L99 with low compression on AFM cyls only

[J-Rod6410]

2011 L99 completely stock internals with Maggie, 9psi, headers, rotofab, and solo catback

While on road course one of the h/f cats collapsed completely and car started running bad.

cruised it home and started checking it for problems and ultimately found the bad cat. It drove normal at cruise only ran bad under load.

Gutted cats, still ran bad........

Checked plugs, wires, injectors and compression etc

Found #6 low only 50 psi

Pulled head and piston was broken/cracked (same side as bad cat)

Replaced piston, rod, rings for cyl 6

Went ahead and eliminated afm lifters, installed all new ls3 lifters and trays, valley cover from Magnuson for LS3, new o rings and gasket from dealer. Cleaned out oil pan, screen etc (skirt had broken off piston also) AFM was already turned off in tune. Also installed new plugs and wires Stock vvt cam was left unchanged.

Car still runs bad. We turned on misfire counters in the tune and found all afm cylinders misfiring intermittently.

Checked compression again, all afm cylinders are at 150ish and all non afm cylinders are 190-200. So obviously this is the problem,

But my question is what could cause this only on those cylinders?

All valves, pistons, etc visually looked good and compression was pretty equal before piston was changed.(maybe all cylinders within 15 psi of each other, don't remember the exact numbers

Any ideas? Im starting to think rings are bad just doesn't make sense that's its on those 4 cyl only.

[sycraft]

cam is probably an issue, vvt function is operated by oil in the front of the cam, I would go with the cam first. , potentially causing a premature valve to open. then check to make sure all valves are sealing and not leaking

[VADER SS L99]

Can the stock AFM cam even be used with LS7 lifters? Also why not change to a small VVT cam with out AFM?

[BplumCrazy-SS]

did you do a leak down test?

[Trob85]

Just delete all that crap, swap out the cam and front cover so you won't run into issues also if you start to swap things out, if you haven't already, turn off the dod setting in the tune. You're computer is probably confused as to why parts aren't in working together and firing as if there're all l99 parts in there.

[Kelly@PCMofNC]

Originally Posted by J-Rod6410

2011 L99 completely stock internals with Maggie, 9psi, headers, rotofab, and solo catback

While on road course one of the h/f cats collapsed completely and car started running bad.

cruised it home and started checking it for problems and ultimately found the bad cat. It drove normal at cruise only ran bad under load.

Gutted cats, still ran bad........

Checked plugs, wires, injectors and compression etc

Found #6 low only 50 psi

Pulled head and piston was broken/cracked (same side as bad cat)

Replaced piston, rod, rings for cyl 6

Went ahead and eliminated afm lifters, installed all new ls3 lifters and trays, valley cover from Magnuson for LS3, new o rings and gasket from dealer. Cleaned out oil pan, screen etc (skirt had broken off piston also) AFM was already turned off in tune. Also installed new plugs and wires Stock vvt cam was left unchanged.

Car still runs bad. We turned on misfire counters in the tune and found all afm cylinders misfiring intermittently.

Checked compression again, all afm cylinders are at 150ish and all non afm cylinders are 190-200. So obviously this is the problem,

But my question is what could cause this only on those cylinders?

All valves, pistons, etc visually looked good and compression was pretty equal before piston was changed.(maybe all cylinders within 15 psi of each other, don't remember the exact numbers

Any ideas? Im starting to think rings are bad just doesn't make sense that's its on those 4 cyl only.

If you delete the DOD lifters you need to change to a non-DOD cam as well.

[J-Rod6410]

Originally Posted by VADER SS L99

Can the stock AFM cam even be used with LS7 lifters? Also why not change to a small VVT cam with out AFM?

Cam was left in due to budget constraints. Lifters were swapped out because heads were already off to check all Pistons so it made sense to swap lifters since a cam was in the future plans. I just don't think anybody has ever done the lifter swap on stock cam.

Originally Posted by BplumCrazy-SS

did you do a leak down test?

gonna try that but its still at 150-160 compression so I doubt that will help. But I will ck compression on the cylinder with new piston and rod which is a afm cylinder. If that one is low, then I know for sure the piston or rings is not the issue since those are new.

Originally Posted by Trob85

Just delete all that crap, swap out the cam and front cover so you won't run into issues also if you start to swap things out, if you haven't already, turn off the dod setting in the tune. You're computer is probably confused as to why parts aren't in working together and firing as if there're all l99 parts in there.

I have an LS3 cam laying around so gonna use that for now. All the DoD/afm settings have been off since the s/c install a year ago. But it does seem that valve timing is off somehow. When I do a compression test on the low cylinders I only get 50-60psi on the first stroke and the higher cylinders give me 100psi on first stroke.

Originally Posted by Kelly@PCMofNC

If you delete the DOD lifters you need to change to a non-DOD cam as well.

Why is that? Are the lobes different between them? That's what I've been wondering.


Sent from J-Rod's Continuum Transfunctioner

[Trob85]

Swap the cam you'll be good to go.

[Who Dat 2SS]

This one is my wife's baby. Thanks for the input!


www.h-towncamaroclub.com

[blisoachle]

You're computer is probably confused as to why parts aren't in working together and firing as if there're all l99 parts in there.

[J-Rod6410]

Originally Posted by Trob85

Swap the cam you'll be good to go.

Yeah got an LS9 cam on the way

Originally Posted by blisoachle

You're computer is probably confused as to why parts aren't in working together and firing as if there're all l99 parts in there.

Yeah that's what it seems but wondering if the lobes are different between the 2 cylinders afm and non afm

Sent from J-Rod's Continuum Transfunctioner

[J-Rod6410]

LS9 cam is in, VVT crap is removed.

All cylinders are equal compression now and Matt is working on the tune.

Sent from J-Rod's Continuum Transfunctioner

[Who Dat 2SS]

All went well in the end. Was misfiring on a few cylinders on the dyno. Still had pieces of the melted cats in the muffler. Swapped the Solo catback for a stock LS3 catback and it cleared up. Made 500/480 on last pull. Needs a MSD BAP adjustment so it may have a few more horses in it.


www.h-towncamaroclub.com

[Trob85]

Sweet glad it worked out and nothing broke internally.