The largest online repair guide library for every car

About us
Contact support
FAQ
Sign up
Sign in

2018 Discovery Sport Misfire and Rough Idle - P0303 Code

0

Nicole W. · rep 0 · May 22, 6:28 AM · 1 replies · solved · Question

Vehicle: 2018 Land Rover Discovery Sport HSE

Hey everyone,

I'm having a persistent issue with my 2018 Land Rover Discovery Sport HSE. Lately, the engine has developed a really rough idle, especially when cold, and I can feel a distinct misfire while driving. The check engine light came on, and when I scanned it, I got a P0303 code, indicating a misfire on cylinder 3.

I've tried running some fuel injector cleaner, but it hasn't made any difference. The car feels sluggish, and the fuel economy seems to have taken a hit. Has anyone else experienced this with their Discovery Sport, particularly around this model year? What was the fix?

Any advice on what I should check next before taking it to the dealership would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 6:28 AM

0

ClearTheCode admin answer:

A P0303 code indicates a misfire detected in cylinder 3. This is a common issue with various potential causes. Here's a breakdown of what to check and when to seek professional help:

Common Causes & Diagnostics:

  1. Spark Plug: A faulty or worn spark plug in cylinder 3 is a very common culprit. Inspect the spark plug for cracks, excessive wear, or fouling. You can try swapping the spark plug from cylinder 3 with another cylinder (e.g., cylinder 1) and see if the misfire code follows the plug (e.g., changes to P0301). If it does, replace the plug.
  2. Ignition Coil: The ignition coil for cylinder 3 might be failing. Similar to the spark plug, you can swap the coil pack from cylinder 3 with one from another cylinder. If the misfire code changes to reflect the new cylinder, the coil pack is bad and needs replacement.
  3. Fuel Injector: A clogged or faulty fuel injector for cylinder 3 can prevent proper fuel delivery, leading to a misfire. This is harder to diagnose without specialized tools. A mechanic can test injector pulse and spray pattern.
  4. Compression Issue: Less common but more serious, low compression in cylinder 3 due to valve issues, piston rings, or head gasket problems can cause a misfire. A compression test would be necessary to confirm this.
  5. Vacuum Leaks: While less likely to cause a single-cylinder misfire, a significant vacuum leak could affect engine performance broadly.

When to See a Shop:

  • If swapping spark plugs and ignition coils doesn't resolve the issue, or if the misfire persists.
  • If you suspect a fuel injector problem, as specialized tools are often needed for diagnosis and replacement.
  • If a compression test is required, or if you suspect internal engine damage.
  • If the check engine light is flashing, this indicates a severe misfire that could damage the catalytic converter, and you should stop driving immediately and have the vehicle towed to a shop.
Menu

Help & account