the cylinder will increase compression and cause pinging / death rattle noises similar to what I think I heard briefly.
You may have oil sucking down the intake manifold for some reason. Or through the valve stems or whatever. It may not show up on plugs after the engine is run so maybe check them after it sits overnight or something. Ultimately you may need to perform a compression test, dry and cold, with and without oil in the cylinder to help narrow down the issue.

no oil on plugs, no significant oil consumption (<1/2 quart over 5k miles, and i hammer this thing daily), no smoke, no smell. ill compression test if all else fails but seems unnecessary since cranking, idle and power output is smooth and even. obviously not like i6 smooth and even, but you know as smooth and even as a crossplane v8 should be.

Next,
Reduce cranking timing a few degrees. Its probably 12 or 13 or something, try 7 to 9 or even less, 4 to 6* it should start easy. This might ultimately fix the issue simply enough.

these are my startup tables. beforehand i retarded the timing and increased the flare control to try to make the startup smooth and controlled instead of the normal huge flare. yes it did knock before i even bought hptuners.
Untitled.png

Next,
Investigate the region of the timing map the engine uses just off cranking. Reduce the timing numbers there.

ill look into that this weekend hopefully

Next,
As before try a higher octane fuel to see if the issue persist even with high octane.

91 is the highest in my area short of $9 a gallon 100 octane ive seen at exactly one station, id rather fix it with a tune than lock myself into $150 fillups and one single station

Next,
Inspect the intake manifold for significant oil residues, investigate the PCV setup. Tell us how PCV is setup- it should be like OEM. You should have a tube running from the intake tube to the crankcase. This is essential to keep oil out of the PCV valve. ALot of people will remove the vent tube from the air filter tract which causes oil to blow into the PCV valve at WOT and ultimately leads to oil aspiration which causes pinging/knock. The fix for this (If you removed the line and/or installed a catch can) Is to remove the unwanted catch-can type devices and restore the OEM air filter tract tubing, you will also need to manually wash out the valve cover baffles and intake manifold as the oil is still trapped inside and won't automatically clear itself.

oem pcv setup is just a plastic can thing that screws into the oil neck with a little floating valve thing inside it hooked to the intake pre throttle. i took off the line and there is 0 standing oil in it nor dripped out of the intake tube (connection is on the bottom) so idk if that is a good or bad sign (since again i hammer on this thing every time i drive). when datalogging the computer does log knock at wot and higher rpms but i cant hear or feel it when doing it so idk if its real or false knock in the first place, especially since ive only ever use 91 and have never touched the main spark table.

If you get a powerful cranking, low cranking timing, no oil on plugs, higher octane fuel, clean intake/valve cover baffles, OEM pcv setup, and the noise still persists it may be related to piston rock / piston slap or some issue in the mechanical bottom end

i dont really think its mechanical, especially since it happens only immediately on startup, only when hot, and there are no other hints of mechanical problems (like oil pressure or low/inconsistent power). if the opposite were true i probably would have the motor apart already.

And fwiw I think my engine made that noise a few times when I first started tuning from the OEM configuration. Ultimately it went away as I removed cranking timing and fixed my voltage drop issues. I never heard it again. Which hopefully is a simple fix for you.

im thinking and hoping its just the immediately off cranking timing being a bit high for the motor for whatever reason

I could be wrong of course but I’ve heard this before on a friends 454 with tunnel rams and dual 4150s. It happened after an oil change but he didn’t realize it until me and another friend asked him about the noise a couple of days later. We were like what the hell, then we figured last thing done, the oil filter must not be holding up the oil, that’s why we hear the valve train on startup. Changed filter, problem gone. Good luck!

ive always had good pressure and have changed the oil at least twice with pennzoil platinum and wix filter with this problem, plus it absolutely sounds like knock not valvetrain/mechanical (i own a ford 4.6 and 5.4 so i know allllll about valvetrain noise). i dont think its that.

[smokeshow]

These tend to be preignition that results in detonation, not your spark plug causing it as it starts delivering spark. Not much you can do about fuel you didn't want in there igniting with a heat source you didn't supply.

[peter logan]

sounds like lifter noise to me ? lifters a bit weak until oil pressure builds up.