Losing Boost Pressure...

[Maverick3169]

My boost falls off usually 2-3 psi after exactly 5000rpm in every gear... also seems to spike pretty bad. I have tried everything to fix this, and tested for boost leaks up to 30psi with nothing leaking (except the CBV at 23 psi). Also, sometimes the needle on the boost gauge vibrates when initially going into full boost... this does not happen everytime though.

One thing that I just noticed is that my manifold to turbo gasket is leaking... could this cause these symptoms? I'm really running out of things to try. The only other thing that I haven't tried is replacing my magnacore 8.5mm wires. But I'm not getting any drivability issues at all, and I don't break up.

 

[oldman]

Thanks for that oldman... I think I'll try it out pretty soon.

You're welcome, good luck.

 

[MyBeatGSX]

Sorry to bring this back from the dead, but I figured its better than making a new one.

First off, whats the next best source to tap the mbc to, because I have no intentions of drilling the compressor outlet.

I also had the same problem when I turned by boost down. From a 2,500rpm 3rd gear roll the boost would build very quickly to a steady 18.5psi and then (as with this guy) at exactly 5,000rpm it would begin to fall back to 16psi by the time I hit redline. The wastegate was audibly open the whole time.

So I tried turning the boost back up. In the same situation it hits a steady 20psi very quickly but at exactly 5,000rpm (the magic rev number?) the boost starts a fast creep to around what I think would be 23psi (my gauge only reads to 20).

Of course, going from a past spool rpm roll in either situation results in a huge 3-5psi spike.

Since creep is wastegate related and this guy's boost fall off was wastegate related... I don't see how I can be getting opposite problems caused by the same thing, simply by turning the boost up or down a microscopic amount (like less than 1/8 turn on the mbc).