losing boost topend, too much low end...

[Justin99GST]

i looked around in past forums and problem diagnosis for about an hour but couldnt seem to find what i was looking for. at wot my car hits 14psi then around 5000 to 5500 rpm, it goes rich on my a/f gauge and i being to slowly lose boost. but today i was in fifth gear at about 45mph and floored it to get back up to speed when some slow car got out of my way(i didnt down shift just left it in fifth). it spooled up to 14psi then suddenly jumped real quick to 19psi on the analog and 1.21 hkPa on the blitz and there was a really weird "popping" sound, i got to a place where i could pull over and looked under the hood, nothing visually wrong, exhaust was not smoking, and the idle was just fine. what would cause something like this? if i need to do a boost leak test that shouldnt be a problem i have a friend with a couple of turbo supra and a r34 skyline gtr so im sure somewhere in his garage he's got the stuff to do it.

 

[brute]

Maybe you have an exhaust leak somewhere that is causing boost problems. The exhaust leak may also lead to misfiring (popping sound). Correct me if I'm wrong.

 

[Justin99GST]

If I do have an exhaust leak it's a small one cause I hear anything. Also i wanted to clarify something too, when i said losing boost pressure I go from 14psi down to about 11-12 psi before I have to shift.

 

[mavisky]

Double check all your vacuum lines. It sounds like one of them may have come loose or completely off.

 

[oldman]

Spike=>settle=>drop off after 5k rpm = T25, sounds pretty normal to me especially if you still have the stock 2G BOV. Upgrade to a 1G BOV (recirculate), perform a boost leak test, changing back to the compressor housing if you're tapping the bov line for your mbc and installing an afpr for your 255 will greatly improve your situation.

 

[Justin99GST]

I have a recirculated hks bov, I am hoping to get a afpr with my next check. Unfortunately i kinda figured the drop off was due to the stock t25, that will change soon. I actually have an electronic boost controller from blitz, i have tried every possible way to hook that damn thing up and i still cant get it to work right. I have tried compressor to solenoid to acutator, I've tried putting a t-fitting to the bov from the compressor to solenoid line and the only thing that really changed there was my idle and vacuum. The idle went up to about 1000 rpm and the vacuum went from -45 cmHg to -30 cmHg but the boost stayed about the same. I know that might be a little off subject but I was thinking that if I didn't have it hooked up right that might be a cause for the spiking. Just a thought.