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Boost Stuck at 10 PSI

279 Views 6 Replies 4 Participants Last post by  pocketdrummer
While driving to work today, I noticed that I didn't have quite the power I'm used to having, and it looks like I'm only getting 10 PSI of boost. If I'm in neutral and hold the RPMs at 2k for a little bit and let off, I get a pop from the exhaust. Also, every could seconds while it's idling, I'll have a short slightly louder rumble. Almost like a single ignition stroke was a little more audible than the rest.

The car has about 140k miles on it, and I have the following parts:
  • Cobb Turboback Exhaust
  • Samco Intercooler Hose Kit
  • Silicone Vacuum hoses going to/from the stock BCS except for the one with the pill.
  • XPT Tuning OTS Tune (open source)
I've also been losing a decent amount of oil. I do have leaks at basically every point of the AOS (I probably need to replace all of the hoses), and I have other leaks elsewhere around the engine, but I'm not sure if the losses are due to that or if I'm burning oil. I don't have any blue smoke at the moment.

What might be causing this?
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A lot could be causing that. Step 1 - fix all your oil leaks and get a compression test done.

step 2 - dependent on step 1 results.
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Update: Everything is "back to normal" now, but I don't trust it. I drove home gingerly for the first half and then tried it again, and boost came back up to ~17 psi.

About the oil, I took it into a shop the Raincity Subies facebook group recommended when I lived in Seattle, and they basically told me a compression and leak down test would be a waste of money. "Given the mileage, it's probably just worn out. As long as you keep topping up the oil, you'll be fine. If you get tired of doing that, we can replace your short block."

I'm definitely going to take care of the leaks, but right now I'm trying to triage. I'm going to try to run a few logs as soon as I get the opportunity and see if I'm getting a lot of knock, and then when I get a chance, I'm going to take it to MZM and see if they can diagnose the issue.
Surprised they told you that would be a waste. When it’ll tell you the health of your motor. Being low on oil shouldn’t cause you to drop boost that much. Af a minimum it should be a log by the shop to see what’s going on. I’d definitely go somewhere else based on that info.
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I the AOS installed properly should be the first question?

Assuming the AOS is installed properly, doing the compression and leak-down tests, will tell you whether or not to to fix the leaks immediately, or as part of a rebuild also sooner than later. It will also indicate a single cylinder issue such as a cracked ringland rather than wear. If you drive it till you get metal in the oil from running it low or bit of piston or worse, you'll need more parts than a SB.
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Sounds like they didn't want to get involved.
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Well, we officially have a problem...

I haven't made it to the shop yet (it's been running fine so far, and I haven't had time), but I found my Tactrix, so I tried to run a log. Unfortunately, it didn't actually log the run when I hit defrost (maybe there's a setting I forgot somewhere to make it do that).

In a nutshell, it registered -1 feedback knock, and -5 fine learning knock. IAM is down to zero. Now I'm stuck at only 10psi of boost again. I really wish it logged the actual run. At this point if it goes back to 1.0 IAM, I'm scared to test it again.

On a scale from 0 - F, how F'd am I? Is there any chance this is something other than an engine going out?

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