Applicable Systems
3CX Backhoe
Symptoms
Engine starts but runs unevenly; misfire felt at exhaust manifold.
Possible Causes
- Injector nozzle worn causing poor atomization.
- Low compression on one cylinder due to valve seat erosion.
- High-pressure fuel line cracked introducing air.
Troubleshooting Steps
- Step 1: Perform cylinder cut-out test and observe RPM drop per cylinder.
All cylinders drop 80–120 RPM; no weak cylinder identified. - Step 2: Measure compression pressure with adapter in glow plug hole.
Compression ≥ 3.5 MPa; variation < 10% across cylinders. - Step 3: Inspect fuel lines for wetness or cracks at injector nut.
Lines dry; no visible cracking or chafing.
How to Reset
Replace faulty injector; reseat valves or replace cylinder head; replace cracked fuel line.
Common Replacement Parts
- Injector 320/06836: Injector 320/06836
- Cylinder Head Assembly 320/03574: Cylinder Head Assembly 320/03574
Frequently Asked Questions
- Q: Can one bad injector damage others?
Indirectly—uneven running stresses mounts and coupling.
- Q: What is normal compression for JCB diesel?
3.2–4.0 MPa depending on engine variant and wear.
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Source: JCB 3CX Engine Service Manual
Category: Heavy Equipment
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