Boost problems

[Steveinabox]

I have a 91 Tsi with the only mod being a 3 inch catback, downpipe, testpipe, about two days ago i drove to work and when i went to leave work that night i noticed my boost was shooting up from 10psi at about 4000rpm and reaching about 17 or 18 psi at just over 5, it looked as though it would still climb but out of fear of damage i did not try to push it beyond and would let off the gas, it did this for the past two days until this morning when i took the car for a drive and could barley achieve any boost at all in first gear and at most could achieve 10 psi in second but not until almost 5000 rpm would the turbo boost start to boost and when it started it would boost up to 10psi at a very very slow pace.....if anybody has any input on what this could be i would greatly appreciate it....thanks

 

[GTM]

Originally posted by Steveinabox
...

i noticed my boost was shooting up from 10psi at about 4000rpm and reaching about 17 or 18 psi at just over 5, it looked as though it would still climb but out of fear of damage i did not try to push it beyond
...

I know all your focus was suddenly on the gauge but how was the car performing? If it was accelerating normal for those throttle settings then I would become suspicious that the sending unit or gauge is malfunctioning.

Look under the hood for hoses having come off or damaged. Especially the waste gate actuator or the selonoid valve which controls when it is supposed to open. I know there are other possibilities but it's getting late and me 'ead ain't working so good.

Hopefully someone else can fill in the blanks.

Cheers,
GTM

Cheers,
GTM

 

[Steveinabox]

I had it in on the shop a few days ago when it was overboosting and everything was checked over that could have been without taking apart the the turbo and manifold and what not...the gauge is running acurate as well as the solenoid...right now my only other option is to take apart the turbo which is something i want to avoid...

 

[GTM]

Originally posted by Steveinabox
I had it in on the shop a few days ago when it was overboosting and everything was checked over that could have been without taking apart the the turbo and manifold and what not...the gauge is running acurate as well as the solenoid...right now my only other option is to take apart the turbo which is something i want to avoid...

You didn't mention if you had actually lost or gained power during those events???

This could be a symptom of the turbo bearings (bushings) impending failure. A drop in oil pressure, air mixed in with the pressure oil could cause the turbine to spin up more freely until they failed by seizing and thus become more sluggish or not rotate at all. This is a tactile judgment call which only knowing how something should rotate and behave that is difficult to put into words. I can't in good conscience tell you to replace the turbo for I don't have enough info to isolate that as the cause.

I have mentioned in the past using a canister type vaccum cleaner where you can get a good air stream on suction and exhaust can you then get the turbine to spin in an approximate running condition. Remember that you will have no oil feed lube and any prolong testing should be done with an occasional running of the engine to fill the oil pipe. There are just so many variables here including climate change and oil viscosity, low oil level, etc. I can't be more specific. You or a hands on professional are the only way of tracking this down though there may be someone here who has had this exact condition and can share their findings.

Cheers,
GTM