How to test if turbo is properly working in a 2006 Forester XT

Question

I recently had my Forester engine serviced and afterwards it didn't feel like I was getting boost and was getting a whirring/spinning noise while throttling.  I brought it back and they realized they left some loose turbo vacuum hoses.  They put them back on and it's not making the noises anymore but I think it still doesn't feel like there's a lot of boost - at least not like before.  They test drove it with me and say it does feel like there's some boost at the high end, but I certainly am not feeling the boost when I'm merging on the highway or hitting the throttle.

At this point, it's just seat of butt testing to know what's going on - is there a more definitive way I can diagnose whether I'm getting the proper turbo boost - or at least that the turbo boost is working at all - as a non-mechanic?  Something I can point at and say yes/no it is working before I take it back to the mechanic?

Drewster · Answer

Without data, your diagnosis is about the best you can do. A poorly operating (or installed) turbo won't make as much boost (which you can feel), and they usually sound terrible when the turbo actually fails. In short, your senses are your best bet if you don't have tools to get data. Generally things are pretty bad by the time you see a check engine light.

If you're looking to do something to get data, I highly recommend an Accessport, especially if we're talking about a turbocharged Subaru. It can tune the car, read trouble codes, and even if you don't want to make a whole lot of power, datalogging can tell you if the car is making substantially less load (what the computer cares about rather than boost), if a cylinder is misfiring, or if the engine is running on the lean side.. loads of information.

How to test if turbo is properly working in a 2006 Forester XT

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