Why is sealing at the joints in the inlet manifold important?

• A. It prevents water ingress.
• B. Any leak will allow ambient air to enter and weaken the mixture, leading to rough running, overheating and possibly detonation.
• C. It reduces backfire.
• D. It improves fuel economy.

Answer: (B)

The essential idea is that the intake system must deliver a precisely measured air amount to the engine. If the joints in the inlet manifold aren’t sealed, ambient air can leak in without passing through the sensors and metering system. That unmetered air changes the air–fuel ratio, typically making it leaner than intended. A lean mixture burns hotter and can cause rough running, higher operating temperatures, and even detonation under certain conditions. Keeping the joints sealed ensures the fuel-air mixture remains within the figures the engine control system was designed to achieve, which smooths idle and running and helps prevent overheating and knock. Water ingress, backfiring, and fuel economy aren’t the primary effects of these seals, and leaks generally don’t improve efficiency.