Help me diagnose my 2006 z06...

[Thacker]

so looks like we have to wait for the wideband and wot fueling results....

Ed M

I didn't get a wideband or a print out from Vengeance. My dad actually had to take them the car that day because I was working. I was told the AFR was "perfect" at 12.6:1 and that the knock was still happening when the AFR was still good.

I am taking the car back to them Tuesday to try again.

[thesubfloor]

For what it's worth, I've had engine knock in my LS7 at idle with those crappy NKG spark plugs. You might wanna try installing a set of stock ones just to see if it helps.

[schpenxel]

My truck is horrible about something similar. Brand new AC Delco original plugs & wires.. I can run it 100% on the low octane table and it still shows KR.

[thesubfloor]

It looks like you may have a broken valve spring as I've had this happen before too.

If you change the max and min values for your RPM in the scan and turn off everything else, you'll notice how erratic the RPM once you get past 4000RPM. I attached a WOT track pass from my car as a comparison

yours.jpg

mine.jpg

[Nick@Newtech]

i wouldn't surprise me one bit if your car cant take more than 15 degrees of timing, you have stock manifolds and cats, the motor is being choked, cylinder pressure is high due to restrictive exhaust and you have a fast intake and MORE compression than stock you are probably around 11.3:1 and a stock cam that's not lowering your dynamic compression ratio at all. some long tube headers would probably net you at least 25 rwhp and more torque also. If you have the ability to, add fuel reduce timing, if you can hear audible detonation at WOT you are so close to an engine failure, you should be very concerned at this point, and have some kind of tuning done immediately.

[GHuggins]

i wouldn't surprise me one bit if your car cant take more than 15 degrees of timing, you have stock manifolds and cats, the motor is being choked, cylinder pressure is high due to restrictive exhaust and you have a fast intake and MORE compression than stock you are probably around 11.3:1 and a stock cam that's not lowering your dynamic compression ratio at all. some long tube headers would probably net you at least 25 rwhp and more torque also. If you have the ability to, add fuel reduce timing, if you can hear audible detonation at WOT you are so close to an engine failure, you should be very concerned at this point, and have some kind of tuning done immediately.

^^^

[Michael_D]

To follow up with your post at CF, can you describe how you used the top end cleaner to get rid of the carbon from the pistons? (note: the carbon was not cleaned prior to the new head install, and there was an accumulation from oil). I told you in that thread that carbon can, and will be a source of detonation.

You swapped plugs, as suggested, but was that after you ran the cleaner, or before?

I am not sure how a cat can cause detonation. Can someone explain that to me?

The OP can hear it, so it's real. Desencitizing knock sensors is dumb. That is a last thing to do, after you have ruled out everything else.

12.6 is a tad leaner than I like to see. I prefer 12.2 - 12.4 on this engine.

I am somewhat surprised the tuner let the car leave without flashing the stock cal back to the ECM. He may have just forgot.

[Thacker]

It looks like you may have a broken valve spring as I've had this happen before too.

If you change the max and min values for your RPM in the scan and turn off everything else, you'll notice how erratic the RPM once you get past 4000RPM. I attached a WOT track pass from my car as a comparison

yours.jpg

mine.jpg

The erratic RPM on the first pull was due to tire spin, it was blowing the tires off in second gear.

I backed out, got back in it.

[Thacker]

i wouldn't surprise me one bit if your car cant take more than 15 degrees of timing, you have stock manifolds and cats, the motor is being choked, cylinder pressure is high due to restrictive exhaust and you have a fast intake and MORE compression than stock you are probably around 11.3:1 and a stock cam that's not lowering your dynamic compression ratio at all. some long tube headers would probably net you at least 25 rwhp and more torque also. If you have the ability to, add fuel reduce timing, if you can hear audible detonation at WOT you are so close to an engine failure, you should be very concerned at this point, and have some kind of tuning done immediately.

The entire point was I HAD a tune done. This tune was given to me by vengeance. I paid $600 and the car is close to blowing up.... its ridiculous. Vengeance is taking a look at the car again on Tuesday.

[thesubfloor]

The erratic RPM on the first pull was due to tire spin, it was blowing the tires off in second gear.

I backed out, got back in it.

While I don't dispute the wheelspin, it shouldn't be responsible for the erratic RPM. Here's a scan from a while back where I went from cutting a 1.3 60ft to a 1.6 and it spun so bad I hit my 7500RPM rev-limiter yet the RPM stayed smooth all the way.

I also regularly hit 120MPH doing my burnouts but again, my scans never look like that.


wheelspin.jpg

[Nick@Newtech]

The entire point was I HAD a tune done. This tune was given to me by vengeance. I paid $600 and the car is close to blowing up.... its ridiculous. Vengeance is taking a look at the car again on Tuesday.

I agree, if the tune you posted up is what you got, its complete bullshit. I don't see why this car didn't get tuned safely at least. You may had not had stellar dyno numbers, but at least given a dyno sheet with AFR and numbers, no detonation period.

I have tuned this exact setup except .020 thou milling on the heads, timing was no higher than 16-17. part throttle timing also had to be reduced as well, very timing sensitive.

[Nick@Newtech]

here ya go

[realcanuk]

To follow up with your post at CF, can you describe how you used the top end cleaner to get rid of the carbon from the pistons? (note: the carbon was not cleaned prior to the new head install, and there was an accumulation from oil). I told you in that thread that carbon can, and will be a source of detonation.

You swapped plugs, as suggested, but was that after you ran the cleaner, or before?

I am not sure how a cat can cause detonation. Can someone explain that to me?

The OP can hear it, so it's real. Desencitizing knock sensors is dumb. That is a last thing to do, after you have ruled out everything else.

12.6 is a tad leaner than I like to see. I prefer 12.2 - 12.4 on this engine.

I am somewhat surprised the tuner let the car leave without flashing the stock cal back to the ECM. He may have just forgot.

Can be caused if cats are blocked. Unlikely on this car but worth ruling out in case.

[Thacker]

I agree, if the tune you posted up is what you got, its complete bullshit. I don't see why this car didn't get tuned safely at least. You may had not had stellar dyno numbers, but at least given a dyno sheet with AFR and numbers, no detonation period.

I have tuned this exact setup except .020 thou milling on the heads, timing was no higher than 16-17. part throttle timing also had to be reduced as well, very timing sensitive.

My heads have been milled .020... should 16-17 be a realistic timing to shoot for?

[Michael_D]

Can be caused if cats are blocked. Unlikely on this car but worth ruling out in case.

But how? What's the science behind it? If they are that blocked, then the car won't rev to begin with. Seems to me the engine would run rich if they were packed.

Not trying to argue, but understand the 'why'.

[Michael_D]

My heads have been milled .020... should 16-17 be a realistic timing to shoot for?

Yes. I have 18 and that's with really, really shitty 90 octane fuel, no mill. .020" and 93 octane fuel, you should be golden.

Where you might have to pull more spark, is lower rpm areas where you transition into the throttle. I'm actually surprised your KR histogram isn't full of KR, and it's just WOT / open loop. That is a pretty clear indicator you have something causing the detonation, and it's not just from being too lean.

Still waiting to hear how you used the top end cleaner.

[schpenxel]

But how? What's the science behind it? If they are that blocked, then the car won't rev to begin with. Seems to me the engine would run rich if they were packed.

Not trying to argue, but understand the 'why'.

Blocked doesn't mean they have to be 100% totally blocked to the point of the engine not revving

My theory of why blocked cats cause KR--exhaust gases can't all escape because of the back pressure, so you end up with hot gases left in the cylinder after the exhaust valve closes. Combine leftover combustion gases with air/fuel coming in on the intake stroke and you've got a recipe for knock. Higher cylinder pressure and more heat = knock more easily

Sounds like dialing back the timing some more like others have suggested would be the obvious first step though.

[Mep_q8]

If this really was from Vengenace, I'm sure they had a 02 sensor that needs calibration or a new one. As I stated on the other forum, this Z06 is running very lean.

[realcanuk]

But how? What's the science behind it? If they are that blocked, then the car won't rev to begin with. Seems to me the engine would run rich if they were packed.

Not trying to argue, but understand the 'why'.

I can't claim to know the science, but I do know that when mine clogged up I got tons of knock and pinging under any hard acceleration.

[seevi]

OP: check your spark plugs.