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SPN 1322 FMI 31

Engine Misfire for Multiple Cylinders — Condition exists / not available.
A general 'this condition is present' flag, or the failure mode is not available. Many OEMs use it for status-type faults such as derates or inducements.

What the SPN covers: The engine computer has detected misfire on more than one cylinder, usually from uneven crankshaft speed between firing events. More on SPN 1322.

What FMI 31 usually points to: Check what the SPN itself describes; the FMI simply says the condition is active. More on FMI 31.

Severity

HIGH — limit use, diagnose now

Rough running under load can damage the engine and the DPF. Limit use until you know whether it is fuel supply, injectors or compression.

Likely causes

  1. Air in the fuel or low fuel supply pressure
  2. Worn, sticking or leaking injectors
  3. Low compression from rings or valves
  4. Contaminated fuel (water, wrong fuel)
  5. Injector wiring fault affecting a shared circuit

Checks & fixes (easiest first)

  1. Check fuel supply pressure and look for air with a clear line
  2. Read injector balance rates and run a cylinder cutout test
  3. Measure injector return flow
  4. Run a relative compression test

Troubleshooting guides

FAQ

What does SPN 1322 FMI 31 mean?

Engine Misfire for Multiple Cylinders — condition exists / not available. A general 'this condition is present' flag, or the failure mode is not available. Many OEMs use it for status-type faults such as derates or inducements.

Is SPN 1322 FMI 31 serious?

Rough running under load can damage the engine and the DPF. Limit use until you know whether it is fuel supply, injectors or compression.

What should I check first for SPN 1322 FMI 31?

Check fuel supply pressure and look for air with a clear line; Read injector balance rates and run a cylinder cutout test; Measure injector return flow.