Check engine compression at specified cranking speed with engine at normal operating temperature, all spark plugs removed (on dual plugs, remove exhaust side only) and throttle wide open. Ensure crankcase is full and oil is correct viscosity. With compression gauge installed, use remote starter to crank engine.
Crank engine at least 5 revolutions, and record highest reading. Repeat procedure for all cylinders using approximately same number of revolutions. Lowest compression reading should not be less than 75 percent of highest compression reading. No cylinder compression reading should be less than 100 psi (7 kg/cm2 ).
COMPRESSION RATIO SPECIFICATIONS
Application. Compression Ratio
2.9L & 4.0L.9.0:1
EXHAUST SYSTEM BACKPRESSURE
Using a vacuum or pressure gauge, check exhaust system. Remove O[I2] sensor or air injection check valve (if equipped). Connect a 0-5 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 using a vacuum gauge, 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, check exhaust system for restrictions.
Monday, January 5th, 2009 AT 9:53 PM