What could cause a turbo to suddenly create too much boost when nothing was changed? The waste gate actuator arm was removed and the arm wired to full open. So, this 2nd gen turbo, which looked bone stock, would boost up to 12lbs with the waste gate fully open.....wtf? We tried everything we could think of to get this guys boost to normal range. He made a few runs, all was fine. He goes on a night ride (was in a sand rail like mine) and suddenly his motor is boosting no matter what we tried.....anyone have that experience?

 

Answering in somewhat of a vacuum of information, but your mention of "night ride" suggests a lot cooler ambient temperatures. Cool air = denser air. Denser air + opened/less restricted intake w/o boost control = boost spike.

 

what was it boosting before the issue? it could simply be boost creep. the S4 turbo has a rather small wastegate which is very prone to creep, the S5 is a bit larger but still can creep on moderately to highly modified setups.

 

the s4 turbo only bleeds exhaust from one runner, and thus can result in uncontrollable boost creep.

the solution is an aftermarket external waste gate( and manifold).. or a different turbo.

 

Well you guys give good examples to consider, however they don't really apply to this scenario. We forced the waistgate to remain open the entire time and it boosted anyways. How does it create boost when the exhaust gate is open the entire time? 4lbs was what it was supposedly making before it started this weird phenomenon....

 

you aren't getting the big picture.

just because the wastegate is forced open doesn't mean ALL the exhaust is bypassing the turbo. look at how small the holes are that allow exhaust to bypass through the wastegate and think about it, they aren't really that big..

4psi is abnormally low, i assume somehow you repaired a boost leak without even realizing it. even the lower boosting S4 with lots of restrictions opens the wastegate at 7.4psi(if memory serves, i don't see many stock cars anymore). that is the bare bottom lowest boost one should normally see.

 

Well, some how repairing a leak is a possibility, however unlikely. I get it, trust me, which is why it has thrown us for a real loop. As I indicated, IT HAS NEVER made boost like that. It is a tired 13b turbo in a Beam front end rail, its old. I think it's about to blow up and some part broke loose, is plugging something else up, maybe the exhaust, OR maybe his spring in the waist gate is no longer rusted open and is working properly. In fact, I think that is exactly whats going on now that I think about it ..... I am willing to bet his blow off valve has been stuck open, ie his **** poor boost, and is now closed allowing his boost to build again....... Holly crap batman, I gotta call this fool..........thanks guys