Before performing diagnostics, check the following items which might affect engine problems:
BATTERY
1. Measure battery voltage and specific gravity of electrolyte.
Standard voltage: 12 V
Specific gravity: Above 1.260
2. Check the condition of the main and other fuses, and harnesses and connectors. Also check for proper grounding.
ENGINE GROUNDING
Make sure the engine grounding terminal is properly connected to the engine.