DYNO-Top end power loss and shake! SUGGESTIONS??

Alight guys, I keep running into problems with the GVr4! I get little things fix and move on but something else always seems to pop up at the worse time.
Just went to get my E85 dyno tuned over the weekend. I have the boost set at 17psi, e85 fuel pressure is up at 40psi as my initial tune to make the GVR4 run much smoother. Initially, First issue was solved by replacing the old ass iridium spark plugs. With the COP installed, we could tell it was time for the plug change. After the plug change, my first run gave out 266tq and 260's whp. I was hoping to make little more HP at the top end but car was not behaving. Pretty decent run with lot more room to work with! I was thinking at this moment, when we get the top-end figured out, I was going to raise the boost up to about 20psi. I never reached that goal! The initial tq/whp and boost is there and Power rises smoothe. And even at top end, boost does not drop it actually rises! my problem is at the top end? And we noticed it that the problem varies on every run. To put it simple power drops at the top end! We are monitoring the boost and fuel but power drops at the top-end as car shakes a little to show that its fighting/sturggling! Everytime power start to drop where it's not suppose to, we just back it down not to hurt the motor. When we review the dyno sheets, the power loss comes in at different rpm. I also noticed when gas is let go at the high rpm, little bit of smoke comes out by the from of the engine/turbo area. I asked the tuner about the smoke coming out of the front and he was thinking that it was blow by/past from turno when he let go the boost. But maybe there is a problem there too?
Well, that's pretty much it!
GVR4 still drives nice out on the road. I put little bit of oil just in case. I don't boost at the top end but everything is normal and I can get around pretty quick with mild boost. I would like to figure out and find out what this GVR4 can do? But I'm thinking maybe the car is feeling its age! Could the shake and power loss come from the shaft? This is definately high top end issue only? I really don't get how these GVR4 works sometime?

 

[onesickcrx]

Why don't you start off with the basics do a compression test and or a leak down test. By doing these tests you can verify motor is good or bad and where the issue is if there is one, If thats good you can start looking else where. The smoke you see is it a exhaust leak? That could do everything your having issues with...

 

My tuner thought it was maybe the compression for a second. That's a definite possibility but he was also thinking that maybe valve is sticking. It just that sudden drop in power occurs at different RPM, he said it will be hard to pinpoint the exact problem. I am sure shaking and losing power is where the problem is coming from. Good boost and good hold on boost, but power drops at the top end when the car starts to shake. I will do couple of things to diagnose the issue. I am looking for additional hints/areas that I should check during this process. Just checking if anyone with GVR4 had similar problems or incident with their ride.

 

I had the chance to look over the motor recently and found that injectors were just sitting/fitted with fuel rail bolts requiring about 1/4 inch tightening. (Being fitting into the combustion chamber, I'm thinking that compression leak could have been coming from the injector holes during the high rpm) I'm hoping this maybe the cause for the power loss at the top end. The injectors are totally different compare to Rc's that I previously had in there. I will test it out but little bit afraid that I might do more damage to the motor.

 

[gramkrakr89]

(somebody please chime in if i'm way off base here, heh)

Boost leaking at the injector seat is a big problem, because of the uneven combustion between cylinders that can be occurring due to different A/F ratios for each cylinder (this can also exhibit the appearance of bad compression, due to uneven firing...?)

If you found definite boost leaks at the injector seats, and fixed them, then you've eliminated one very likely cause of top-end power loss (at higher boost, your injector seats could have been lifted just enough to allow a decent amount of air+fuel to escape, causing uneven combustion...?)

As long as your compression/leak-down tests turn out well, I wouldn't hesitate to test and re-tune your setup after finding/eliminating all of your intake leaks... It may likely have been leaking all along, causing all of your tuning thus far to be way off, so a re-tune should be done anyway.

As for your smoke, what kind of turbo are you using?

 

[Eaglesfly]

I would always suggest a boost leak test prior to looking anywhere else for any type of running issue. I'm also thinking that the MAS may also be going bad. It is possible that it's dropping airflow counts in the higher RPM/boost range. Since I'm not sure what your using to tune with, it's hard to diagnose that, other than swapping the MAS. If using DSMLink, you can look at the MAFRaw and see if there is consistancy with the Htz reading when the shuddering starts to happen.