How do you know the turbo is bad in a 1988 t-bird

Hello there and welcome to fixya

Turbocharger problems are some of the most difficult to troubleshoot. The main purpose of the turbocharger is to provide more air to the engine. The more air going into the engine the more fuel that can be burned, which results in an increase in horsepower. There are four main parts of the turbocharger: the wastegate, center rotating assembly, turbine housing and the compressor housing. By understanding how the turbocharger functions, it is possible to uncover the causes of problems.
Difficulty:Moderate Instructions

1. • 1 Check the air filter element as this is a main cause of blue exhaust smoke. This blue smoke occurs when there is not enough air going into the engine. Check all ducts and pipes for obstruction or leaks.
     
   • 2 Clean the turbocharger. Dirt that has caked onto the compressor wheel or the diffuser vanes can cause all types of problems. If the turbocharger is very dirty or the center housing contains sludge then you should also check the filters. Dirt coming in to the turbocharger is most likely due to broken filters.
     
   • 3 Check with the engine manual to ensure that the camshaft or pump is working at the correct timing. Adjustments may need to be made as the turbocharger can change over time. If the turbocharger is out of sync, then this will result in a noticeable decrease in engine power. An additional cause of decreased power is a gas leak in the exhaust manifold or the turbine outlet duct. The less gas the less power that is produced.
     
   • 4 Check the turbine blade and compressor for any damage such as indentations or notches. This type of damage will cause screeching noises, whining noises, rattling and scraping sounds. You will need to replace the turbocharger as well as locate the source of the damage to prevent further damage. There is a chance that the noises are due to other eternal components and not the turbocharger, but a visual inspection is easy to check before moving onto other components.
     
   • 5 Inspect the actuator if the entire turbocharger is frequently overboosting or underboosting. Make sure that the actuator is not loose and if so tighten it to the specified torque values. If there is visible damage to the actuator and air leak or if the actuator spring has broken a new actuator is needed.