P0308 on 2000-2006 Toyota Tundra 4.7L V8: Cylinder 8 Misfire Causes and Fixes

What's Unique About the 2000-2006 Toyota Tundra

The 4.7L 2UZ-FE V8 is a famously reliable engine, often called a 'million-mile motor'. However, as these first-generation Tundras age, the original coil-on-plug ignition coils are a common failure item after 15+ years and over 150,000 miles. The good news is that the problem is almost always isolated to a single bad coil, which is a straightforward and relatively inexpensive part to replace. Cylinder 8 is the rearmost cylinder on the passenger's side (Bank 2), which can be slightly tight to access but is manageable for most DIY mechanics.

Symptoms You May Notice

• Rough or shaky idle
• Hesitation or stumbling during acceleration
• Noticeable loss of engine power
• Flashing Check Engine Light (indicates a severe misfire that can damage the catalytic converter)
• Solid Check Engine Light
• Decreased fuel economy
• A smell of gasoline from the exhaust
• Engine may be hard to start

Most Likely Causes

1. Failed Ignition Coil 🔴 High Probability The original Denso coils from this era are known to fail after 15-20 years of heat cycles and vibration. It is the most common cause for a single-cylinder misfire on the 2UZ-FE engine.
   How to confirm: Swap the ignition coil from cylinder 8 (rear passenger side) with cylinder 6 (the next one forward on the same bank). Clear the codes and drive. If the code changes to P0306, the coil is faulty. This is the universally recommended first diagnostic step. 🎬 Watch: A quick way to identify a bad ignition coil.
   Typical fix: Replace the failed ignition coil with a new Denso or NGK part. Many owners choose to replace all eight coils and spark plugs at the same time for preventative maintenance, especially on high-mileage (150k+) vehicles, but it is not strictly necessary.
   Est. part cost: $60 - $90 for one OEM-quality coil
2. Worn or Fouled Spark Plug 🟡 Medium Probability Spark plugs are a regular maintenance item with a typical service life of 30,000 miles for standard plugs or up to 120,000 miles for iridium plugs. An excessively worn electrode increases the gap, requiring more voltage from the coil and potentially causing a weak or inconsistent spark. Oil from a leaking valve cover gasket tube seal can also foul the plug.
   How to confirm: After confirming the coil is good, move the spark plug from cylinder 8 to another cylinder (e.g., cylinder 6). If the misfire code follows the plug (P0306), the plug is the issue. Visually inspect the plug for heavy carbon buildup, oil fouling, or a worn-out electrode.
   Typical fix: Replace the spark plug. It is best practice to replace all eight spark plugs as a set 🎬 Watch: Step-by-step guide to replacing your Tundra's spark plugs. to ensure even performance. Use the correct OEM-spec Iridium plugs (Denso SK20R11 or NGK IFR6T11).
   Est. part cost: $20 - $80 for a set of 8 plugs
3. Faulty Fuel Injector ⚪ Low Probability While Denso fuel injectors are very reliable, they can become clogged or fail electrically over many years and miles, preventing the correct amount of fuel from reaching cylinder 8. This is less common than ignition issues but is the next logical item to check.
   How to confirm: Listen to the injector with a mechanic's stethoscope; it should have a consistent, rhythmic clicking sound. You can also test the injector's resistance with a multimeter. Swapping the injector with another cylinder is possible but is much more labor-intensive than swapping a coil or plug.
   Typical fix: Replace the faulty fuel injector. It's recommended to replace the O-rings and seals anytime an injector is removed.
   Est. part cost: $70 - $150 for one injector

Rare But Worth Checking

• Vacuum Leak: A leak in the intake manifold gasket near the runner for cylinder 8 can lean out the air/fuel mixture and cause a misfire. This is uncommon but possible on high-mileage engines.
• Low Compression: A mechanical issue like a burnt valve, a cracked valve spring, or a failing head gasket can cause a loss of compression, leading to a misfire. This is rare on the 2UZ-FE but would typically be accompanied by other symptoms and is a worst-case scenario. A compression test can confirm this.
• Damaged Wiring: The wiring harness or connector for the ignition coil or fuel injector on cylinder 8 could be damaged, often by rodents chewing on the wires, or from brittle plastic connectors breaking during other maintenance.
• Leaking Valve Cover Gasket / Spark Plug Tube Seal: The seals for the spark plug tubes in the valve cover can become brittle and leak oil directly into the spark plug well. This can saturate the ignition coil boot 🎬 See how to replace worn ignition coil boots. and foul the spark plug, causing a misfire. If you find oil in the spark plug well for cylinder 8, this is the likely cause.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0308 is the primary code present. Note any other codes.
2. Identify cylinder 8. It is the rearmost cylinder on the passenger's side of the engine, closest to the firewall. The passenger side bank is Bank 2 and contains cylinders 2, 4, 6, and 8, from front to back.
3. Swap the ignition coil from cylinder 8 with the coil from cylinder 6 (the next one forward on the same side). This is the easiest diagnostic test and requires only a 10mm socket.
4. Clear the codes with the scanner and start the engine. Let it idle and rev it slightly to see if the Check Engine Light returns.
5. Re-scan for codes. If the code is now P0306, the ignition coil you moved is bad and needs to be replaced.
6. If the code remains P0308, the coil is likely good. The next step is to check the spark plug. Remove the coil again and use a spark plug socket with an extension to remove the plug from cylinder 8. Inspect it for wear, oil fouling, or damage. If you find oil in the spark plug well, the valve cover tube seal has failed.
7. If the plug looks bad, replace all eight spark plugs. If it looks okay, you can swap it with another cylinder's plug (e.g., cylinder 6) to see if the code follows.
8. If the code persists on cylinder 8 after swapping the coil and plug, the issue is likely fuel, mechanical, or wiring related. Check the wiring and connector to the fuel injector and ignition coil for any damage. Listen for a steady clicking from the injector using a mechanic's stethoscope.
9. For a more advanced diagnosis, you would proceed to test the fuel injector signal with a noid light or perform a compression test on cylinder 8 to check for mechanical engine problems.

Parts You'll Likely Need

• Ignition Coil (OEM #90919-02230) — This is the most frequent failure point for a single-cylinder misfire on the 4.7L 2UZ-FE engine.
  Trusted brands: Denso (OEM) 673-1303, NGK (48991)
  OEM price range: $70-$100
  Aftermarket price range: $40-$70
• Spark Plugs (Set of 8) (OEM #90919-01210 (Denso SK20R11)) — Spark plugs are a maintenance item and a worn plug can cause a misfire. They should be replaced as a set. The OEM recommended plugs are Iridium. This part number is superseded by others but is widely recognized.
  Trusted brands: Denso (SK20R11), NGK (IFR6T11)
  OEM price range: $60-$90
  Aftermarket price range: $30-$60

Related Codes That Often Appear With This One

• P0300 — If the misfire is intermittent or affecting other cylinders randomly, a P0300 (Random/Multiple Cylinder Misfire) code may be stored alongside P0308.
• P030x (e.g., P0306, P0304) — If multiple cylinders on the same bank are misfiring (Bank 2 is even numbers: 2, 4, 6, 8), it could point to a shared problem like a clogged catalytic converter, a bad O2 sensor for that bank, or a timing issue.

Platform-Specific Known Issues

• Brittle Coil Connector Clips: After many years and heat cycles, the plastic clips that secure the wiring harness to the ignition coils become extremely brittle. It is very common for them to break when being disconnected. If the connector is not fully seated, it can cause a misfire. Some owners use a zip tie to secure a broken connector as a field repair.
• Timing Belt Job Induced Misfire: In some cases, misfires on Bank 2 (including P0308) have appeared after a timing belt replacement. This can be caused by damage to the crankshaft position sensor wiring during the job, or if the timing is off by a tooth on the passenger side cam gear.

Mechanic-Grade Diagnostic Values

• Ignition Coil Primary Resistance — expected: 0.36 - 0.55 Ω (Cold). Failure: A reading outside this range indicates a faulty coil.
• Ignition Coil Secondary Resistance — expected: 9.0 - 15.4 kΩ (Cold). Failure: A reading outside this range indicates a faulty coil.
• Fuel Injector Resistance — expected: 13.4 - 14.2 Ω at 68°F (20°C). Failure: Readings significantly outside this range suggest a failing injector coil.
• Fuel Pressure at Idle — expected: 38-44 psi (pre-2005 models), 44-50 psi (2005+ VVT-i models). Failure: Low fuel pressure can cause lean misfires, especially under load. High pressure is less common but may indicate a faulty regulator.

Hidden / Shadow Codes Worth Checking

• Mode $06, Test ID $0C: Provides raw misfire counts for each cylinder during the current or last driving cycle. This data can reveal intermittent misfires on cylinder 8 that haven't yet reached the threshold to set a solid P0308 code. (see via A capable OBD-II scanner that supports Mode $06 data, such as Toyota Techstream or advanced consumer tools like Torque Pro.)

Scan Tool Commands That Help

• Toyota Techstream: Active Test: Control the Injection Volume — This allows the technician to individually disable the fuel injector for cylinder 8. If the engine's idle does not change when cylinder 8's injector is disabled, it confirms that cylinder is not contributing, pointing to a problem with spark, fuel, or compression on that specific cylinder.
• Toyota Techstream: Data List: Misfire RPM / Misfire Load — After a P0308 code is stored, viewing this data shows the exact engine RPM and load conditions under which the misfire occurred. This helps in recreating the conditions to verify a fix.

Wiring & Ground Locations

• Engine Ground (Bank 2) — At the rear of the passenger side cylinder head, near the firewall where the engine mates to the transmission.. A corroded or loose main engine ground on Bank 2 can cause intermittent and weak spark for all cylinders on that side, including cylinder 8. This is often overlooked after transmission or exhaust work.
• Ignition Coil Connector (Cylinder 8) — 4-pin connector on the ignition coil for cylinder 8 (rearmost on passenger side). Pin 1 is 12V+ power, Pin 4 is ground. The trigger signal from the ECM is via the ground path.. Allows for testing of power, ground, and the IGF (Ignition Confirmation) signal at the coil itself. A break in the wire to the ECM for the IGT (Ignition Trigger) signal will prevent the coil from firing.
• ECM Pin IGT8 — This is the specific pin on the Engine Control Module (ECM) that sends the trigger signal for the cylinder 8 ignition coil (IGT8).. In rare cases of a persistent P0308 with a known-good coil, plug, and injector, a continuity test from this pin to the coil connector can rule out a wiring break. A faulty ECM driver is the last resort if the wire is good.

Real Owner Repair Stories

• Reddit user u/Sure-Survey-3444 (2006 Toyota Tundra, 308,xxx miles) — Recurring P0306 (Cylinder 6 Misfire), engine runs and sounds terrible when misfiring.
  ❌ Tried (didn't work) Replacing the spark plug and ignition coil for cylinder 6 (worked temporarily, then code returned)., Replacing ALL spark plugs and ignition coils (worked temporarily, then code returned).
  ✅ What actually fixed it The suggested fix, though the original poster did not confirm resolution, was to check the electrical connector for the fuel injector on that cylinder. The theory was that jostling the harness during the coil/plug changes temporarily restored the connection, causing the intermittent nature of the fault. Cleaning the contacts and adding injector cleaner was recommended.

OEM Part Supersession History

• 90919-02230 → This part number remains the primary reference for the ignition coil, but is also sold under Denso part number 673-1303. — N/A
  Heads up: Be aware of counterfeit Denso coils sold online. They often have incorrect branding, font, or plastic molding marks and are known to fail quickly. Purchase from reputable suppliers.

Model Year Variations Within This Range

• 2005-2006: In 2005, the 2UZ-FE engine was updated with Variable Valve Timing with intelligence (VVT-i) and an electronic throttle (ETCS-i). This increased power and complexity. While the fundamental cause of a P0308 (coil, plug, injector) remains the same, the VVT-i system adds another potential, though rare, cause for misfires if there is an oil pressure issue or phaser problem specific to Bank 2. The fuel pressure specification also changed for these later models.

Diagnostic Flowchart

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0306 — Cylinder 6 Misfire Detected. This code is frequently seen during the diagnostic process for P0308, as the universally recommended first step is to swap the cylinder 8 ignition coil with cylinder 6 to see if the misfire follows the coil.
• P0300 — Random/Multiple Cylinder Misfire Detected. Often appears alongside P0308 if the misfire is severe enough or if multiple cylinders are experiencing ignition coil or spark plug failures simultaneously.
• P1320 — Igniter Circuit Malfunction. This code has been reported by owners alongside P0308, indicating an electrical fault within the ignition system or coil wiring.
• P0302 — Cylinder 2 Misfire Detected. Related to Bank 2 (passenger side) misfires, which can sometimes be triggered collectively if the timing belt is off by a tooth on the passenger side cam gear.
• P0304 — Cylinder 4 Misfire Detected. Another Bank 2 companion code that shares the same passenger-side timing and wiring harness vulnerabilities as cylinder 8.

Frequently Asked Questions