I have a 1998 a4 1.8t 5 spd. It has a gt28 garret turbo on it that makes 23 on boost. Upgraded intake, injectors and for other things. It has been running great but the other day the boost started maxing out before redline. In first gear it seems do great. Second gear does fine about half the time but third gear all the way up to fifth the boost will max out around 4500rpm and once it gets closer to redline sometimes it starts cutting out slightly. Lightly enough that it can barely be felt sometimes. I've checked everything I can think of but am new to the turbo world. Any help would be greatly appreciated.

 

Things to check is if there is a flow restriction, also might want to check the turbo itself to see if there is damage to the compressor wheel or exhaust wheel. I had the same issue with my GT35r pushing 32+psi in 4th gear when racing at high elevation, turned out to be my HKS air filter was not allowing enough air thru it and was causing the turbo to starve for air which caused the boost to drop at 6k rpm.

 

kinda seems like a boost leak to me. if you can, pressure test your charge piping

 

Thanks guys. I'll check for any leaks tomorrow. If it was a leak on the intake side of the turbo it would be low boost correct? Since its over boosting there's a good chance its could be starving for air or there is a leak on the exhaust side?

 

what? a leak on the intake side of the turbo will not effect boost really, and you never mentioned it was overboosting before. you said it would taper off

 

My mistake on the over boosting. Its not. I meant hitting max at a lower rpm then it use to. I never said it tapers off. The motor will cut out some after the turbo hits Max and the rpms try to climb. I mean a leak from the intercooler side affecting boost. I have noticed the car back firing of I shift early. Just driving it normally and shifting around 3-3500. I couldn't find any leaks anywhere. Did notice the flex joint in the exhaust that's about 2 feet down the exhaust from the turbo is leaking pretty bad. Like I said this is my first turbo car and I'm learning. Just throwing anything I find wrong out there. The Wastegate seems to be working.

 

how dd you look for leaks?

 

Pressure tested the system

 

How much it.cost.you ro put togther the gt28? plan on doin one.for.my a4 in near.future

 

No clue. It came with it on it. He knew less then me about it apparently because he said it was a k04 and it's not