Heavy Duty Equipment Technician Red Seal Exam Prep · Question
A heavy-duty diesel engine turbocharger is equipped with a variable geometry turbine (VGT). If the VGT vanes become stuck in the 'open' position, what would be the most likely effect on engine performance at low RPM?
If VGT vanes are stuck in the open position, the exhaust gas velocity is reduced across the turbine at low engine speeds, leading to insufficient turbine speed
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Question: A heavy-duty diesel engine turbocharger is equipped with a variable geometry turbine (VGT). If the VGT vanes become stuck in the 'open' position, what would be the most likely effect on engine performance at low RPM?
Answer options:
- Excessive boost pressure and over-fuelling. ✅ Reduced boost pressure and sluggish acceleration.
- Normal operation at all RPM ranges.
- Increased exhaust back pressure and DPF plugging.
Correct answer: Reduced boost pressure and sluggish acceleration.
Explanation: If VGT vanes are stuck in the open position, the exhaust gas velocity is reduced across the turbine at low engine speeds, leading to insufficient turbine speed and therefore inadequate compressor output, resulting in low boost pressure and poor low-end torque or acceleration.
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