NA Solstice gone turbo, chasing odd misfire counts on cyl4 but no obvious reason??

See if anyone has any ideas. Shows misfires at WOT on cyl4 at upper RPMs pretty consistantly.

Compression test was around 150# across board, less than 5% leakdown across all (forged pistons/rods)
80# new injectors, new NGK 7 plugs
doesnt follow coils around
Comp cam, has new springs, balance shaft delete, 10.5:1 compression
cam, crank and knock sensors been replaced

KNock sensor goes off a ton at 9 degrees of timing he sent me from tune thats in it, going to clean that up first but it doesnt do it there does it up top when knock sensor isnt showing and its at 10 degrees of timing. Doesnt seem like much but? pump gas right now, 7 or 8psi

Check out your spark plug gap first, try setting it to 0.6 mm.

If that does not solve the issue, try swapping the order of the injectors, misfire might move to another cylinder if it's a bad injector.

I don't know about slamming the gaps to .023" right off the batt. If the pressure is lower like 10-15 psi then .032-.035" is probably enough. High rpm breakup would be across the board and that would tell you to be tighter, but my guess not much tighter than .029".

I vaguely remember the Soltice coming with Dual Mass Flywheels (DMF) that set cylinder 4 off on occassion. A long time ago, one of my friends found his DMF causing issues by running VP110 through the engine with no change. All the plugs were the same.
Hows the ground strap on #4? If its the only one thats hot then it could be an injector issue. Maybe some debris in the injector inlet? Does this one have injector cups in the head? Sometimes they crack from heat cylce fatigue during the injector swap and air leaks through under boost making a slightly rich cylinder. It would be leaner than the rest under idle when vacuum is present.
Plastic manifold - look for separation cracks along the runners under pressure. Not so easy to check, but also not boost proof unfortunately.

I'm really bad about logging on these days. I might not be providing the best help, but those were the easier culprits to look at.

hows the coils connection to spark plug ? if thats a bit worn or not properly clipping in it can be ok at lower rpms but miss when its under more demand up top, is it actually missing as u can see it in the 02 sensor ? or is it just the code showing up but engine runs fine

Quote:

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Originally Posted by cobaltssoverbooster

I don't know about slamming the gaps to .023" right off the batt. If the pressure is lower like 10-15 psi then .032-.035" is probably enough. High rpm breakup would be across the board and that would tell you to be tighter, but my guess not much tighter than .029".

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I had spark blowout at 15 psi on an engine with 9.5:1 compression ratio. 10.5:1 will only make it worse. It will work fine at that close of a gap and you can eliminate that possibility at least if it works or does not work.
Of course i do recommend putting them back to a higher gap when you resolve the issue.

It's also worth mentioning not all plugs are gapped properly from the factory.


Edit:

On the topic of spark plug gaps - it's more of an air density issue than a boost pressure issue. Ironically i had a 1.0 mm (0.039'') gap NOT blow out at 1.3 bar (19 psi) of boost because the air was that hot.
The engine from the factory was designed to run 0.70 mm (0.027'').

And then you slap on a bigger intercooler and suddenly it does not work.

set your gap to .019 and you will be golden.. i just tuned 1 of those, really close s etup. it started to blow spark at 10 psi with gap at .035
make sure you have the correct spark plugs, the ones with the long thread.

For the guys that said injectors, they are new injectors just changed so - not it
Gaps are .026 he said, NGK rheuthenium or whatever they are called, I have no experience with these I use Iridium NGK/Denso only. That said .003 in gap isnt likely going to change that, and it wouldnt show up on just one cylinder

He said he had already moved coils around, so that should present itself on another cylinder if connection issue

What kind of timing are you running and what power level/fuel?? Its been 7 or 8 years since Ive done any Ecotec 4cyl stuff honestly

Even though I knew it wasnt it, tightened gap down all the way to .017 and no better

Can clearly see misfire counter go ape shit on dyno pulls. Airfuel 12.3 to 10.8 doesnt matter

dosnt look like ur actually misfiring as u would see it in the 02 sensor it will pick up little blips but it stays steady, ur getting alot of little knock tho so maby its alot of noise its picking up on may have to see if thats actual or not and if its not adjust the knock sensitivity, if u have a camshaft u also have to setup the misfire settings or disable them as u will get false readings if its too far from stock

Quote:

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Originally Posted by 07GTS

dosnt look like ur actually misfiring as u would see it in the 02 sensor it will pick up little blips but it stays steady, ur getting alot of little knock tho so maby its alot of noise its picking up on may have to see if thats actual or not and if its not adjust the knock sensitivity, if u have a camshaft u also have to setup the misfire settings or disable them as u will get false readings if its too far from stock

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Misfires from the camshaft would show up at low rpm, light loads where the reversion is actually occuring more than stock, not starting at 5500rpm at wide open throttle. It does have cams in it, but they are barely bigger than stock and dont show any misfires idling. Also it wouldnt be just on one cylinder primarily, it would be even-ish across them all

Quote:

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Originally Posted by sbarisic

I had spark blowout at 15 psi on an engine with 9.5:1 compression ratio. 10.5:1 will only make it worse. It will work fine at that close of a gap and you can eliminate that possibility at least if it works or does not work.
Of course i do recommend putting them back to a higher gap when you resolve the issue.

It's also worth mentioning not all plugs are gapped properly from the factory.


Edit:

On the topic of spark plug gaps - it's more of an air density issue than a boost pressure issue. Ironically i had a 1.0 mm (0.039'') gap NOT blow out at 1.3 bar (19 psi) of boost because the air was that hot.
The engine from the factory was designed to run 0.70 mm (0.027'').

And then you slap on a bigger intercooler and suddenly it does not work.

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Of course thats how it works. The cylinder has no idea what your boost gauge reads. It only knows the air density and therefore the cylinder pressure its trying to arc through

Gap at .016 even did nothing to fix shown misfires

Is the turbo surging at that amount of boost?

Attachment 125090

The MAF signal looks a little bit more wavy than it should. What's the MAF housing diameter?
What happens if you decrease the boost by 10 kPa?

You could try advancing or retarding the intake cam by 1 degree and see if that has any effect on the misfiring.

Its a 3" very straight section of pipe. Cant decrease boost by anything, its on the wastegate spring right now as low as it will go.

If your looking at the log boost appears to be very steady, not surging at all

Quote:

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Originally Posted by GrannySShifting

Comp cam, has new springs, balance shaft delete, 10.5:1 compression

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