The purpose of road testing is basically to confirm or deny the existence of an engine fault. Procedure is as follows:
1. Note condition of wheels/tires before test. Worn, damaged tires or wheels can cause vibration or noise.
2. Check and adjust lube levels in engine and transmission and top off engine coolant if necessary.
3. Turn off A/C system.
4. Start and run engine at idle speed with transmission in neutral. Record any noise or vibration that may be present.
“Rev” engine and note any noise/vibration plus any change in magnitude or frequency.
5. Drive vehicle at legal speed and note any evidence of noise, vibration, low power, miss, etc.
a. If vibration was noted, drive vehicle above vibration speed. Then shift into neutral and coast down through problem range. If vibration still occurs, problem is with chassis component. However, if vibration ceases, problem is with driveline component.
b. If noise is noted, shift into neutral at about 35 mph and note if noise changes in pitch, frequency, or stops altogether.
6. Operate A/C system and note effect. If noise or vibration begins, problem is related to A/C compressor, clutch, accessory mounting bracket, or belt. However, if noise/vibration is absent, note this and proceed to next step.
7. Connect compound gauge to manifold air intake tube fitting. Then press accelerator pedal to wide open position and record boost reading which should be 2 psi or greater.
