Repeat the test on the remaining cylinders. If the lowest cylinder pressure is 15% less than the highest cylinder pressure, go to next step. If the cylinders are within 15% of each other the compression is within tolerances.7. A compression test will verify the compression of the engine and diagnose low compression.
Instructions
1. Start the engine and allow it to idle for a few minutes to warm it up. It isn't necessary for the engine to be at operating temperature, it only needs to be warm. Turn the engine off.
2. Remove all four spark plug wires from the spark plugs. Grasp the plug wire boots with the spark plug wire pliers and twist the boot while pulling the wire off the spark plug. The Two thousand one Ford Focus is a front-wheel drive vehicle with a transverse mounted four cylinder engine. The spark plugs are located on the side of the motor, facing the front of the engine compartment, and are easily accessible.
3. Unscrew all four spark plugs using a 5/8-inch spark plug socket, extension, and ratchet. Remove the fuel pump fuse from the auxiliary fuse box located in the engine compartment between the firewall and the air filter housing. In the Two thousand one Focus the fuel pump fuse is in position number Twelve as marked on the fuse box cover. This will prevent fuel from being supplied to the injectors during the test and prevent the possibility for an engine fire.
4. Block the throttle open by using a weight, or other suitable object, to fully depress the throttle pedal. Screw the hose from the compression tester into the number one cylinder spark plug hole. In the Focus are numbered from left to right. Plug the compression tester gauge onto the hose.
5. Turn the ignition key to the start position and listen to the engine. As the pistons travel up through their compression stroke it will slow during the compression stroke of the cylinder with the compression tester installed causing an audible change in the sound of the engine. Crank the engine six revolutions and observe the pressure shown on the compression tester.
6.
As the pistons in the engine of your Two thousand one Ford Seat measure up in the cylinder, during the compression stroke, they compress the air/fuel mix. This causes the concoction to heat up to slightly below the self-ignition temperature of the fuel. Even-handed before the piston reaches top dead centre of the stroke the spark plug fires and ignites the fuel. As the engine wears, compression is forfeit and may misfire whether the fuel isn't heated Sufficiently during the compression stroke.Perform a "Wet" compression test on the lowest cylinder. Add a tablespoon of oil into the cylinder with the lowest compression and reinstall the compression tester. Crank the engine for six revolutions and observe the pressure on the gauge. If the pressure increases, more than a few psi, during the wet test the piston rings are worn out. If the pressure remains the same the valves are not sealing properly.
