3306C Truck Engine Caterpillar

An engine that runs rough can have a leak at the valves. An engine that runs rough can also have valves that need an adjustment. Use the following test for a quick, easy method to identify a cylinder with low compression. This test will also indicate whether a cylinder does not have good fuel combustion:

1. Find the roughest speed of the engine.

2. Maintain this speed until the test is completed.

3. Loosen a fuel line nut at the fuel injection pump.

   This stops the fuel flow to that cylinder.

   Note: Take great care to tighten each fuel line after testing a cylinder and before loosening the next fuel line nut.

4. Repeat Step 3 for each cylinder until a loosened fuel line makes no difference in the engine's performance.

   This is only an indication of a problem.

This easy test can also indicate that the fuel injection pump has a problem, so the cylinder must be checked thoroughly.