not making boost all the sudden

27566 Views 15 Replies 8 Participants Last post by viper2788, Oct 20, 2013

viper2788

Discussion Starter · Sep 22, 2013 (Edited)

I was boosting around some backroads and all of the sudden there is a loss in power and the engine doesnt sound right. Theres no knock and I think the motor itself is fine, however its not boosting properly. I did one last WOT pull and the boost only measures 6psi as opposed to 16.5 like its supposed to. At idle it measures -7.5 instead of the usual 8.5-9.5psi.

The exhaust note is also different... pretty much the "rumble" is gone and its sounds higher pitched.

I have a clip of the exhaust

How it sounds now:
Boost problem - YouTube

How it sounded before:
2007 STi rev + 2 step launch control - YouTube

Theres no CEL and no error codes reading on the AP, but I feel like I'm making 1/5 of the power I used to have. I've check all of the hoses from the turbo to the TB but no problems there. From in cabin, it sounds quieter and raspy as rpms climb. seems my new "powerband" is between 2-3k rpms as it gets weaker as it climbs.

Car is an 07 STi with cobb axleback and stage1. Otherwise bone stock. Please help diagnose this! thanks.

1 - 16 of 16 Posts

MadRX

· #2 · Sep 22, 2013

Sounds to me like a boost leak. Have you checked your IC plumbing? A joiner/coupling may be loose/fallen off?

If it where something with the turbo, you would prolly have heard something give......

All the best with finding prob bro

STi Addict

· #3 · Sep 22, 2013

check for shaftplay

HeatSource

· #4 · Sep 22, 2013

yeah im thinkin boost leak... easy way to check if u dont have a smoker is to fill a spray bottle with a little dishsoap and some water. spray it around with the car running and look for foaming. my old turbo had shaft play, still pulled just as hard as before except it sounded like the dentists office.

STi Addict

· #5 · Sep 22, 2013

you need to check everything pre-turbo not after. Also loss of noise could be attributed to turbo not boosting properly which leads lot less air being combusted in the engine.

at last comment, when he's checking for shaftplay he'll have to check his intake route which hopefully may be the problem.

Madcow

· #6 · Sep 23, 2013

Sounds to me like a leak somewhere. I'm not sure if I agree with it being pre-turbo, as a pre-turbo leak is usually attributed to sketchy idle and AFR problems and not loss of pressure.

I would pull out your intercooler and look at the 90* elbow coming off the turbo. Also inspect the intercooler to intake coupler for any cracks or tears. These are the most likely culprits.

If you cant find any leaks, take your downpipe off and check for shaft play. Worn out journal bearings is definitely a possibility. If found early enough, you can get your turbo rebuild for a few hundred, and save yourself from blowing the turbo and having compressor wheel shrapnel potentially go through your motor (which happened to me).

STi Addict

· #7 · Sep 23, 2013

Madcow said:
Sounds to me like a leak somewhere. I'm not sure if I agree with it being pre-turbo, as a pre-turbo leak is usually attributed to sketchy idle and AFR problems and not loss of pressure.

I would pull out your intercooler and look at the 90* elbow coming off the turbo. Also inspect the intercooler to intake coupler for any cracks or tears. These are the most likely culprits.

If you cant find any leaks, take your downpipe off and check for shaft play. Worn out journal bearings is definitely a possibility. If found early enough, you can get your turbo rebuild for a few hundred, and save yourself from blowing the turbo and having compressor wheel shrapnel potentially go through your motor (which happened to me).

+1 to checking the Y-pipe, completely slipped my mind.

viper2788

Discussion Starter · #8 · Sep 23, 2013

Took it to andrewtech automotive today and they couldnt find the culprit after a quick inspection. It turns out all of my hoses are fine, including everything pre-turbo. Turbo itself also good. They suspect either an exhaust leak or a clogged downpipe. Unfortunately, they're completely booked until after the first week of october, but said I should be good to drive it carefully until then.

I'm actually hoping its a clogged DP so I can just replace it with a COBB and run stage2 while I'm at it. Anyway, thanks for the tips guys. I'll keep you posted.

Madcow

· #9 · Sep 24, 2013

A clogged downpipe? wtf? You may want to have them check your headlight fluid while you're at it.

Also you can't tell if the journal bearings in the turbo are worn out unless you take the downpipe off and check for shaft play which it sounds like they didnt do (or else their clogged downpipe theory would be proven im sure!)

An exhaust leak could be possible but it would have to be a large leak to get that low of boost, and the stock cast iron exhaust manifolds are known for their durability so I don't think it likely.

viper2788

Discussion Starter · #10 · Sep 24, 2013

Madcow said:
A clogged downpipe? wtf? You may want to have them check your headlight fluid while you're at it.

Also you can't tell if the journal bearings in the turbo are worn out unless you take the downpipe off and check for shaft play which it sounds like they didnt do (or else their clogged downpipe theory would be proven im sure!)

An exhaust leak could be possible but it would have to be a large leak to get that low of boost, and the stock cast iron exhaust manifolds are known for their durability so I don't think it likely.

Well "clogged cat" is the way he put it... As for the turbo, they used a wire camera through the intake to verify it spools during idle and keeps spinning as it should after the cars turned off.

But as I said, nothing is certain at this point. They did a very brief inspection and wont get around to actually working on the car until October.

spud majic

· #11 · Sep 24, 2013

my first guess is the car is in limp mode for it to make 6psi. IMO the biggest concern is the lack of vacuum at idle. i would get it checked for low compression. i noticed you had a small puff of what looked like blue(oil) smoke out the exhaust. you can also pull the oil fill cap and look for chuffing smoke coming out of the opening. if you dont see anything there you may also have a bent valve or maybe even a broken cam(i have heard of it happening but never witnessed first hand)

Madcow

· #12 · Sep 24, 2013

viper2788 said:
Well "clogged cat" is the way he put it... As for the turbo, they used a wire camera through the intake to verify it spools during idle and keeps spinning as it should after the cars turned off.

But as I said, nothing is certain at this point. They did a very brief inspection and wont get around to actually working on the car until October.

Ouch, sucks you have to wait until October.

That's good they put a camera on the compressor wheel and it looks okay. Doesn't rule out the exhaust turbine though.

Have you had any chance to log the vehicle? I'd be interested in seeing them to see if the car is just in limp mode for one reason or another.

Leftbehind126

· #13 · Sep 24, 2013

I don't trust visual checks for boost leaks anymore. Back when I had my STI, I had an issue where I could only hit 10psi and then it'd cut out. Didn't find the leak until we pressurized the system with air. I've found that just because it doesn't leak at idle, doesn't mean it won't leak at say, 5psi, or 10psi, etc.

Did they only do a visual inspection?

Also, I see bay tags. Where in MD are you? I'm in MD as well, so maybe I could help out.

viper2788

Discussion Starter · #14 · Sep 24, 2013

Madcow said:
Ouch, sucks you have to wait until October.

That's good they put a camera on the compressor wheel and it looks okay. Doesn't rule out the exhaust turbine though.

Have you had any chance to log the vehicle? I'd be interested in seeing them to see if the car is just in limp mode for one reason or another.

I've changed to tune back to stock since this has happened and problem still exists. That would rule out limp mode, right? Also, there werent any codes reading from the AP. Currently I've left my AP in a friends car and havent gotten it back. I wanted it out of my car when I walked into Subaru thinking I still have factory warranty, which ran out last year

I'll get it back shortly and try to do some logging in the meantime

Leftbehind126 said:
I don't trust visual checks for boost leaks anymore. Back when I had my STI, I had an issue where I could only hit 10psi and then it'd cut out. Didn't find the leak until we pressurized the system with air. I've found that just because it doesn't leak at idle, doesn't mean it won't leak at say, 5psi, or 10psi, etc.

Did they only do a visual inspection?

Also, I see bay tags. Where in MD are you? I'm in MD as well, so maybe I could help out.

I live in Gaithersburg(dc area). Any help would be greatly appreciated!

kelleyperformance

· #15 · Sep 24, 2013

hey, i have had a similar issue on my personal DD (08 STi). when the car was stock, it ran the 14.5ish PSI like expected... did full bolt on mods, still ran great. one day we decided to put an Acessport tuner with a custom tune we did into it. im an ASE master mechanic, and run a performance shop. so this stuff is not new to me... the car ran GREAT for a few days, then started running LOW boost, all the time. car ran perfectly, i mean PERFECT. ignition advance was dead on, A/F ratio was dead on, no CEL... commanded boost PSI was still correct, but actual boost levels were about 60%. commanding 20 or so PSI, it would run 12 psi. it was about as fast as a bone stock car when normally put down 320 AWHP... i checked EVERY single thing a mechanic could think of. of course the tune was the first thing, wasnt that.

could a clogged cat cause low power levels and reduced boost? absolutely. i dont think your turbo locked up or anything, sounds like you all verified that anyways. that cat may very well be your issue. hard to say from across the country lol... BUT it sounds very similar to the issue we had. our issue ended up being the OEM EBCS (boost control solenoid).

how did you come to the cat diagnosis again...? if you hit it with a rubber mallet, does it rattle or make any odd sounds? or sound hollow? if i can be of any help to you, your welcome to PM me. id be glad to help you. its one reason i like being on forums

John

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viper2788

Discussion Starter · #16 · Oct 20, 2013

It turned out to be a BADLY clogged cat. I got it replaced at Andrewtech with a new one and it runs great! Thanks for all the tips and advice :tup:

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