SPN 307 FMI 0Ignition/MisfireHigh
Cylinder 7 Misfire Detected
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 307 / FMI 0
Category
Ignition/Misfire
Severity
High
Regen Inhibit
No
Inducement Risk
No
Component Location: Cylinder 7 injector, fuel delivery components, and combustion chamber are located on the engine block specific to the seventh cylinder position.
Common Symptoms
- Rough idle or engine vibration at idle
- Loss of power or reduced engine performance
- Increased fuel consumption
- Black or excessive exhaust smoke
- MIL or Check Engine lamp illuminated
- Engine hesitation or stumble under load
Root Causes
- Faulty or worn injector on cylinder 7 (stuck open, poor spray pattern, or electrical failure)
- Low compression on cylinder 7 (worn rings, valve seat recession, or head gasket failure)
- Damaged or failed glow plug on cylinder 7 causing cold-start misfire
- Wiring harness damage or connector corrosion at cylinder 7 injector
- Camshaft or rocker arm wear causing insufficient valve lift on cylinder 7
Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.
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Derate Behavior
Mileage / Regen Notes
Active misfire on cylinder 7 will typically inhibit or abort active DPF regeneration due to unburned fuel risk; soot loading may accelerate requiring manual regen after repair.
System Interactions
SPN 307 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.
Common Diagnostic Mistakes
Replacing the sensor without verifying wiring continuity and supply voltage first.
Clearing codes without identifying and resolving the root cause — the fault will return.
Ignoring related active faults — cascading faults often share a root cause.
Skipping the connector inspection — corrosion and damaged pins are a leading cause of sensor faults.
Condemning the ECM before exhausting all wiring and component tests.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 307 FMI 0 — Full FSM Sequence & Repair Steps — includes wiring notes, sensor specs, and gated repair procedures.
Authority References
Diagnostic procedures on this page are informed by OEM service literature and industry standards.
Cummins QuickServe OnlineOfficial Cummins service manuals, fault code lookup, and TSB database.Detroit Diesel DiagnoCentralDetroit Diesel diagnostic procedures, DDDL documentation, and service literature.PACCAR MX Engine ServicePACCAR MX-11 and MX-13 engine service documentation and DAVIE diagnostic guides.Volvo/Mack Tech ToolVolvo and Mack engine fault code reference and PTT/Tech Tool diagnostic procedures.ASE — Diesel Truck Technician CertificationNational Institute for Automotive Service Excellence — T2 Diesel Engines certification standards.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.
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