Ignition

P03E4 — Cylinder 8 Combustion Problem / Misfire Detected

Severity: medium Drive with care, to a shop

What P03E4 means

The engine control module monitors crankshaft speed and noticed that cylinder 8 is not burning its air-fuel mixture properly. Good combustion needs a strong spark, the right amount of fuel and adequate compression. If any of these is missing, the cylinder misfires and P03E4 is stored.

Symptoms

  • Rough idle
  • Hesitation or stumbling under acceleration
  • Loss of power
  • Worse fuel economy
  • Check engine light on or flashing
  • Smell of unburned fuel from the exhaust

Possible causes

  1. Worn spark plug in cylinder 8
  2. Failed ignition coil or bad coil connector on cylinder 8
  3. Clogged or failing fuel injector on cylinder 8
  4. Vacuum or intake leak near cylinder 8
  5. Low compression from worn rings or a burnt or leaking valve
  6. Damaged wiring or poor connection to the coil or injector

How to diagnose

  1. Scan all codes and review freeze frame data; look for other misfire or fuel system codes
  2. Inspect the cylinder 8 plug, coil, connectors and wiring
  3. Swap the cylinder 8 coil with a neighboring one and see if the misfire follows
  4. Remove the plug, check its condition and gap, and replace the set if worn
  5. Test the injector: coil resistance, driver signal, and operation by sound or flow
  6. Check the intake manifold and vacuum hoses for leaks, using a smoke test if needed
  7. Run a compression test and, if low, a cylinder leak-down test
  8. Review fuel trims and fuel quality

Common fixes

  • Replace spark plugs, ideally the full set
  • Replace the cylinder 8 ignition coil
  • Clean or replace the cylinder 8 fuel injector
  • Fix vacuum leaks and replace damaged hoses or gaskets
  • Repair the engine mechanically: rings, valves or cylinder head

Questions and answers

What does P03E4 mean?

It means the engine computer detected a combustion problem, or misfire, in cylinder 8. The usual culprits are the spark plug, coil or injector for that cylinder.

Can I drive with P03E4?

Only for a short distance and gently if the check engine light is steady. If it flashes, do not drive, since the catalytic converter and engine can be damaged.

How do I find the cause of the cylinder 8 misfire quickly?

Swap the ignition coil (and plug) with another cylinder and see whether the code follows. If it does not, check the injector and cylinder compression.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.