solving electrical issues in vehicles

How To Diagnose Turbocharger Issues When You're Test Driving A Used Sports Car

by Cherly Fowler

Turbocharged engines and sports cars go hand in hand. When fitted with a turbo system, an engine is able to produce the same amount of power as an engine with much higher displacement. However, turbo systems are also highly complex. If you're considering a used sports car with a turbocharged engine, it's important to diagnose any issues with the turbo system before you make the purchase.

Diagnosing Vacuum Leaks

Turbo systems require a complex series of intercooler pipes and vacuum lines that connect the turbocharger to the engine's intake manifold. The rubber vacuum lines and gaskets between separate sections of piping are common culprits for air leaks. Vacuum leaks will cause the engine to produce less power and deliver reduced fuel economy, so it's important to ensure the used car you're considering has an airtight intake system.

When you test drive the vehicle, let the engine warm up completely. As it warms up, the engine's idle speed will slowly decrease and settle somewhere below 1,000 rpm. Once it does, pay close attention to the tachometer. Vacuum leaks will cause the engine to idle inconsistently — the tachometer needle will bounce up and down as the engine tries to compensate for the inconsistent airflow passing through the throttle body. In contrast, a healthy turbo system that's free of leaks will idle smoothly at a consistent rpm speed.

Rev the engine a few times with the car in neutral. If there are no vacuum leaks, the engine will rev up and fall smoothly back down to its idle speed. Vacuum leaks will cause the engine to fall below its idle speed after revving, and it will likely sputter as the engine tries to keep itself from stalling.

Diagnosing Issues with the Turbocharger

Now it's time to take the car out on the road so you can really test out the turbocharger. When you accelerate at full throttle, the turbo will produce its maximum amount of boost pressure. Glance at the boost gauge to make sure the turbo produces a smooth and consistent amount of pressure. The boost gauge should quickly rise to the turbocharger's peak amount of pressure, then smoothly fall a bit as the engine approaches its rpm redline. If the boost gauge needle spikes up and down as you accelerate, the car likely has a boost leak. Boost leaks lead to reduced horsepower and can cause numerous reliability issues with the engine.

When you accelerate, listen closely to the noise that the turbocharger produces. The turbo should produce a high-pitched whooshing sound as the compressor spools up and sucks in air. However, if you additionally hear a metallic whining noise, there are likely some issues with the turbocharger. Worn-out bearings are a common culprit — friction within the bearings produces the metallic whine, and the bearings will be prone to failure at any moment. If you hear a harsher metallic grinding noise coming from the turbocharger, the bearings are likely so worn out that the compressor wheel is scraping the inside of the turbocharger housing. If that's the case, the entire turbo charger will likely need to be replaced.

There are a myriad of mechanical issues you should look out for when shopping for a used sports car. However, if the car you're considering exhibits none of the above issues, you can at least rest assured that the car's turbocharger system is in good working order. For more information, contact a use car sales company like Car Craft Auto Sales, Inc.