Annoying misfires mostly at 2000rpm cruise 08 LS3 Vette

[deanm11]

I uninstalled and reinstalled the intake manifold- just to make sure I didn't fould something up when I installed the ported manifold originally. Nothing changed. What was VERY strange was that there was oil accumulated by the intake ports on the heads- now this is normal with stock PCV setup, but I have both the valley and passenger valve cover line going into a dead end breathered catch can (ever since originally doing the manifold and wiping down the original 200 miles of oil). I have how the oil could be getting in the intake runner.

[BBA]

Watch the oil consumption. Chevy has always had a problem with light load moderate cruise RPM oil consumption in the LS6's, they will fix it only on a customer complaint as needed basis, by replacing the pistons loaded with a special (expensive) and oddly shaped ring set.


I had a link to an article describing it but it was also an article in corvette fever a few months back, look for the one where the LS3 was being first talked about.

[drivinfast]

I uninstalled and reinstalled the intake manifold- just to make sure I didn't foul something up when I installed the ported manifold originally. Nothing changed. What was VERY strange was that there was oil accumulated by the intake ports on the heads- now this is normal with stock PCV setup, but I have both the valley and passenger valve cover line going into a dead end breathered catch can (ever since originally doing the manifold and wiping down the original 200 miles of oil). I have how the oil could be getting in the intake runner.

You don't think that the oil can come back thru your catch can lines and be deposited by the intake ports do you?

Or worse yet, it gets there by some other means

[deanm11]

You don't think that the oil can come back thru your catch can lines and be deposited by the intake ports do you?

Or worse yet, it gets there by some other means

No, it can't- the breathered catch can is baffled, it will pull just air.. and further, I dont' think the valley or valve cover are ever under material vacuum. I think the oil comes up past the rings.. wouldn't have thought there would ever be the dynamic for the oil to be pulled toward the intake though...

[BBA]

Actually, blow by will put oil in the intake through the PCV.

[deanm11]

Actually, blow by will put oil in the intake through the PCV.

In my case, none of the PCV is hooked back up through TB or TB elbow... so blow by should be staying in the crankcase.

[deanm11]

I believe I solved the misfire/stumble on this car....

From more and more reports, I was beginning to be fully convinced it was the slot MAF sensitivity... but not fully convinced due to my tests where it still didn't seem to be gone with stock airbox, even still some left in speed density, etc...

Well, it must have been O2 location/switching... as I just swapped out the LG Pro longtube header/magnaflow setup for a full Z06 exhaust from manifolds to mufflers.... and the stumble is gone, with no programming changes. I did hook up the rear O2s with this setup, but haven't undeleted them in the programming yet. I was switching the exhaust setup for somewhat separate reasons- wanting factory appearance, no problems with emissions testing, no annoying minor LG slip fit exhaust leaks.

As a side note, I did speak with a K&N engineer... they are finally getting close to releasing an official LS3 kit. They found that the LS3 cars, when using their Z06 kit (the one I'm using), the tuning was way off on the LS3 cars, unlike the Z06s. In their LS3 kit, they've had to neck down the piping near/leading to the MAF cartridge. No relevance to me or most of us, since I fully retuned MAF and everything else.