Cylinder Test:

To find out which cylinder is the weakest, connect a vacuum gauge and tachometer to the engine. Run the engine at normal operating temperature; write down the indicator readings at idle. With the engine running disconnect the number one spark plug wire from the distributor cap (DANGER! take precautions to avoid being shocked). Once the plug wire is removed, write down the readings of the indicators. Replace the removed wire (DANGER! Take precautions to avoid being shocked). Continue removing each wire one at a time, writing down the indicator readings. Subtract each reading from the initial reading. The lowest reading would indicate the weakest cylinder, indicating that the cylinder is not contributing that much power.