Mechanical Inspection

CAUTION: DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter to crank engine. Fuel injectors on many models are triggered by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine's oiling system.

Testing Compression

1) Disconnect the BAT terminal from the HEI distributor or ignition module. Check compression pressure with engine at normal operating temperature, all spark plugs removed and throttle valve wide open.

2) Insert a recording type compression gauge and crank each cylinder through 4 or 5 compression strokes. The lowest reading should not be less than 100 psi (7.03 Kg/cm² ). If compression builds up quickly and evenly to specified range on each cylinder, compression is normal.

Exhaust System Backpressure

The exhaust system can be checked with a vacuum or pressure gauge. Remove O2 sensor or air injection check valve (if equipped). Connect a 1-10 psi pressure gauge and run engine at 2500 RPM. If exhaust system backpressure is greater than 1 3/4-2 psi, exhaust system or catalytic converter is plugged.

If a vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.