Just had an interesting little issue today I'd like to share with you guys.

One of our customers took out his transmission and brought it in to us to install some RA gears. Once it was finished, he picked it up and he and his friend installed it back into the car. A few days later he calls up and says that his boost is now lower and the car is running very rich. I told him that this was most likely a boost leak and to check around for loose clamps and such. He didn't find anything right off the bat so he took the car to another Subaru shop that is much closer to to where he lives for a quick inspection. At that shop, he was told that he clearly didn't have any boost leaks but the car was just running rich and should be re-tuned. He then decided to bring the car back in to us today to verify the diagnosis.

I hopped in the car with a laptop and as soon as I connected to the ECU, I could see the fuel trims were maxed out on the negative side. After a quick drive, I could also see that his WOT a/f was pegging the wideband rich (bellow 10:1) and the turbo was spooling up slowly. These are all classic text book symptoms of a significant boost leak and by the look of the fuel trims, the majority of the leak would have to be localized between the turbo and throttle body. Combine this with the fact that the customer just pulled and re-installed the TMIC, and the problem should be very clear to anyone with any trouble shooting or tuning experience.

So after the initial diagnostics, I was 99% sure there was a significant leak between the throttle body and turbo. So we pulled the car in and performed a boost leak test by pressurizing the intake tract. We found one of the TMIC clamps was damaged and not holding the coupler tight, the BOV gasket was damaged and leaking, the BOV adjustment screw was leaking, and the boost gauge line was cracked and leaking as well. We fixed all the leaks, verified that there were no others, and took the car out again for a test run. Now the a/f and boost levels were exactly on target as they were tuned originally and the fuel trims were back near 0% where they should be as well.

The moral of the story is be very careful when working on your car or letting friends work on your car. Always verify your work by testing for leaks any time major components have been off the car. And finally, be very careful about who trouble shoots your car and what they may be trying to sell you.

Thanks
-- Ed