Standalone LNF on airboat 6758 turbo help!

Hello I'm hoping someone in here might be able to help me figure this problem out. I've got a LHU running on a LNF 2010 cobalt ecm. Engine is all stock other than a 6758 turbo from zzp. 25 lbs of boost on E50 and 20 degrees of timing. I've been running it almost 2 years now on my airboat. And Recently My turbo broke at the shaft the exhaust wheel was laying in the exhaust housing. So I ordered another 6758 turbo and for a month now I've been fighting with the new turbo. It comes up on boost great. But when I lift the turbo is fluttering. Or shuddering. I've changed the bov valve out and put the one from my old turbo in with no change. I've changed the solenoid. And the plastic Vacuum canister. No changes. So last weekend I hooked the bov straight to the intake manifold . Bypassing the solenoid and canister. It seemed better didn't noticed the shudder as much till later that day I ran the boat through some thick woods putting more of a load on it and the shudder was still just as bad. It's Stalling the compressor so much when I get in and out of the throttle I can feel it loosing power. Not good at all. I'm outta ideas if anyone has any please let me know I've got to get this thing figured out before I hurt this new turbo. Thanks John.

when i ran my 3586R i used 2 tial 50mm bov with a spring that was around 6 or 8 psi iirc. I remember the lighter spring helped open sooner and stay open slightly longer to help get rid of that extra airflow.
A single 50 should be enough. I got rid of the evap solenoid so i drilled and tapped its port so i could screw in a metric to an-4 adapter and ran braided stainless an-4 to both units. One was by the manifold and another on the charge air cooler inlet end tank. If i had to put only one on, i would put it pretty close to the tb.

Thanks for the advise cobalt over booster. Do you think I could still run the factor recirculation valve and put a atmosphere bov before TB and pull vaccum off the manifold for that one? Would I need to retune? I'm not sure what needs to be changed in the tune for running a atmosphere bov?

you can block the recirculation valve off if you install the maf about 8-12" in front of the throttle body and mount the atmospheric bov by the charge air cooler outlet. pull the bov source directly from the manifold with some nice AN hose and you shouldnt have a problem. might need a re-tune for the areas where the valve opens slightly sooner than with a stiffer spring, but it shouldnt change the top end much.
if you leave the maf in front of the atmospheric bov then you will witness erratic fueling behaviors when the valve is open. Maf reads airflow that the ecu thinks will enter the engine. when the valve opens some of that is diverted to atmosphere and now its not fueled correctly as a result of the missing air from the maf sensor feedback.

Before I do a relocate of the maf. Can you think of anything else that would be causing this. What i dont get is i ran the same turbo for over a year and never had a flutter. That turbo broke i ordered the same exact Turbo. And it's been doing this from day one. I did have my maf go out right after I got it going with the new turbo. So I had to recalibrate the maf besides that the tune is the same. I would think the bpv should be able to keep up. The old one did. Going to check for boost leaks this weekend. Thanks again for the feed back.

How did the last turbo die? Catastrophic? You could bypass the charge air cooler and see if it resolves the issue. Catastrophic turbo failure could screw the hell out of the charge air cooler core.

All I can offer is a guess from here. I can?t ride in it and pick up subtle clues from watching it duplicate an issue. I won?t really be much help in diagnosing.

I understand. The old turbo shaft snapped the exhaust turbine was laying an exhaust housing. Looks like the shaft is pinned for some reason it snapped at the pin. The shafts tiny in these things.

So I found a boost leak today. And I did a compression test all 4 holes are dead on 180lbs. I put the bpv spring out of my old K04 seemed lighter. And if I just dead lift of the throttle no flutter. Wide open of half throttle. But if I back out of the throttle like roll off it. Than it flutters could this be something in the tune?

Rolling off the throttle may not be generating enough vacuum

Well my buddy had his 6758 turbo off to replace his exhaust studs. So I borrowed his turbo. His turbo was fine just like my old one. No flutter. I'm stumped. Going to try and pull my old Compressor housing off my broken turbo and put it on the new turbo. Anyone ever seen anything like this before?

make use you don't tap into the boost circuit hoses for a boost reference line from the turbo compressor.
keep them as short as possible.
not sure if this is the case.

Thanks for posting. All the hoses are the factor length. Guess I'm going to try a Atmosphere blow off valve. Can I try this to see if it works before I relocate the maf? Will it just be rich for a second? Just hate to do all the returning if its not going to help.