Inconsistent Boost Levels.......

[Slow91Laser]

Alright guys before hitting the track on sunday i decided to have the car retuned on more boost (18lbs) car ran great and pulled hard after the retune for about an hour or so until i parked it.......

Fired her up and started my way to the track decided to do a quick pull and noticed the car didnt pull nearly as hard as the night before, did another quick pull to check the boost gauge and she only made 12lbs........

After adjusting the MBC again to 18lbs the car was fine after getting to the track i attempted to make a pass and found out the boost had fallen back down to 12lbs again.......

This happened about 2-3 more times, after leaving work i did a another quick WOT pull and she made 18lbs i was happy made another pull and she was back to 12lbs again........

Anybody have a clue to why this is happening? Yes i have done a boost leak test and the only leak i have is a very small one from the tb......If anybody has a clue please chime in with your 02.......


Thanks!

 

[MJBean420]

exhaust manifold area? I know I had a pesky exhaust manifold leak that would give me similar results. When the manifold "warmed up" the gasket would leak, not allowing me to hit full boost. Mine was set to like 15lbs and would only make it to like 12lbs and slightly fall after hitting it. Check the exhaust side of things. There might be a leak there not allowing all the airflow to spool/push the turbo to its full potential.

 

[Absit]

Mark your MBC to see if it's backing out.

 

[Slow91Laser]

Bean there is a manifold leak on the wastegate flange that i have blocked off because im still on the 14b but why would it start this all of a sudden?

Absit i dont think it's backing out the locking nut is pretty tight on there and even if it was backing out then it would only make 12lbs all the time instead of 18lbs one run and 12lbs the next run and vise versa.....

 

[RLPerformance]

If its an issue happening on back to back pulls with the engine at the same temp and the air/humidity the same, you can ALMOST rule out exhaust leaks and/or boost leaks. They dont usually come and go that fast. Might not hurt to try another good known MBC and make sure there arent any pinholes in the vacuum line to it.

 

[Tyeler18]

Just run a line from your boost source to wastegate and do some pulls. Boost should stay the same IF its the mbc at fault.

 

[Slow91Laser]

Thanks guys!

This car has a mind of its own its been holding 18-20lbs all day/night .....