What are the symptoms of SPN 1325 FMI 13?

Rough idle or engine vibration. Reduced power and acceleration. Increased fuel consumption. White or black smoke from exhaust. Engine misfire detected on cylinder 3. Check engine light illuminated

What causes SPN 1325 FMI 13?

Faulty or worn fuel injector on cylinder 3 causing incorrect fuel delivery. Low compression on cylinder 3 due to worn rings, valves, or head gasket failure. Injector return line restriction or excessive back pressure on cylinder 3. Injector driver circuit fault or ECM injector output degradation for cylinder 3. Air in fuel system affecting cylinder 3 injector performance. Incorrect injector trim/calibration code not programmed after injector replacement. Camshaft or crankshaft timing issue affecting cylinder 3 firing event. Wiring harness damage or chafing on cylinder 3 injector circuit. Failed or sticking cylinder 3 injector solenoid or piezo element. High-pressure fuel system pressure deviation affecting cylinder 3

How do I diagnose SPN 1325 FMI 13?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 1325 FMI 13 are available inside the AI Diesel Tech guided diagnostic session. The AI walks you through every test — one step at a time.

SPN 1325 FMI 13Engine Protection

Misfire Cylinder 3 - Out of Calibration

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Overview

Fault Code

SPN 1325 / FMI 13

Common Symptoms

Rough idle or engine vibration
Reduced power and acceleration
Increased fuel consumption
White or black smoke from exhaust
Engine misfire detected on cylinder 3
Check engine light illuminated

Root Causes

Faulty or worn fuel injector on cylinder 3 causing incorrect fuel delivery
Low compression on cylinder 3 due to worn rings, valves, or head gasket failure
Injector return line restriction or excessive back pressure on cylinder 3
Injector driver circuit fault or ECM injector output degradation for cylinder 3
Air in fuel system affecting cylinder 3 injector performance
Incorrect injector trim/calibration code not programmed after injector replacement
Camshaft or crankshaft timing issue affecting cylinder 3 firing event
Wiring harness damage or chafing on cylinder 3 injector circuit
Failed or sticking cylinder 3 injector solenoid or piezo element
High-pressure fuel system pressure deviation affecting cylinder 3

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

Power Derate

Yes

Mileage / Regen Notes

Active and parked DPF regeneration may be inhibited or suspended when a misfire fault is active on cylinder 3, as unburned fuel entering the aftertreatment system poses a risk of DPF damage or uncontrolled exotherm. Engine protection derate may also prevent regen conditions from being met.

System Interactions

SPN 1325 FMI 13 interacts with the following systems and may trigger cascading faults if not resolved promptly.

ECM communication — J1939 network faults can affect all connected modules

Engine protection — ECM may trigger derate to prevent damage

Aftertreatment — engine protection derates can affect regen strategy

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

SPN 1569-31Engine Protection Derate SPN 100-1Oil Pressure Low SPN 190-0Engine Speed High SPN 111-4Coolant Level Sensor Low

OEM System Resources

Cummins Fault Codes Detroit Diesel Fault Codes PACCAR Fault Codes Volvo Fault Codes Freightliner Fault Codes Mack Fault Codes

ASE Training Resources

Why ASE Certification Matters How ASE Tests Work ASE Study Tips ASE vs AI Diesel Tech Certification Paths Get Started with ASE

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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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