Code
P1300
INFINITI
P — Powertrain
Random Misfire
AI status
Completed
Completed
100%
Causes
- Faulty spark plugs (worn, fouled, incorrect gap)
- Failing ignition coils or coil-on-plug boots
- Fuel injector failure or poor injector electrical connection
- Low fuel pressure or weak fuel pump
- Vacuum leaks or intake gasket leaks
- Low or uneven cylinder compression (mechanical problems)
Symptoms
- Rough idle and vibration
- Intermittent or constant engine stumble under load or acceleration
- Reduced engine power and drivability
- Illuminated Check Engine Light / MIL
- Decreased fuel economy and increased exhaust emissions
- Possible backfiring, hesitation, or surging
What to check
- Read and record freeze frame data and all stored DTCs with a scan tool
- Monitor live data: misfire counters per cylinder, RPM, fuel trims, O2 sensor, MAF/MAP
- Perform a visual inspection of spark plugs, coils, ignition wiring and connectors
- Check fuel pressure at the rail with a gauge under key-on and during cranking/idle/load
- Perform a smoke test to identify vacuum or intake leaks
- Measure cylinder compression or perform a leak-down test across all cylinders
Signal parameters
- Misfire counters: PCM records increased counts that are not isolated to a single cylinder
- Short-term/long-term fuel trim excursions (e.g., trims moving toward ±10% or more)
- O2 sensor switching irregularities or stuck readings indicating rich/lean conditions
- MAF mass airflow or MAP readings inconsistent with commanded load
- Fuel rail pressure: low or fluctuating compared to manufacturer specification
- Crankshaft position sensor/Camshaft position sensor signal dropout or jitter
Diagnostic algorithm
- Retrieve all codes and freeze-frame; clear codes and attempt to reproduce the fault while monitoring live misfire counters and related parameters.
- Inspect spark plugs for wear/fouling and correct gap; replace if necessary. Inspect coil boots and connectors; perform resistance/test coils under load or swap coils between cylinders to see if misfire follows the coil.
- Check injector resistance and operation with a noid light or oscilloscope; swap injectors between cylinders to isolate an injector fault.
- Measure fuel rail pressure and volume under load; inspect fuel filter and pump operation. Repair or replace failing fuel system components.
- Perform a smoke test and visual inspection for vacuum/intake manifold leaks and repair as needed.
- Check cam/crank sensor signals with a scope for missing or erratic pulses and verify valve/timing alignment; if timing is off, inspect timing chain/belt and related components.
- Perform cylinder compression test or leak-down test to identify mechanical failures (worn rings, valves, head gasket). Repair engine mechanical issues as required.
- Inspect exhaust system for downstream restriction (catalytic converter) and measure backpressure if suspected.
- Inspect wiring harnesses, grounds, and PCM connectors for corrosion, damage, or poor connections; repair and re-test.
- After repairs, clear codes and perform a road/drive cycle to confirm repair and that misfire counters remain stable with no recurrence of P1300.
Likely causes
- One or more ignition coils failing under load (intermittent misfire)
- Multiple injectors fouled or poor fuel delivery causing random misfires
- Vacuum leak or intake manifold gasket leak causing lean misfires
- Low or fluctuating fuel rail pressure under load
- Intermittent crank/cam sensor fault or timing variation
- Degraded spark plugs across several cylinders
Fault status
Status
Random/multiple cylinder misfire detected. MIL illuminated. Engine may run rough, lack power, and increase emissions. Investigate ignition, fuel, vacuum, mechanical compression, sensor signals and wiring.
Repair difficulty: Medium
Diagnostic time: 1–4 hours
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