I just returned from the dyno, tried the new ECM, same results.
Tried the new 2 bar MAP sensor, same results. Unplugged the knock sensor, same results.

Results:
Engine runs up to any RPM you like and when you hold it there for 20+ seconds, the motor starts seems to lose power and then you can watch the EGTs decrease dramatically. Bring the throttle back to idle and it clears up and is ready for another run.

Is there anything mechanically that could be causing this? I've been advised to do a pressure test on the block to verify that at high RPM, the higher water pressure isn't leaking into the cylinders.

Since I'm now grasping at straws is there anything else that would potentially cause this? Anything you can come up with I will check, this really sucks!

I looked back at your previous post. You have some patience! Are you sure it is in electronics? If you have a carb and intake laying around, why not throw it on and run the motor to isolate the procharger and fuel system? If all runs well with a carb, then you would know it is definetly in the fi system or procharger.

Patience? This is killing me!!!! I have tested, changed or looked at nearly every part of this engine.

What methods are left in troubleshooting the EFI system on the motor? I believe I covered everything. Is there anyway that we are putting a load on the engine incorrectly on the dyno to cause the engine to reat the way I described above and in my other posts?

Are you detonating and the computer is pulling the timing back and then resets the timing when you back off it. Try taking some timing out of it to 28-30 degrees. What is happening to your fuel pressure at 20 secs? Do you lose some?

I also have gone back and re-read your first post although I don't have anything to add that has not been suggested I am going to show the link so maybe someone else will have a idea. I hope you find the answer soon.

Link to other post

My timing is set at 30 degrees. I could lower it just to try it.

As far as detonation, I assumed that if I disconnected the knock sensor the ECM would go into default and wouldn't cause a shut down. But even with the knock sensor disconnected I get the same result.

Scott, thanks for posting the link. I'm sure people are getting tired of my begging for help, but I really would like to be boating this year!!!!

Oh, sorry, fuel pressure is solid at 52 PSI while at boost!

Are you sure you have the correct batt. voltage. You say it runs good at idle and quick revs but start's breaking up under a long load you may not have the right voltage too much or not enough.

seems like alot of fuel pressure ,no its not the dyno,turn off yhe motor when the egt drops a good bit and check the plugs ,is it rich ?? lean?? or water ? ,,I doubt water but maybe
I love fuel injection don't you ?? sorry for your grife !

I'm sure you already checked for valve float? weak springs are a broken inner?,- maybe to much oil in the top end and passing the valve seals? you got us stumped also, what kind of leak down do you have on the engine % ? sometimes on high boost you have to add some more seat pressure to your valve spring's,