3.1 Basic Troubleshooting Principles

As with any troubleshooting, analysis of the observed symptoms is the key to isolating and identifying engine problems. Begin with careful observation, keeping in mind the following questions:

How has the symptom developed? A symptom which develops quickly is probably caused by a problem which can be corrected by simple maintenance or repair. A symptom which has developed gradually over time, especially after fifty or sixty thousand miles, is more likely an indication of general wear and the need for more comprehensive overhaul work.

Is the symptom rpm-dependent? A noise which is caused by an engine mechanical problem will be dependent mainly on engine speed, with similar symptoms regardless of changes in vehicle speed. Noises which repeatedly occur only in a certain rpm range suggest a vibration problem. Noises which change with vehicle speed are more likely due to drivetrain or running gear problems.

Is the symptom load dependent? Forces at work inside a running engine vary as the demand for power varies. Symptoms which are more severe during hard acceleration indicate certain kinds of problems. Symptoms which are more apparent at no load or high vacuum (example: coasting at high rpm) point to other problems. Note that higher engine loads also affect the fuel and ignition systems, which may be responsible for high-load performance problems.

Is the symptom temperature dependent? Does it only occur when the engine is cold? Does it change as the engine warms up? How? Metal parts expand and contract with changes in temperature. Clearances change. Oil viscosity and cooling system pressure change. In troubleshooting symptoms which change as the engine gets warm, look for an engine characteristic that changes with temperature.

Table b lists symptoms of engine problems, their probable causes, and suggested corrective actions. The boldface numbers in the corrective action column indicate the heading in this section of the manual where the applicable test and repair procedures can be found.

Table b lists symptoms of engine problems, their probable causes, and suggested corrective actions. The boldface numbers in the corrective action column indicate the heading in this section of the manual where the applicable test and repair procedures can be found.

Table b. Engine Troubleshooting