SPN 1322 FMI 31 is the Detroit DD Series fault-code troubleshooting sheet that documents a multiple cylinder misfire detected at idle on the Motor Control Module engine platform. This 3-page reference reproduces the fault-code identification and the factory decision tree so a technician can diagnose the concern before replacing parts.
Official document details
| Brand | Detroit |
|---|---|
| Model coverage | Detroit DD Series (EPA 2007-Current) |
| System / Group | DD Series (EPA 2007-Current) / DTCs |
| Fault code | FMI 31 under SPN 1322 (GHG14) |
| Source | Detroit fault-code literature via TruckFaultCodes.com, © 2017 |
| Pages | 3 |
| Format | |
| Language | English |
SPN 1322 FMI 31 fault description
The entry conditions are engine speed above low idle, all cylinders active with no fault reactions, and steady engine speed and torque. The procedure has the technician check for and service any additional codes first, then run the Relative Cylinder Compression Test; low compression points to a mechanical concern on that cylinder. If all cylinders are within 10%, the engine is brought to operating temperature and Idle Speed Balance values are read, with a reading at the +100 maximum limit flagging a cylinder. The technician then inspects the high pressure fuel line and, if it is undamaged, replaces the identified fuel injector.
The SPN 1322 FMI 31 sheet identifies the following likely causes and check points:
- Cylinder kit or valve train failure
- Incorrect valve lash adjustment
- Faulty fuel injector or debris entering an injector
- Damaged high pressure fuel line from rail to injector
Document table of contents
- Description and entry conditions
- Check for multiple codes
- Relative Cylinder Compression Test
- Idle Speed Balance evaluation
- High pressure fuel line and injector inspection
Applicable truck models
This troubleshooting sheet applies to Detroit DD Series engines built from EPA 2007 to current that use the Motor Control Module (MCM) and Common Powertrain Controller architecture. Confirm the engine’s emissions family and calibration against the manufacturer’s official documentation at the Detroit engine website before repairs.
Who needs this SPN 1322 FMI 31 manual
Heavy-duty diesel technicians, fleet shops and mobile mechanics who retrieve this code on a Detroit DD engine need this manual to follow the factory decision tree instead of guessing. It is written for anyone using DDDL or an equivalent diesel diagnostic tool who wants the exact test values before condemning a component.
The full 3-page PDF of this procedure is available in the DiagTechPro manuals library; a free account is required to download.
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