Question

when testing intake manifold vacuum, the gauge reads normal at idle, but reads very low when the engine is held steady at 2,500 rpm. technician a says this indicates worn valve guides. technician b says this indicates a restricted exhaust system. who is correct? select one: a. technician a b. technician b c. both a and b d. neither a nor b

Explanation:

• Worn valve guides would cause a vacuum gauge to fluctuate at idle, not just have low vacuum at higher RPM.
• A restricted exhaust system causes back - pressure. At idle, the engine may still draw enough vacuum as the flow is low. But at higher RPM (2500 rpm), the restricted exhaust limits the engine's ability to expel exhaust gases. This leads to a build - up of pressure in the exhaust manifold, which in turn reduces the intake manifold vacuum.

Answer:

b. Technician B