Very low boost

[Null]

Hey guys, I have a 99 GST no mods really except an ACT2100. I just had my transmission worked on and my 5th gear replaced. Also before it went in when i was at around 3000rpm and would floor it the car would boost up to like 14psi and then shudder and shake like crazy until about 4000rpm. I thought this was a transmission issue but apparently not. Now that I have it back, it wont boost any higher than like 6psi, but no matter how hard I floor it I can't make it shudder like it did. Is this a boost leak, fuel system problem? What do you guys think? Thanks.

 

[sickfast2ndgen]

two things:

1. check to see if the vacuum/boost line is hooked up to your wastegate actuator.

2. check to see if the arm from the wastegate actuator is still connected to the flapper on the turbine housing.

A friend of mine had the wastegate arm come undone and the most he could manage was 2psi. i'm thinking you may be seeing a little bit more just because of the size of your t25.

as for the shuddering problem... i think it you need to provide a little more description.

 

[Null]

Ok, I will check the wastegate in the morning. As for the shuddering, it doesn't seem to happen in 1st gear at all (probably because its very hard to build full boost in such a light gear). in 2nd-5th if I am going say... 30mph @ 2000~ rpm in 3rd and I push the pedal to the floor, the boost (before the 6psi problem) would spool up to 13psi or so and then the needle and car would start shaking and the acceleration became much slower, once it got to 3500rpm or so the boost would hit 14-15 steady and the car would continue to accelerate properly. It only seems to occur at low rpms, once you hit 3500 or so it seems to be fine in any gear.

 

[sickfast2ndgen]

sounds to me like you're experiencing the boost control solonoid flicker. it happens between 2300 and 3900 RPMs with the intent of removing that feeling of boost coming on hard all at once. they did it to keep the car from scaring the crap out of old folks when it spooled up.

I have never really heard of the problem limiting the performance of the car though. perhaps your BCS is bad and when it tries to flicker it bleeds off too much pressure. that's just an idea, and again, i have nothing to back it up with, but it may be worth your time to make a home depot boost controller, install it (removing your BCS in the process) and see if your problem goes away.

 

[oldman]

Boost leak test is one of DSM's best friend.

 

[sickfast2ndgen]

Boost leak test is one of DSM's best friend.

roger that.