Thread: What's going on with my boost?

So... after a night at Sac Raceway... I realized that my boost fluctuates alittle TOO much!!! When I'm just driving around town or on the freeway normally... my boost is usually fine, goes up to 15psi and stays there til I let off the throttle. But, I can recall a couple of times when I was racing around town or on the freeway giving WOT through all my gears, my boost doesn't go all the way to 15psi. It usually sticks around 12-13psi... sometimes more sometimes less. Well on my way to Sac Raceway I double checked that my boost is where I want it at and It was holding 15psi steadily. On the track, it was a different story though. Through first gear, it would hit somewhere between 14-15psi, but as soon as I switched to second gear... no more than 12psi, third gear 11-12psi and so on... So I decided to crank up the boost alittle... next run same thing happened, boost kept going down with every gear. Turned the boost up alittle more... exact same results...11-12psi. Left the track and was on my way home...solid 18psi. WHY? :x I could've been in the 14's tonight if it wasn't for that!!! http://sacramento-dsm.com/viewtopic.php?t=258

Sounds to me like 1 of 3 things. Boost leak, Wastegate flapper, or O2 housing.

If you have a boost leak somewhere, it will give you inconsistant boost readings. Hoses are made of rubber, so they will contract and expand depending on how hot the car gets. Thus the fluctuating boost. I would think you had a possible leak since you just installed the starion fmic.

If it's the wastegate flapper, signs would be no matter how high you turn the boost up, it won't go any higher then a given point even after checking and fixing all your boost leaks. This can be caused by a wearing flapper, a crack through the turbo housing running through the wastegate passage, or a bad gate arm.

Your O2 housing can have a crack in it or be leaking through the turbo-to-o2 gasket. 1G stuff is known for cracking. This should be fairly easy to diagnose since you would see/feel the exhaust gases escaping, leaving a black trail usually.

While you try to diagnose it, I don't remember if you said you had a fuel pump and injectors or not...but I would stay away the 14psi and greater area til you get it fixed. Turbos run 2x as hard to get to 15psi if you have a leak or faulty gate. Have you logged your car since?

Originally Posted by mygst95

Sounds to me like 1 of 3 things. Boost leak, Wastegate flapper, or O2 housing.

If you have a boost leak somewhere, it will give you inconsistant boost readings. Hoses are made of rubber, so they will contract and expand depending on how hot the car gets. Thus the fluctuating boost. I would think you had a possible leak since you just installed the starion fmic.

If it's the wastegate flapper, signs would be no matter how high you turn the boost up, it won't go any higher then a given point even after checking and fixing all your boost leaks. This can be caused by a wearing flapper, a crack through the turbo housing running through the wastegate passage, or a bad gate arm.

Your O2 housing can have a crack in it or be leaking through the turbo-to-o2 gasket. 1G stuff is known for cracking. This should be fairly easy to diagnose since you would see/feel the exhaust gases escaping, leaving a black trail usually.

While you try to diagnose it, I don't remember if you said you had a fuel pump and injectors or not...but I would stay away the 14psi and greater area til you get it fixed. Turbos run 2x as hard to get to 15psi if you have a leak or faulty gate. Have you logged your car since?

Yeah, boost leak sounds possible. Gotta check that out next time I'm in the shop.
I doubt it's the wastegate flapper, if you say boost won't go higher than a given point, cause I can still play with the boost controler and it responds just fine when I'm not racing around.
O2 housing crack seems very possible as well. Stock 1g O2 housing made 14 years ago and abused for 138k.... probably has a few cracks! That's my next plan for the car... gotta start working on exhaust and all it's components. I'm gonna be in the market for 2g manifold and O2 housing once I find some more cash.
My turbo has seen better days as well... spools pretty slow but still has a nice kick to it.
And I'm running stock fuel punp and stock injectors.


Never mind... Don't listen to me... I'm a dumbass and don't know sh!t about DSM's... just talked to a friend on the phone and he said it's most likely the wastegate flapper.

this problem sounds familiar. :o

I put washers between the wastegate actuator and compressor housing and swaped boost controllers... boosts better than ever now :P got lucky this time... nothing to serious