Fix P0308: Mechanic’s solutions that WORKED

The P0308 is one of several misfire codes you can read on your scan tool. I studied 120+ different vehicles with misfires and how were they fixed, to provide you with a list of the most common causes, also with an action plan to diagnose this fault in no time.

You don’t want to delay fixing your P0308 as the misfire will damage your catalytic converters or engine internals. Both of these fixes are priced at thousands of dollars while the misfire is often caused by a worn-out $5 spark plug. Fix it ASAP.

P0308 quick overview

Meaning	P0308: Cylinder #8 Misfire Detected
Is it serious?	Yes, this code is serious and should be addressed immediately to prevent damage to the engine or catalytic converter.
Possible causes	-Worn or faulty spark plug in cylinder #8 -Defective ignition coil for cylinder #8 -Malfunctioning fuel injector for cylinder #8 -Mechanical engine issues (e.g., valve problems or piston ring wear) -Wiring or electrical issues related to cylinder #8
How to diagnose?	Inspect Spark Plug: Check the spark plug in cylinder #8 for signs of wear, fouling, or damage. Test Ignition Coil: Swap the ignition coil with another cylinder to see if the misfire follows. Check Fuel Injector: Perform a swap or test of the fuel injector in cylinder #8 to ensure it’s working properly. Perform Compression Test: Conduct a compression test on cylinder #8 to rule out internal mechanical issues. Inspect Wiring: Examine wiring and connectors related to cylinder #8 for any signs of damage or loose connections.

Case study: real cases of solving P0308

Check the real examples of how the P0308 was solved on different vehicles.

How to fix P0308 on Dodge

Car: 1996 Dodge Ram 1500 5.9L
Problem: P0300, P0301, P0302, P0308

Diagnosing: The technician replaced the ignition cables and fuel pump without any improvement, but the fault was indeed hiding in the fuel system. Just not the fuel pump.
Fix: Cleaning fuel injectors fixed it.

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How to fix P0308 on Lincoln

Car: 2006 Lincoln Navigator Ultimate 5.4L
Problem: Poor Idle Quality, Hesitation, Misfire, MIL Lamp on, P0308, P0316

Diagnosing: The technician replaced the ignition coil and spark plug on the #8 cylinder without success. Later testing uncovered the fault is hiding in the intake valve.
Fix: Fix engine valves.

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How to fix P0308 on another dodge

Car: 1997 Dodge Ram 1500 Laramie 5.2L
Problem: Misfire, P0300 – P0304, P0308

Diagnosing: The technician replaced basic parts like the fuel filter and spark plugs seemingly fixing the problem at first, but the car was back soon with the same codes. He discovered dropping fuel pressure at the test drive with a hooked pressure gauge. Changed the fuel pump, which seemed to fix it but the customer was back again.
Fix: Turned out some fuel injectors were clogged, cleaning them was a final fix.

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How to fix P0308 on ford

Car: 1997 Ford F-150 Lariat 4.6L
Problem: Excessive Emissions, Misfire, MIL Lamp on, P0301, P0308

Diagnosing: The technician replaced spark plugs, spark plug wires, and fuel injectors without improvement. Finally, the bad ignition coil was discovered with further testing.
Fix: Replace the ignition coil

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How to fix P0308 on Toyota

Car: 2001 Toyota Land Cruiser 4.7L
Problem: Misfire, Check engine light, P0300, P0301, P0308

Diagnosing: Recently, a customer brought in a truck experiencing misfires. Initially, three trouble codes (P0300, P0302, P0308) were found, but during a road test, additional codes (P0306, P0307) appeared. The misfire seemed to shift between cylinders, and after replacing an injector, the issue persisted with codes P0300, P0301, and P0308. All plugs were verified, and potential intake leaks and faulty MAF sensors were ruled out.
Fix: Replacement of all fuel injectors fixed the problem.

The key takeaways from these cases

• Negative fuel trims mean it is trying to correct for a rich condition. Maybe the coolant temperature sensor is sending false info to the PCM. May also be a bad map sensor.
• Remember that new aftermarket (even OEM) parts can come faulty. Don’t forget that in your diagnosing process

P0308 FAQ and conclusion:

Check the Wikipedia article on combustion engines if you are still unsure what exactly the misfire is. Understanding it will help you with your diagnosis.