I have a manual transmission mk6 GTI that I bought used with about 145,000 miles on it. I love this car, it's something I've wanted since I knew GTIs were a thing, and she came with a Cobb catback exhaust and intake. Her name is Fiona.*

But I've been having some trouble with her, and I think others may be able to learn from my experience. This post will be updated and edited as things happen, so be sure to check back.

It all started about five months ago. I got an inspection, and they said I needed tires. So I got some new tires and on my way home my car started running really bad. ECS and a blinking CEL. I drove her home, tried some things, and couldn't fix it. So I drove her to my mechanic who replaced the coil packs. He also said one of the cylinders was full of gasoline. (This is a clue that may become important later.)

Things were fine for a while, but I noticed she was having less power than normal. Eventually it got so bad that a Saturn Vue was able to outpace me from a stoplight. So I took her back to my mechanic.

He said "You need a new turbo. That'll be $3,100. And it's $1,900 for parts."

Me, being terminally online and an amateur mechanic, knew I could get a new turbo for under a grand (at the time) and felt confident enough that YouTube University could teach me how to do it myself.

So I did.

It was a few days of bloody knuckles, bruised ribs, hope and despair in equal measure, but I replaced the turbo myself. But when I took her on a test drive she still felt sluggish.

So I took her back to my mechanic. This made him pretty mad, and he didn't touch a thing and said "Check your work and go to the dealer."

I went home and checked my work. I found a small oil leak but nothing else out of the ordinary. Figuring that the dealer would have some fancy, proprietary software to tell me what the problem was I booked an appointment.

The dealer said "Your turbo is bad, you need a new one. That'll be $6,500 and $3,000 for parts."

Not happening.

One thing I noticed while the car was in pieces was a powdery white substance in the hot side of the turbo and the down pipe. I didn't think anything of it, figuring it was part of the smoke test my mechanic performed. But after some research I found that clogged catalytic convertors can cause the same powdery white residue.

Remember that clue from earlier? The gasoline in the cylinder? Well, that sort of thing is exactly what you need to clog a catalytic converter. If it gets blown into the exhaust.

And if you know how a turbo works you know that it needs fast exhaust gasses to produce boost. So if the exhaust is clogged it will look like the turbo is giving out when really it just can't spin fast enough.

So my next project is to install a 3" performance down pipe and a custom tune to see if that fixes my issue. Best case scenario is that it solves it. Worst case is that I'm ready to go to a K04 turbo. (Well, I might need a new intercooler.)

And the best part is that all of this - the turbo, the tools, the two trips to the mechanic, the downpipe, and the tune - will still be less than what my mechanic originally quoted just to replace the turbo.

Once I have the down pipe installed I'll post an update.

tl;dr - Sometimes a lack of boost is a problem with the exhaust system

* She's named Fiona because I found the COVID vaccine card from the previous owner in the glove box and his name is Scott. And Scotty doesn't know what Fiona and me get up to.