| Possible cause of the malfunction | Method of elimination |
| Fuel supply pressure below normal | |
| Clogged fuel filter | Replace the fuel filter |
| Fuel leak through the drain circuit due to a leaky fuel pressure regulator installation | Replace the fuel pump |
| Fuel supply pressure is above normal | |
| Fuel pressure regulator sticking | Replace the fuel pump |
| Clogged or pinched drain hose or fuel line | Replace the hose or fuel line |
| After the engine stops, the fuel pressure slowly decreases | |
| Fuel leak through injectors | Replace the injectors |
| Fuel pressure drops immediately after engine stops | |
| Fuel pump check valve stuck open | Replace the fuel pump |
When troubleshooting an engine, begin by checking the operation and inspecting the major systems. If the engine is not running properly, has a rough idle, or lacks acceleration, check the following major systems:
1. Electrical power supply
- Battery
- Burn-through jumper
- Fuse box
2. Connections to ground
3. Fuel supply
- Fuel line
- Fuel filter
- Fuel pump
4. Ignition system
- Spark plug
- High voltage wires
- Ignition coil
5. Emission control system
- Crankcase ventilation system
- Vacuum leak
6. Others
- Setting the ignition timing
- Idle speed
MFI system malfunctions are often caused by poor contacts in the wiring harness connectors. Therefore, check that all connectors are securely connected.