Question

during a running compression test, a cylinder rises to about 80% of the cranking compression pressure when the throttle is snapped to wide open. technician a says this may indicate a worn camshaft lobe. technician b says this may indicate excessive carbon buildup. who is correct? select one: a. technician a b. technician b c. both a and b d. neither a nor b

Explanation:

• A worn camshaft lobe can cause issues with valve timing and lift, which can affect compression. When the throttle is snapped open, the engine's air - fuel mixture requirements change, and a worn camshaft lobe may not allow the valves to operate correctly, potentially leading to the described compression issue.
• Excessive carbon buildup on valves or piston crowns can also affect compression. Carbon buildup can change the combustion chamber volume and valve sealing. When the throttle is opened suddenly, the altered geometry due to carbon buildup can cause the compression to rise to a lower percentage (80% in this case) compared to cranking compression.

Answer:

C. Both A and B