Diesel Trouble Codes

Rough Idle or Misfire — 6.4 Power Stroke

A rough idle or misfire on the 2008–2010 6.4L Power Stroke usually points to an injector — weak, leaking or with a circuit fault — or, when it is worst cold…

Updated October 15, 2026

What’s going on

On the 6.4L Power Stroke a rough idle or misfire typically indicates uneven cylinder contribution from fuel delivery or cold-start aid issues. The platform uses common-rail piezo injectors driven by the PCM’s injector driver circuits and glow plugs for cold start. A rough idle or misfire on the 6.4L usually points to an injector — weak, leaking or with a circuit fault — or, when it is worst cold, glow plug problems. Contribution/balance codes are in the P0263/P0266/P0269 family and injector circuit faults are P0201–P0208.123

Most likely causes

  1. Weak or leaking injector causing cylinder contribution/balance fault — A failing piezo injector can deliver incorrect quantity or leak, producing a rough idle and misfire. Late post-injection during regen can wash fuel past the rings, contributing to engine-oil fuel dilution. This condition commonly sets P0263 on cylinder 1 and the Pxx6x family for other cylinders.142
  2. Injector driver circuit fault — Open or high-resistance in the PCM-driven injector circuit for a cylinder causes a misfire and rough idle. On this platform the 6.4 has no separate valve-cover FICM; injectors are driven by injector driver circuits in the PCM. This commonly sets P0201 for cylinder 1 and the P020x family for other cylinders.13
  3. Glow plug or glow plug control module degradation — Weak glow plugs or a failing control module make cold starts and cold idle rough. The 6.4 uses eight glow plugs with a control module, not a grid heater. Cold-start misfire that improves as the engine warms points here. Related trouble code on this platform is P0683.15
  4. High-pressure fuel leak affecting rail pressure control — A leaking injector, weeping high-pressure line/fitting, worn high-pressure pump, or rail-pressure relief valve can cause rail pressure the PCM cannot maintain, leading to rough idle and misfire. The 6.4 is common rail with a gear-driven high-pressure pump and rail pressure sensor; the PCM regulates pressure with a fuel pressure control/volume control valve on the pump. Fuel system leak codes P0093/P0094 are a signature 6.4 issue.56

How to narrow it down

  1. Read stored trouble codes and freeze frame; note any P0263 contribution/balance, P0201 injector circuit, or P0683 glow plug control module codes.
  2. Check engine oil level and smell for fuel; rising level or thin, fuel-smelling oil suggests fuel dilution from leaking injectors or excessive regen post-injection.
  3. Perform a cold-start test; observe if roughness is worst cold and improves with engine temperature, indicating glow plug or control module performance.
  4. Inspect injector electrical connections and harness for chafing, corrosion, or oil intrusion at the valve cover pass-throughs; verify injector driver circuit integrity for the affected cylinder.
  5. Monitor rail pressure at idle with a scan tool; compare actual vs desired pressure and look for pressure drops that suggest a high-pressure leak or pump control issue.
  6. Run a cylinder contribution/balance test using the scan tool to identify the weak cylinder; correlate with P0263/P026x codes.
  7. If a specific cylinder is identified, perform an injector buzz test and electrical resistance check per service information to confirm injector circuit health before condemning the injector.

Specs and test values

CheckNormal readingWhen to measureSource
Battery and charging voltage12.6–12.7 V at rest when fully charged; about 13.5 V runningEngine off, then running with loads onDieselHub
Glow plug resistanceLow — usually no more than about 6 Ω — and similar on every plug; an open reading means a failed plugEngine off, meter lead to engine groundDENSO

Common mistake to avoid

Replacing glow plugs or the glow module before checking the batteries. The glow system draws heavily, and low battery voltage causes circuit faults that no part swap will fix. Source: FleetRabbit — P0670 glow plug control module fault.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
Fuel supply or return line repair$30–$2000.5–2 hrsDIY with tools and a manual
Glow plugs (full set)$80–$2502–6 hrsDIY with tools and a manual
Fuel injector (each)$250–$4503–5 hrsShop

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If rail pressure is unstable, high-pressure fuel leaks are suspected, or injector replacement is required, have a qualified diesel technician perform the work. High-pressure fuel systems can cause injury if mishandled. If the vehicle shows sudden power loss while driving, stop driving and tow it for inspection.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources

  1. Curated symptom seed — 6.4 Power Stroke (curated) ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — 6.4 Power Stroke (curated) ↩︎ ↩︎

  3. Curated DTC seed — 6.4 Power Stroke (curated) ↩︎ ↩︎

  4. Curated symptom seed — 6.4 Power Stroke (curated) ↩︎

  5. Curated symptom seed — 6.4 Power Stroke (curated) ↩︎ ↩︎

  6. Curated DTC seed — 6.4 Power Stroke (curated) ↩︎