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Cylinder 7 is on the passenger rear of most V8 layouts. It can be harder to reach and is more prone to heat-related coil failures. On Dodge HEMI engines, the Active Fuel Management system can contribute to cylinder 7 issues - check if AFM is active when the misfire occurs. See top-rated scanners on Amazon ↗
🗺️ Where Is the Problem?
Blueprint view - P0307 fault localized to cylinder #7 (spark plug, ignition coil, or fuel injector)
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0307 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
🔎 Get the ranking for my exact car - $5.99 →
🎯 Top Causes & Probability
50%
#1 - Most Likely
Bad Spark Plug (Cylinder 7)
A fouled or worn spark plug in cylinder 7 is the most common cause. On V8 engines cylinder 7 is on the rear of the passenger bank and can accumulate heat damage over time. Worn plugs with excessive gap cause incomplete combustion and trigger P0307.
🔩 Part
$5–$30
👨🔧 Labor
$0–$80
⚡ DIY Difficulty
Easy–Med
30%
#2 - Check First
Failed Ignition Coil (Cylinder 7)
The coil pack on cylinder 7 has failed or has a cracked boot allowing moisture ingress. On V8 trucks, coils on the rear cylinders are exposed to more heat from the exhaust and transmission tunnel, accelerating degradation. Swap the coil to confirm before purchasing a replacement.
🔩 Part
$20–$120
👨🔧 Labor
$30–$100
⚡ DIY Difficulty
Easy
12%
#3 - Less Common
Clogged Injector (Cylinder 7)
A partially blocked fuel injector on cylinder 7 leads to a lean misfire. Injector clogs often develop gradually and may only cause intermittent misfires at first. Running a quality fuel injector cleaner through a full tank can sometimes resolve minor deposits.
🔩 Part
$25–$150
👨🔧 Labor
$50–$100
⚡ DIY Difficulty
Medium
8%
#4 -
Low Compression (Cylinder 7)
If compression in cylinder 7 is low due to worn rings or a valve problem, the misfire will persist regardless of ignition repairs. This is the most serious possible cause and requires a compression test to confirm. Engine repair or overhaul may be necessary.
🔩 Part
$100–$2,000+
👨🔧 Labor
$500–$3,000
⚡ DIY Difficulty
Hard
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Swap Spark Plug Cylinder 7 → Cylinder 8 - Relocate the cylinder 7 plug to cylinder 8. Clear codes and drive. If P0308 now appears instead of P0307, the plug was the problem. Replace all plugs as a complete set.
- Swap Ignition Coil Cylinder 7 → Cylinder 8 - If the plug swap didn't move the code, swap the coil to cylinder 8 and retest. A code that follows the coil confirms a failed coil unit. Inspect the boot carefully for cracks before installing a replacement.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need