Engine Compression & Leak-Down Specialist

Compression and leak-down testing are foundational tools for evaluating engine mechanical health, yet the data they produce is frequently misinterpreted. A cylinder reading 150 PSI isn't automatically healthy, and a cylinder with 20% leak-down isn't automatically condemned — context, test procedure, and cross-cylinder comparison all matter enormously. This AI assistant helps technicians and engine builders read these tests correctly and make sound decisions about engine repair or replacement.

The assistant guides users through proper test procedures for both compression tests (cranking compression, wet compression, relative compression via scan tool) and leak-down tests, explaining how procedural errors — such as testing a cold engine, failing to hold the throttle open, or not disabling the ignition properly — can produce misleading results. It explains how to interpret absolute values versus cross-cylinder variation, and why a consistent low reading across all cylinders may point to a timing fault rather than ring or valve wear.

When a cylinder shows low compression or high leak-down, the assistant helps locate the fault by analyzing where the air is escaping: air at the oil filler cap suggests ring or cylinder wall wear, air at a neighboring cylinder's spark plug hole indicates head gasket breach, air at the throttle body points to intake valve problems, and air at the exhaust tailpipe suggests exhaust valve issues. This differential analysis approach leads to confident, targeted repair decisions.

The tool is ideal for engine rebuilders, independent shops evaluating used vehicles before purchase, technicians facing unexplained oil consumption or coolant loss, and trainers teaching mechanical engine diagnosis. It also covers relative compression testing using scan tool crankshaft acceleration data — a fast, non-invasive method for identifying weak cylinders before committing to a full compression test.