P0308 Misfire detected in cylinder 8

Cylinder 8 misfire

P0308 in short

P0308 means the engine computer detected misfires in cylinder 8. The usual causes are that cylinder's ignition coil or spark plug, then its injector or low compression. Swapping the coil with another cylinder is the quickest first test. Drive gently to a shop soon; if the light flashes, stop driving.

The engine computer measures how smoothly the crankshaft speeds up after each cylinder fires. When one cylinder fails to burn its charge, the crankshaft slows for an instant at that point in the firing order and the computer counts a misfire against that cylinder.

OBD II rules require the computer to identify the cylinder when the misfire is in one cylinder, which is why you get P0308 instead of a general misfire code. Because the problem is in one place, the cause is usually something that serves only cylinder 8: its coil, plug, injector or valves.

Cylinders 7 and 8 only exist on engines with eight or more cylinders, which in practice means V8 trucks, SUVs, vans and performance cars. Which cylinder is number 8 depends on the engine, so check the service information for your engine before removing parts. If the light flashes, misfire is heavy enough to damage the catalytic converter. On V8s with cylinder deactivation (GM Active Fuel Management, Ram and Ford cylinder deactivation), lifter and valvetrain faults are a known extra cause when the usual parts check out.

Most likely causes

  1. Faulty ignition coil on cylinder 8

    Common general cause
    Why it ranks here
    On coil-on-plug engines each cylinder has its own coil, and a weak coil is one of the most common reasons a single cylinder misfires. GM's misfire procedure starts with swapping it.
    What would change this
    Rises sharply if the misfire moves to another cylinder when the coil is swapped; falls if it stays on cylinder 8.
    How to test the ignition coil

  2. Worn, damaged or fouled spark plug in cylinder 8

    Common general cause
    Why it ranks here
    A worn or fouled plug cannot fire reliably; NGK notes deposits let voltage leak away. A worn plug also overloads the coil.
    What would change this
    Rises if the plug is past its interval, has a worn electrode or shows carbon, oil or fuel fouling, or if the misfire follows the plug when swapped.
    How to test the spark plug

  3. Oil or water in the plug well, or a carbon-tracked coil boot

    Common general cause
    Why it ranks here
    Oil from a leaking valve cover gasket or water in the plug recess breaks down coil and boot insulation so the spark tracks to ground.
    What would change this
    Rises if the plug well is wet or the boot shows a carbon line; the leak must be fixed or the new coil will fail too.
    How to test the ignition coil

  4. Loose spark plug wire (GM V8s with coil-near-plug wires)

    Supported by vehicle data
    Why it ranks here
    On 2014-2019 GM V8s that use short plug wires from coil to plug, GM points to a loose wire with a missing retaining clip at the coil end as a misfire cause.
    What would change this
    Applies where the engine uses plug wires; rises if the wire on that cylinder is loose or its clip is missing.
    How to test the spark plug

  5. Clogged, leaking or disconnected fuel injector on cylinder 8

    Common general cause
    Why it ranks here
    If ignition parts check out, the injector feeding that one cylinder is the next most likely cause.
    What would change this
    A fuel-wet plug suggests a leaking injector; a dry plug with good spark suggests a restricted injector. An injector balance test or GM-style propane enrichment narrows it.
    How to test the fuel injector

  6. Low compression in cylinder 8 (valve, ring or head gasket)

    Possible — needs testing
    Why it ranks here
    Mechanical faults cause single-cylinder misfire but are less common and must be proved by testing.
    What would change this
    A compression or leakage test showing cylinder 8 low raises it; even readings rule it out.

  7. Worn camshaft lobe, lifter or valve on that cylinder (some V8s)

    Supported by vehicle data
    Why it ranks here
    GM tells technicians to check for a worn cam lobe or lifter roller, a sticking or leaking valve, a broken valve spring or a collapsed Active Fuel Management lifter when its normal misfire tests do not find the cause; GM and Ford have later bulletins for lifters that came apart and for camshaft or tappet wear with a ticking noise.
    What would change this
    Rises with a ticking or tapping noise from that cylinder, a cylinder that misfires with good spark and fuel, or low compression or leakage on that cylinder.

  8. Damaged wiring or loose connector at cylinder 8's coil or injector

    Possible — needs testing
    Why it ranks here
    Weak supply voltage or poor connections can stop one coil or injector working, but this is less common than the parts themselves.
    What would change this
    Rises if the misfire changes when the harness is moved or the connector is corroded or loose.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all codes and freeze-frame data, and find where cylinder 8 is on your engine in the service information.

    Low riskTool: scan tool, service information

    • IfOnly P0308 is stored (or P0308 plus P0300)

      It meansFocus on cylinder 8.

      Go to step 2

    • IfLean codes P0171/P0174 or misfire codes for several cylinders are also stored

      It meansA shared cause may be involved; follow the P0300 tests as well.

  2. With the engine off and cool, remove cylinder 8's coil and look for cracks, carbon tracks, and oil or water in the plug well.

    Use cautionTool: basic hand tools, inspection light

    Warning:Work only with the engine off and cool; plugs and exhaust parts can burn. Never handle coils, boots or plug wires with the engine running; ignition voltage can shock you.

  3. Swap cylinder 8's coil with the coil from a neighbouring cylinder, clear the codes and drive until the misfire monitor runs again.

    Use cautionTool: scan tool, basic hand tools

    Warning:Engine off and key out when swapping coils. Do not unplug coils on a running engine to find the bad cylinder; it risks a shock and can damage a weak coil.

  4. Remove cylinder 8's spark plug and inspect it; if it looks normal, swap it with another cylinder's plug and retest.

    Use cautionTool: spark plug socket

    Warning:Engine cold only. Thread plugs in by hand first to avoid cross-threading the cylinder head.

  5. Check cylinder 8's injector connector, then have an injector balance test (or the manufacturer's injector test) done.

    Best left to a shopTool: scan tool with injector tests, noid light

    Warning:Injector testing involves a pressurised fuel system; fuel sprays and ignites easily. Leave pressure tests to a shop.

  6. Run a compression test, then a cylinder leakage test if cylinder 8 reads low.

    Use cautionTool: compression gauge, leak-down tester

    Warning:Disable fuel and ignition as the service information describes before cranking, keep clear of belts and the fan, and let a hot engine cool first. If unsure, have a shop do it.

Symptoms

  • Rough idle or a steady shake
  • Stumble or hesitation when accelerating
  • Loss of power
  • Ticking or tapping from the top of the engine
  • Check engine light flashing Gets more serious: stop and have it checked.

Compare with: Car shaking with the check engine light on, Rough idle with the check engine light on, Check engine light with loss of power

How to fix

  1. Record the codes and freeze-frame data before clearing them.

  2. Drive gently until it is fixed: no hard acceleration, high speed or towing.

  3. If the swap test proved the coil faulty, replace it, clear the codes and confirm the misfire count stays at zero after a drive.

    Warning:Engine off and key out before unplugging the coil.

  4. If the plug is worn or due by the maintenance schedule, replace it (ideally all plugs) with the type and gap listed for your engine.

    Warning:Cold engine only; start plugs by hand to avoid cross-threading.

  5. If oil was in the plug well, have the valve cover or tube seal leak fixed too, or the new coil will fail.

On your vehicle

Chevrolet

  • 2002–2022 · Silverado 1500

    Supported by vehicle data

    GM V8 trucks have several bulletins for cylinder misfire codes including P0308: a loose plug wire with a missing clip (2014-2019), worn or collapsed Active Fuel Management lifters and other valvetrain wear (2002-2018), and lifters that came apart (2022). If coils and plugs check out, ask the shop about these.

  • 2002–2022 · Tahoe

    Supported by vehicle data

    Covered by the same GM V8 misfire bulletins as the Silverado: loose plug wire (2015-2019), valvetrain and AFM lifter checks (2002-2018) and failed lifters (2022).

  • PIP4138RStatus unverified

    GM PIP4138R: P0300-P0308 not isolated by service information, check valvetrain

    2002–2018silverado-1500, tahoe, suburban, express, camaro, corvette · issued · NHTSA 10147382

    When published diagnostics do not find the cause of misfire codes P0300-P0308 (with or without engine noise), GM tells technicians to check for a worn camshaft lobe or lifter roller, a sticking or leaking valve, a broken valve spring and a collapsed Active Fuel Management lifter. Also lists GMC, Cadillac, Buick and Pontiac V8 models.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PIP5159CStatus unverified

    GM PIP5159C: P0300-P0308 from a loose spark plug wire

    2014–2019silverado-1500, tahoe, suburban, camaro, corvette · issued · NHTSA 10149051

    Inspect for a loose spark plug wire; if one is loose, check for a missing C clip at the coil end and replace the wire if the clip is missing. Also lists GMC Sierra and Yukon and Cadillac Escalade and CTS-V.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • PIP5861Status unverified

    GM PIP5861: misfire P0300-P0308 from a lifter that has come apart

    2022silverado-1500, tahoe, suburban · issued · NHTSA 10217780

    Diagnosis of misfire codes may find a lifter has come apart; GM recommends replacing the lifter guide and the four lifters. Also lists GMC Sierra 1500 and Yukon and Cadillac Escalade.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Ford

  • 2020–2025 · F-250 Super Duty

    Supported by vehicle data

    On gas Super Duty engines, Ford links an upper-engine tick with misfire codes P0301-P0308 to camshaft or tappet wear. Ask a dealer to check TSB 25-2572.

  • 2021–2025 · E-Series

    Supported by vehicle data

    On gas E-Series vans, Ford links an upper-engine tick with misfire codes P0301-P0308 to camshaft or tappet wear (TSB 25-2572).

  • 2024 · Mustang

    Supported by vehicle data

    On the Dark Horse with a manual transmission, Ford says P0300, P0302 and P0308 can set after repeated runs to maximum engine speed on a track (SSM 52926). Mention any track use to the dealer.

  • TSB 25-2572Status unverified

    Ford TSB 25-2572: upper engine tick and misfire P0301-P0308 from camshaft or tappet wear

    2020–2025f-250-super-duty, e-series · issued · NHTSA 11025854

    Some gas Super Duty, E-Series, F-53 and F-650/F-750 may have an upper-engine tick at idle, rough running, misfire or a MIL with P0301-P0308, possibly from camshaft and/or valve tappet wear. Supersedes TSB 25-2322.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • SSM 52926Status unverified

    Ford SSM 52926: P0300, P0302 and P0308 after racetrack use

    2024mustang · issued · NHTSA 11007978

    2024 Mustang Dark Horse with a manual transmission may set P0300, P0302 and P0308 after extended high-speed or racetrack driving that repeatedly hits maximum engine speed.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • P0307Misfire detected in cylinder 7

    Same system Common general cause

    P0307 is the same misfire count on cylinder 7. Both together, or with other cylinder codes on a V8, point to a shared cause such as fuel, software or valvetrain rather than one coil.

  • P0300Random or multiple-cylinder misfire detected

    Same system Common general cause

    P0300 is stored when misfire spreads to more than one cylinder. If P0308 appears with P0300, cylinder 8 is usually the worst; if other cylinder codes appear too, look for a shared cause.

  • P0420Catalytic converter efficiency below the computer's limit (Bank 1)

    Primary / secondary Common general cause

    Likely primary: P0308. A cylinder that keeps misfiring sends unburned fuel into the catalytic converter, which can overheat and fail, later setting P0420. Fix the misfire before replacing the converter.

  • P0171Engine computer has reached its limit adding fuel on bank 1: the mixture is lean

    Primary / secondary Common general cause

    Likely primary: P0171. If P0171 is stored too, a lean bank 1 may be the shared cause: a lean mixture can make cylinders misfire. Fix the lean condition first and follow the P0300 tests as well.

  • P0174Engine computer has reached its limit adding fuel on bank 2: the mixture is lean

    Primary / secondary Common general cause

    Likely primary: P0174. If P0174 is stored too, a lean bank 2 may be the shared cause: a lean mixture can make cylinders misfire. Fix the lean condition first and follow the P0300 tests as well.

All Misfire codes

P0308 questions

Can I drive with a flashing check engine light?

Not if you can avoid it. A flashing light means misfire severe enough to overheat the catalytic converter is happening now. Ford's owner guide warns the heat can damage the converter and could start a fire; EPA advises keeping driving to a minimum. Drive gently to the nearest shop at most, or have it towed.

How do I tell a bad coil from a bad spark plug?

Swap them. Move the coil from the misfiring cylinder to a neighbouring cylinder, clear the code and drive. If the misfire moves with the coil, the coil is bad. If it stays put, swap the spark plug the same way. If it still stays, look at the injector and compression.

Which cylinder is number 1, 2, 3 and so on?

It depends on the engine. Manufacturers number cylinders differently, especially on V6 and V8 engines where the banks may be numbered side by side or alternately. Check the service information or a repair manual for your exact engine before you pull a coil or plug.

Sources and review

  1. Cal. Code Regs. tit. 13, § 1968.2 - Malfunction and Diagnostic System Requirements (OBD II) — California Air Resources Board (via Cornell LII)
  2. 2001 Lincoln Continental Owner's Guide - Warning lights (Check engine) — Ford Motor Company
  3. Do you drive a 1996 or newer car or light truck? (On-Board Diagnostics, EPA420-F-02-016) — U.S. Environmental Protection Agency
  4. Causes of ignition coil failure — DENSO Aftermarket Europe ,
  5. How To Diagnose & Repair Engine Misfires — AA1Car.com (Larry Carley, automotive technical writer)
  6. GM PIP5062C: P0300 with a misfiring cylinder making little or no power — General Motors (via NHTSA) ,
  7. Technical Information: Fouling of Spark Plugs — NGK Spark Plugs (Niterra UK)
  8. GM PIP5159C: P0300-P0308, loose spark plug wire with a missing C clip, 2014-2019 GM V8 — General Motors / NHTSA ,
  9. GM PIP4138R: misfire codes P0300-P0308 that service information does not isolate, check valvetrain and AFM lifters — General Motors / NHTSA ,
  10. GM PIP5861: misfire P0300-P0308 from a lifter that has come apart, 2022 GM full-size trucks and SUVs — General Motors / NHTSA ,
  11. Ford TSB 25-2572: upper engine tick, misfire and P0301-P0308 from camshaft or tappet wear, 2020-2025 gas Super Duty and E-Series — Ford Motor Company / NHTSA ,
  12. Ignition system troubleshooting tips to maximise lifetime — DENSO Aftermarket Europe ,
  13. ASE L1 study guide: Misfire codes — OpenExamPrep (independent study site, not affiliated with ASE)
  14. What You Should Know About Catalytic Converters — AA1Car.com (Larry Carley, automotive technical writer)
  15. Ford SSM 52926: P0300, P0302 and P0308 after track use, 2024 Mustang Dark Horse manual — Ford Motor Company / NHTSA ,
Last reviewed
Written by
Saurabh K.
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