Misfiring and aggressive knock only at WOT above 5K rpm on LS7

[shoaf85]

LS7 forged pistons, AI heads and custom PatG cam. BR7ef plugs with out of the box gap


Alright guys I've got a C6Z on my dyno here and we are getting some pretty aggressive knock. I noticed it on the first pull and let out. Since then I have made a couple more pulls while changing plugs, coils and wires with now affect at all. I've pulled timing as well with no change. When the car got here for tuning it did have a light popping/mis under light driving conditions, I changed the plugs and that went away. Gonna change the plugs again just to eliminate that when the car cools down.

The car will rev perfectly fine all the way through the rev range until you put a load on it. I can drive the car all the way to 6500+ rpm at part throttle on the dyno but as soon as I go wot the car will start to miss and I see a LOT of KR. Now I have had this car on the dyno before and this issue wasn't here. Different cam and pistons in now are the only changes made (for nitrous). Clearly something has changed physically to cause this issue so I am just mainly looking to see if anyone has seem similar issues with misfiring and KR. I have had spark blowout before and this is kinda what it seems like is happening but I never see KR like I'm seeing when that occurs. Possibly a crank sensor is going out or knock sensor? Any advice or help is greatly appreciated.

I have attached the current tune file and two logs. One log is a 4th gear pull and the second log is two 3rd gear pulls, first pull is at part throttle all the way to 6+ and pull right after in the same log is wot to show knock. There are no misfires showing up on the log but it is missing and popping loudly but only where the KR occurs.

d2.hpl
pt run.hpl
maf 5.hpt

[ColeGTO]

How about injector(s) or fuel pressure? Part throttle is going to have a lot less fuel demand even at 6K+. Maybe it's lean. How are the AF's at PT and WOT?

[shoaf85]

UPDATE NEW PLUGS DID NOT HELP

As far as fueling goes yes the fuel is good. Pressure is holding steady at 60psi throughout and lambda is .85-.87 throughout the pull. AFR reading is in the logs. The car has ID injectors in it.

[jsllc]

Considering you have symptoms to match sensors "missing and popping loudly but only where the KR occurs" then I would believe the sensors. "Different cam and pistons" are the best clue. I do think you have some fueling issues based on the logs.

Just now getting a motor rebuilt that has similar issues. Had mis-fires down low and up high. KR changed after build by company. Figured it was just he way it was, new norm. Found out bad build. The KR was piston slap due to excessive wall clearance on pistons and not enough gap on rings. Lost some compression, leak down test showed large variances. New build coming. Hope it is not something like this.

[shoaf85]

Considering you have symptoms to match sensors "missing and popping loudly but only where the KR occurs" then I would believe the sensors. "Different cam and pistons" are the best clue. I do think you have some fueling issues based on the logs.

Just now getting a motor rebuilt that has similar issues. Had mis-fires down low and up high. KR changed after build by company. Figured it was just he way it was, new norm. Found out bad build. The KR was piston slap due to excessive wall clearance on pistons and not enough gap on rings. Lost some compression, leak down test showed large variances. New build coming. Hope it is not something like this.

What type of fueling issues are you seeing?

The tune isn't finished up yet but the afr is not far off!

[shoaf85]

Found the issue. Ground wire was not connected on the side of the block. Bolt just above the driver side knock sensor!

[jsllc]

So in the log d2.hpl this is the error. the big change at the end is of interest. 0.85 to 0.82 or lower are safe lambda values. Also on a 108MM air intake on a 418ci stroked LSA I have much different slope for MAF and less air. Do not know all mods, just pointing out variances.
2018-01-11_14-56-01.jpg

[jsllc]

Found the issue. Ground wire was not connected on the side of the block. Bolt just above the driver side knock sensor!

Good find. Grounding is always vital on these.

[jsbaugh]

Dont keep low octane timing the same as high. Good way to blow the motor up.

[shoaf85]

I always keep them the same when tuning ve and maf separately but will change back when I’m finished and convert the tune beck to a blended file. We have many setups that don’t even use knock sensors so with proper ignition tuning it won’t “blow the motor up”

[Higgs Boson]

Dont keep low octane timing the same as high. Good way to blow the motor up.

nonsense

[jsbaugh]

I always keep them the same when tuning ve and maf separately but will change back when I?m finished and convert the tune beck to a blended file. We have many setups that don?t even use knock sensors so with proper ignition tuning it won?t ?blow the motor up?

Interesting considering if you werent using knock sensors when tuning this car you would have blown it up.

[shoaf85]

It wasn’t real knock. As soon as i found the ground wire and fixed it the same calibration had ZERO knock. I knew it wasn’t seeing knock by reading the plugs......

[Higgs Boson]

Interesting considering if you werent using knock sensors when tuning this car you would have blown it up.

how did we do it for all those decades before knock sensors? knock sensors are not for tuning. if you are "tuning" spark with knock sensors you are doing it wrong.

[jsllc]

how did we do it for all those decades before knock sensors? knock sensors are not for tuning. if you are "tuning" spark with knock sensors you are doing it wrong.

If you believe there is a better way show people. Most would gladly learn. This is not helpful to anyone.

[Higgs Boson]

If you believe there is a better way show people. Most would gladly learn. This is not helpful to anyone.

That's the real issue, that people only know how to rely on a knock sensor which is the actual real way to risk either blowing up a motor or the opposite, leaving power on the table.

You've never heard of a spark hook test or simply using a dyno to find MBT? Are you tuning other people's cars? Hope not.

This forum is about using HPTuners to tune, I never realized it was to teach people tuning basics. And that isn't even the problem in this thread, the issue is jsbaugh giving someone else some lip when he isn't even correct and that's all I am addressing here, not attempting to lead a spark tuning school.

We made tons of power for many years before fuel injection, knock sensors, computers, and so on. Actually, we still do!

[Higgs Boson]

a quick and simple search, maybe it will "help" you

https://www.hptuners.com/forum/showt...l=1#post298723

[Ben C]

That's the real issue, that people only know how to rely on a knock sensor which is the actual real way to risk either blowing up a motor or the opposite, leaving power on the table.

You've never heard of a spark hook test or simply using a dyno to find MBT? Are you tuning other people's cars? Hope not.

This forum is about using HPTuners to tune, I never realized it was to teach people tuning basics. And that isn't even the problem in this thread, the issue is jsbaugh giving someone else some lip when he isn't even correct and that's all I am addressing here, not attempting to lead a spark tuning school.

We made tons of power for many years before fuel injection, knock sensors, computers, and so on. Actually, we still do!

Well said.

[jsllc]

Do not know how attempting to insult me helps either. I surely was not looking for your help. Slamming people all the time must get tiring. Do not see the need. A simple this is a better way would have helped those looking for it. Your rude condescending tone that you take with those you deem to beneath you has no place here. This forum has no requirement for you to approve what others think. Help or not your choice but you have no right to demean others.

[Jon S.]

Do not know how attempting to insult me helps either. I surely was not looking for your help. Slamming people all the time must get tiring. Do not see the need. A simple this is a better way would have helped those looking for it. Your rude condescending tone that you take with those you deem to beneath you has no place here. This forum has no requirement for you to approve what others think. Help or not your choice but you have no right to demean others.

You thank you for always trying to help others. Thank you again for pointing out poor manners, which is really a lack of basic respect for other people.

However, in our “modern world” social media seems to have given the ill mannered and boorish a forum to act like children. No one in the corporate world would act this way in their workplace, as it would limit their career aspirations.

The anonymity of social media seems to bring out the worst in some people’s manners (or lack thereof). It is doubtful that such interactions would ever occur in face to face communications - not if you ever expected the other person to speak with you again.

This particular instance is relativity minor, in comparison to some that I have read over the years. There are some posts on this forum that would have cost the person their consciousness 40 years ago - when manners seemed to be more commonplace and valued. The world gets better, and worse, all at the same time.