- Check fuel quality
- Poor fuel quality, low cetane rating, additives, improper mixing with kerosene or gasoline can cause a less combustible mixture and possible misfire.
- Check fuel supply system for air leaks
- Loose connections or cracked hoses between the fuel tank and injection pump may result in air in the fuel system. Air trapped in injectors or lines can cause a misfire or knocking noise.
- Check fuel delivery system for fuel leaks
- Fuel leaks at fuel lines and fuel delivery valves reduce fuel pressure and therefore affect fuel delivery to the cylinders.
- Check injection pump mounting brackets
- Loose pump mounting brackets can cause pump misalignment and injection timing change resulting in a misfire or knocking noise.
- Idle speed drop test
- Whether or not fuel is being supplied to injectors can be verified so that a misfire or knocking noise can be isolated to the affected cylinder
- Test Injectors
- Check valve clearance
- Check compression
Quality check:
- Start engine, allow to warm up and observe idle quality
- engine should idle smoothly
- engine should not misfire or knock
- With correct tire pressure, drive car on a level road
- Accelerate to a constant speed of 35 MPH
- in 3rd gear (4-speed transmission)
- in 4th gear (5-speed transmission)
- Accelerate again to full throttle and note the acceleration quality.
- engine should accelerate evenly
- engine should not misfire or knock
- Maintain steady speed and observe performance quality
- engine should maintain even performance at all speeds and show no symptoms of misfire or knock
If test passed, return car to customer
If test failed, perform diagnosis III