P0304 Code: Cylinder 4 Misfire? Complete Rohnert Park Guide

P0304 - Cylinder 4 Misfire Detected. If you're seeing this code, your engine's cylinder 4 isn't firing properly. With 8,000+ monthly searches, P0304 affects many drivers. With proper diagnosis, most repairs are affordable. As ASE-certified technicians in Rohnert Park with 25+ years of misfire diagnostics, we've fixed thousands of cylinder 4 misfires efficiently. This guide explains P0304 and your repair options.

What is P0304?

A misfire occurs when combustion fails in a cylinder. P0304 specifically means cylinder 4 (the location depends on your vehicle's design) has failed to fire one or more times. Your vehicle's computer detected this and set the code. This is your engine telling you cylinder 4 needs attention.

Symptoms of P0304

• Check engine light (solid, unless multiple misfires - then flashing)

• Rough idle with hesitation

• Power loss during acceleration

• Engine shaking or vibration

• Possible wet or fouled spark plug 4

⚠️ If light flashes: stop driving immediately - catalytic converter damage is occurring.

Common Causes of P0304 (Ranked by Probability)

1. Bad Spark Plug (35%) - Most Affordable Fix

Spark plug 4 is fouled, worn, or failed. Spark plugs deteriorate with age (typically 30,000-100,000 miles). This is the most common misfire cause.

2. Faulty Ignition Coil (40%) - Moderate Cost

Modern engines have one coil per cylinder or coil pack. If coil 4 fails, no spark in cylinder 4. Slightly more common than plugs in newer vehicles.

3. Bad Fuel Injector (15%) - Moderate Cost

Fuel injector 4 clogs or fails, preventing fuel delivery. Cylinder 4 gets spark but no fuel, causing misfire.

4. Compression Loss (10%) - Higher Investment

Damaged piston, broken valve, or blown head gasket in cylinder 4 causes compression loss. More expensive repair.

P0304 Repair Options in Rohnert Park

• **Spark Plug Replacement:** Most affordable first check

• **Ignition Coil Replacement:** Moderate cost

• **Fuel Injector Cleaning/Replacement:** Moderate cost

• **Compression Test:** Diagnostic service

• **Professional Diagnosis:** FREE at Rohnert Park Transmission

• **Call (707) 584-7727 for an accurate quote based on your vehicle**

DIY vs Professional

Spark Plug Replacement: Difficulty 3/10 - Many owners can DIY. Coil removal may be required.

Ignition Coil Replacement: Difficulty 4/10 - Straightforward but requires correct coil for your vehicle.

Fuel System Work: Difficulty 7/10 - Requires professional equipment.

Professional advantage: Diagnostic testing (compression, fuel pressure, coil resistance) confirms the exact cause before parts replacement.

Next Steps

1. **Get Professional Diagnosis** - Call (707) 584-7727 for compression test and electrical diagnostics.

2. **Start with Cheapest Fix** - Spark plug 4 is usually the answer and most affordable to replace.

3. **Schedule Service** - Most P0304 repairs complete same-day.

Conclusion

P0304 is usually an affordable repair when properly diagnosed. The key is identifying whether it's spark plug, coil, injector, or compression loss. Wrong diagnosis wastes money. Contact Rohnert Park Transmission & Auto Repair at (707) 584-7727 for expert cylinder 4 misfire diagnosis. Our ASE-certified technicians will test and fix the problem correctly. Same-day appointments often available.