Boost dropping to 100kpa during acceleration
 

Hello.
1992 NA 1.6 (I Know) T25 Turbo, external waste gate, MSPNP2, 1200CC injectors, GM Flex Fuel Sensor, DIYAuto Boost controller, Walbro 255LPH fuel pump, 93 octane right now, Tomioka rising rate fuel regulator, BEGI Ex manifold, FM turbo outlet pipe, FM Down pipe, BEGI Coolant reroute, BEGI SS Coolant and Oil lines, BEGI 2.5" down pipe, stock exhaust (I know)

OK that's the particulars of the car, now onto the issue at hand. We have steadily tuned the car to run great during cruise, idle, start up, warm up, etc. I am having an issue that just came up this past weekend.

I will be accelerating from a stop light and if I punch it the boost starts to build like normal then all of a sudden, it drops to 100kpa and makes this sound like it is being bypassed because the waste gate is stuck open, this is my speculation not verified. Car still runs fine, doesn't go rich or lean, those cells are defined and the car runs very normal.

I have put a vacuum tester on the waste gate and it holds a solid 25psi of vacuum and also holds a solid 25psi of positive pressure. It has boosted a solid 10psi for about 4 months now with no drop offs or creep or lag, just a solid performer. I am stumped by this new variable and cannot figure it out. I do have a couple of extra external waste gates laying around and can try one of those this Friday, the waste gate itself seems like it moves freely and doesn't stick. I was wondering if this is a matter of the original waste gate wearing out and me just needing to adjust it???

I hope this post makes sense and isn't just me rambling on :)

Any help would be greatly appreciated

i'd be looking for a boost leak (charge pipes or bov not holding), not at the wastegate. also, wastegate should not see vacuum.

isn't it in vacuum before 100+KPI?

look for the massive boost leak and/or open bov

The wastegate should be sourced pre-throttle. This means that the only amount of vacuum it can see is due to restriction (aka acting like a throttle) in the turbo/filter/piping. But it's realistically going to be 100 kpa when the intake manifold is seeing vacuum.

I have performed a boost leak test up to 25psi and no leaks. When it fails it sure sounds like it is coming from the area of the motor where the turbo sits, i know that is not very scientific but just saying. The car does idle at approx 17-20 inches of vacuum.

I have verified in data logs that the "leak" does cause the MAP sensor to go to 100kpa (atmospheric pressure?) boost gauge also confirms no positive boost. I guess I could take the BOV off and check it out see if it is sticking or not.

The waste gate signal line is connected to the charge pipe of the turbo

Thanks folks got one item to check before I go out and shoot it...lol

For the scientific and logical purpose of deduction, stick to just kpa if you want to make sure numbers line up.

Solved: BOV Opening under boost
 

We removed the additional spring and readjusted using a vacuum gauge per some links we found of all places Google! imagine that, search actually working :P