got my 105k maintenance done (along with timing and drive belts, all pulleys in the front, lower radiator hose which had a leak in it), and I've been experiencing low boost. I've been tracking it on my AP, and it is only hitting around 8.5-9 psi max. They checked the turbo while they were in there, and said that it looked good with no shaft play. Also checked all the lines. They (dealership) thought it might be the downpipe seals (replaced), and didn't help. They think that I may have a cat that disintegrated in the DP. If so, looks like I'll be in the market for a new downpipe. Grimmspeed has theirs on backorder atm, leaning towards that over Cobb, considering it's also about 200 bucks cheaper. Gotta love it when regular maintenance turns into forcing me to put performance mods on my car! Anyhoot, any other ideas why I may be having low boost? They said that on throttle the boost was dipping into vacuum before climbing. They were supposed to email me their full notes, so I'll have to call them back and have them resend it.
Check the vacuum lines for the boost controller. Is it a stock boost controller? Sounds like you’re only getting wastegate pressure. Does the exhaust sound different/plugged? I’d guess it’s something upstream of the turbo and keep looking for hoses that may be loose or cracked or reinstalled incorrectly.
Would a disintegrated cat cause that? I don't know that that would effect anything in terms of boost? Possibly an exhaust leak on the engine side of the turbo (headers/up pipe)? Other than than, possibly a leak around the wastegate? What year/model do you have? Is it the stock turbo?
It's a 2010 FXT with stock TD04 with the stock boost controller. Only thing I have on it is an STi exhaust, but the low boost was happening before that. I'm running the AP Stage 1 map, then downloaded the high wastegate map that they have on there with no changes. They said they checked all the lines, and said that if the cat was disintegrating, some chunks could block flow and cause backpressure. Reading more said that the BCS could be on its way out too, so just gotta save up some moolah for some upgrades.
When I got my first boosted Subaru, an '03 WRX (probably 10 years ago now, yikes), it was behaving similarly to what you're describing - 9psi max. I found that at some point the wastegate vacuum lines had been swapped out. The problem with that is that there is a little restrictor pill that is supposed to be in the vac line off the turbo compressor housing before the T. Mine was missing the pill - got the hose with the pill and problem solved. A quick search directed me to this thread where there is some discussion on the topic and decent pictures. Squeeze the vac line that comes off the turbo compressor housing and see if you can feel a bump in the hose http://www.perth-wrx.com/vb/mechanicals/48287-restrictor-pill-what-why-you-need.html
