johnson outboard diagnostic software download

The following steps are only general guidance.

In principle, the compression test is simple, but the many different types of outboards can add numerous important complexities. This also can help you determine whether an expensive teardown is needed. There are other diagnostic tests, such as a leak-down test, in which you measure the rate of air pressure leaking from a cylinder while the piston is in top-dead-center position. And even if you'd rather not attempt this yourself, understanding how the test works will let you evaluate what a mechanic tells you. Even if you're not a trained technician, you might be mechanically inclined enough to do this diagnostic test. The test measures how much pressure is built up by the motion of the piston inside the cylinder, given in pounds per square inch (PSI).

Without that transfer, the piston would grow in size from the heat and 'stick' inside the cylinder, causing damage.Ī compression check can indicate that the piston rings are working properly and that the cylinders are in good condition. In addition, if the rings aren't sealing properly against the cylinder walls, they're not doing another job of transferring the heat from the pistons to the cylinder walls. If the piston and rings can't compress the air-fuel mixture in the cylinder so the spark can ignite it, the engine won't run well, if at all. As the piston travels up and down in the cylinder, the piston rings seal against the cylinder wall so the air/fuel mixture can be compressed at the top of the cylinder on the upstroke.

An outboard gas engine needs air, fuel, spark, compression, and unobstructed exhaust - in the right amounts and at the right time.

Johnson outboard diagnostic software download