Final answer:
The pressure should build from 85 to 100 psi within a certain time frame when the engine is at operating rpms.
Step-by-step explanation:
When the engine is at operating rpms, the pressure should build from 85 to 100 psi within a certain time frame. The specific time frame can vary depending on the engine and its design.
For example, let's say the engine is designed to reach 100 psi within 10 seconds. This means that when the engine is running at its operating rpms, the pressure should increase from 85 psi to 100 psi within 10 seconds.
It's important for the pressure to build within a reasonable time frame because it ensures that the engine is performing optimally and that all the necessary components are functioning correctly.