Zero or Negative boost

[4GTSiMAN63]

I bought a 92 TSi about 2 weeks ago, got it for a good price. The car idles good meaning it sound fine, but when you rev it up to anywhere past idle(1k) the boost guage moves to about 0 and below. when the car is at idle the boost guage is at -7. I dont think this is right, But I am novice when it comes to turbo cars/DSM. I took out the turbo and the very very little shaft play. I just wanted to run this thru the forum before I go out and buy alot of stuff I don't need, my goal right now is to get the car up and running. After that I am going to do a full tune up before modding it. I an going to try and post a pic.

 

[2002SL1]

That is perfectly normal at idle. The "negative Boost" is acctually called vacume, every gas engine car will produce it at Idle and the Gauge will move up to 0 as soon as you hit the gas because it is no longer making vacume. The turbo on the car will need a little RPM and time to accutally spool up to make boost. But yeah there is nothing wrong witht the car.

 

[xioca]

Be sure to get a good aftermarket boost gauge, cause you can not rely on that stock one what so ever. Also you shouldn't be able to build boost free reving your car, maybe 1 or 2 psi but that varies. So you've owned the car 2 weeks and haven't driven it yet... whats broke?

 

[4GTSiMAN63]

Well, the past owner told me that the car sputters when driving. When he started it before I bought it, there was black smoke coming from the exhaust. So I bought the car and towed it home and started it again to see if I can find out whats wrong with it. It didn't smoke the black smoke after I got it home. It only smoked when i reved it high, around 4-5K. The smoke color was a light blue and it was coming from the exhaust and engine bay. I haven't driven the car since towing it home because I have no tags. Thanks for your replies

 

[drewbe121212]

Hmm yeah he is correct with the boost. That is correct, however get a new gauge for the boost. That gauge uses the ecu and it tries to "guess" what the amount of boost being pushed is.

The black smoke may be caused by running to rich... then again maybe not.

 

[forcefed4]

Blue smoke = burning oil.
Black smoke = rich.

If you have smoke in the engine bay you have some kind of exhaust leak. You might check for a crack in the exhaust manifold or the turbine housing. If you're lucky, it might just be a gasket. You could have leaking valve seals causing the burning oil, or your turbo is going, or it might be something else. You might consider doing a compression check. For the black smoke, build yourself a boost leak tester and see if anything is leaking. If there is, that could be the cause of that and the sputtering while driving.

 

[MrBoxx]

Replace the spark plugs with NGK BPR6ES, gapped at .028".

Do a boost leak test.

Do a compression test, and if necessary, a leak-down test.

Check every hose for leaks.

Check your in/out shaft play as well as side/side and up/down shaft play on the turbo.

Keep an eye on the oil and coolant levels.

 

[MyÜberFastGSX]

The negative boost is called vacuum. At idle, a car should produce about 20hg. When revving, you shouldn't see more than 5psi of boost. This is because there is no load on the turbo causing it to spool.

 

[spyderturbo007]

Replace the spark plugs with NGK BPR6ES, gapped at .028".

Do a boost leak test.

Do a compression test, and if necessary, a leak-down test.

Check every hose for leaks.

Check your in/out shaft play as well as side/side and up/down shaft play on the turbo.

Keep an eye on the oil and coolant levels.

Looks like you need gas too.

 

[twicks69]

Along with the list of "things to do" above, check the MAF for damage or obstructions, check the air filter, check the O2 sensor and the knock sensor, and CHECK YOUR TIMING.

It sounds like you have an oil leak (gasket, oil feed line leaking, oil return line leaking, valve cover gasket, cam seals, etc -- check them all.), along with either worn piston rings or worn valve seals, from your "blue smoke".

If you are one tooth off on your belt, you will have problems.