Final answer:
An unchanged compression reading after oil is added in a compression test indicates potential valve or head gasket issues rather than piston ring wear, guiding further diagnosis and repairs.
Step-by-step explanation:
When performing a compression test on an engine, if the compression does not increase after injecting oil into the cylinder, it often indicates a problem with the cylinder's valves or head gasket rather than the piston rings. Normally, adding oil temporarily seals the piston rings, and if compression increases, it suggests worn rings. However, when there's no change in compression after adding oil, the issue likely lies elsewhere, such as with the valves not sealing correctly or a compromised head gasket, both of which cannot be remedied by the presence of oil.
This finding is significant because it helps to diagnose the specific type of engine problem present. Since the compression test didn't result in increased pressure, the mechanic can rule out piston ring wear and instead focus on checking the integrity of the valve seals or the head gasket. Ignoring this could lead to inefficient engine performance or further damage.