Checking Engine Vacuum

CHECKING ENGINE VACUUM
Manifold vacuum readings (taken at a vacuum port downstream of the throttle plate) should be steady and smooth. If valve damage has occurred the needle will rapidly fluctuate back and forth.

NOTE: Prior to checking vacuum, the ignition timing should be checked and adjusted. Ignition timing will affect the vacuum levels.

To verify valve, perform a compression check or leak down check on all cylinders. Cylinders with damaged valves will not develop compression and will not hold pressure.

If valve damage is detected the cylinder head will need to be removed.