Turbos are creating vacuum instead of boost
03-16-23, 05:31 PM
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Turbos are creating vacuum instead of boost
I recently took my car apart to do the simplified sequential and silicon hoses. (It was already broke down for another reason) since I've taken it apart more and more issues are popping up. I think I've eliminated everything except for one problem. My turbos aren't making boost. I don't have a boost gauge on my car but I saw the flex pipe on the charge pipe collapse at 4500. And the car would struggle to get there. I assumed it would be the intercooler, but I took that out and cleaned it and that is not the issue. I put an external pressure/ vacuum gauge onto the y-pipe and started the car, and it seemed to run an okay amount of vacuum at idle. The issue is that whenever I give it gas the vacuum increases and I never reach boost. At WOT the turbo is pulling almost 25 in/hg of vacuum. If anyone has an idea of what would cause this please comment below. Thanks.
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DaveW (03-17-23)
03-17-23, 09:54 AM
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OK, a little 101 for ya.
Engines suck air in. You have a throttle body in the engine that restricts air going in to the engine. At idle, the throttle is BARELY open letting a tiny bit of air in. That creates a restriction, which means there is a measured vacuum between the throttle body and the engine.
In front of the throttle body should NEVER be vacuum. You need restriction for a vacuum. Yes, you can have minor restrictions, like a too-small paper air filter or something, but that is not measurable with a regular vacuum gauge.
And when I'm talking about a vacuum gauge, I mean one that measures in inches - the gauge you are using measures in in/Hg (inches of mercury) so there ya go.
All that said, you need to check for a MAJOR intake restriction. We are talking about a shop rag or towel stuck in the turbo, in the air box, something like that. That's the only way you can have THAT much restriction in front of the throttle body.
Remember this isn't even a turbo issue at this point - this would hold true with any engine and a non-turbo engine. You have something capped or clogged that should not be.
Post some pics up if you need more help!
Dale
Engines suck air in. You have a throttle body in the engine that restricts air going in to the engine. At idle, the throttle is BARELY open letting a tiny bit of air in. That creates a restriction, which means there is a measured vacuum between the throttle body and the engine.
In front of the throttle body should NEVER be vacuum. You need restriction for a vacuum. Yes, you can have minor restrictions, like a too-small paper air filter or something, but that is not measurable with a regular vacuum gauge.
And when I'm talking about a vacuum gauge, I mean one that measures in inches - the gauge you are using measures in in/Hg (inches of mercury) so there ya go.
All that said, you need to check for a MAJOR intake restriction. We are talking about a shop rag or towel stuck in the turbo, in the air box, something like that. That's the only way you can have THAT much restriction in front of the throttle body.
Remember this isn't even a turbo issue at this point - this would hold true with any engine and a non-turbo engine. You have something capped or clogged that should not be.
Post some pics up if you need more help!
Dale
The following users liked this post:
DaveW (03-17-23)
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