P0308 on 2009-2013 GMC Savana: Cylinder 8 Misfire Causes and Fixes

What's Unique About the 2009-2013 Gmc SAVANA

For the 2009-2013 GMC Savana with a V8 engine, a P0308 code must be taken seriously. While standard ignition or fuel issues are possible, these engines, particularly those with Active Fuel Management (AFM), have a well-documented history of lifter failure. A collapsed or stuck AFM lifter is a frequent cause of single-cylinder misfires on this platform, which can lead to further damage to the camshaft if not addressed. This mechanical issue is much more severe than a simple spark plug or coil replacement and is specifically referenced in GM Technical Service Bulletin #PIP4138R as a potential cause for misfire codes after basic diagnostics fail.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Rough or shaking engine idle.
• Hesitation or stumbling during acceleration.
• Noticeable loss of engine power.
• Flashing or solid Check Engine Light.
• A ticking, chirping, or squealing sound from the engine, often at half the speed of the crankshaft, which strongly indicates a lifter or camshaft issue.
• Reduced fuel economy.
• Smell of unburnt fuel from the exhaust.

Most Likely Causes

1. Faulty Ignition Coil 🔴 High Probability Heat and vibration in the engine bay can cause ignition coils to fail over time. Cylinder 8 is located at the rear of the engine on the passenger side 🎬 Watch: Locating and diagnosing a cylinder 8 misfire on a Savana, an area that can sometimes be exposed to external factors like dripping coolant from heater core connections, as noted by some owners.
   How to confirm: Swap the ignition coil from cylinder 8 with another cylinder (e.g., cylinder 6, which is easier to access). Clear the codes and drive the vehicle. If the code changes to P0306, the ignition coil is faulty.
   Typical fix: Replace the faulty ignition coil. It is often recommended to replace the spark plug at the same time. The OEM part is typically ACDelco.
   Est. part cost: $40-$80
2. Worn or Fouled Spark Plug 🔴 High Probability Spark plugs are a standard maintenance item. Oil consumption, a known issue on some AFM engines, can also lead to premature fouling of the spark plugs.
   How to confirm: Remove and inspect the spark plug from cylinder 8. Look for signs of wear, carbon or oil fouling, or damage to the electrode. Compare it to a plug from a working cylinder.
   Typical fix: Replace the spark plug. If all plugs are near their service interval (typically 100,000 miles for iridium plugs), it's best to replace the entire set.
   Est. part cost: $5-$20
3. Failed AFM Lifter / Worn Camshaft 🟡 Medium Probability V8 engines in this era with Active Fuel Management (AFM/DOD) are notorious for lifter failures. The complex AFM lifters can become stuck, collapse, or damage the camshaft lobe, preventing proper valve operation. This is a widely discussed issue in owner forums.
   How to confirm: This is an advanced diagnosis. Listen for a persistent ticking or chirping noise that is distinct from a simple exhaust leak. A mechanic will perform a compression test and may need to visually inspect the valvetrain (lifters, pushrods, and camshaft) by removing the valve cover and intake manifold. Measuring valve lift can also confirm the issue. 🎬 See how a mechanic diagnoses AFM lifter noise and failure
   Typical fix: Requires replacing the set of lifters for the affected cylinder bank (or all 16), and often the camshaft if it has been damaged. The Valve Lifter Oil Manifold (VLOM) is also frequently replaced. Many owners opt for an 'AFM delete' kit at this time, which replaces AFM components with standard, more reliable parts. This repair can cost several thousand dollars. 🎬 Watch: Step-by-step guide to replacing lifters and removing the cylinder head
   Est. part cost: $500-$1500
4. Faulty Fuel Injector ⚪ Low Probability
   How to confirm: Check for a pulse signal at the injector with a 'noid' light. You can also swap the injector with another cylinder to see if the misfire follows, though this is more labor-intensive than swapping a coil.
   Typical fix: Replace the faulty fuel injector for cylinder 8.
   Est. part cost: $50-$120

Rare But Worth Checking

• Intake Manifold Gasket Leak: A vacuum leak near the cylinder 8 intake runner can lean out the air/fuel mixture and cause a misfire. This would typically be accompanied by a lean code (P0171/P0174).
• Low Engine Compression: Caused by issues like a worn piston ring, a leaking head gasket, or a problem with the cylinder head valves (e.g., broken valve spring). A compression test is required for diagnosis.
• Coolant Leak onto Ignition Components: In some GM trucks and vans, the heater core quick-connect fittings are located on the firewall above the cylinder 8 area. A slow leak can drip coolant onto the spark plug wire and coil, causing a misfire.

Diagnosis Steps

1. Use an OBD-II scanner to confirm the P0308 code and check for any other stored codes. Note if the Check Engine Light is flashing.
2. Visually inspect the ignition system for cylinder 8 (rear passenger side). Check for a loose coil connector, damaged wiring, a loose spark plug wire, or any signs of moisture/coolant from above.
3. Swap the ignition coil from cylinder 8 with a known good cylinder (like cylinder 6). Clear the codes and run the engine to see if the misfire code moves to the new cylinder (P0306). If it does, the coil is bad.
4. If the misfire does not move, inspect and replace the spark plug for cylinder 8. Check for excessive wear, damage, or oil/carbon fouling.
5. Listen carefully to the engine for any ticking, tapping, or chirping sounds. A distinct valvetrain noise that increases with RPM points towards a mechanical issue like a lifter.
6. Check the fuel injector pulse on cylinder 8 using a noid light. If the pulse is present, consider swapping the injector with another cylinder, though this is more labor-intensive.
7. Perform an engine compression test on cylinder 8 to rule out mechanical sealing issues (rings, valves, head gasket). Compare the reading to other cylinders.
8. If all other tests pass and especially if a ticking noise is present, proceed with a mechanical inspection of the valvetrain (lifters and camshaft), as recommended by TSB #PIP4138R. This involves removing the valve cover to check for proper valve movement.

Parts You'll Likely Need

• Ignition Coil (OEM #ACDelco D581 (UF271)) — This is one of the most common electrical failure points causing a single-cylinder misfire.
  Trusted brands: ACDelco, Delphi, NGK
  OEM price range: $60-$90
  Aftermarket price range: $35-$65
• Spark Plug (OEM #ACDelco 41-110 (Iridium)) — Spark plugs are a routine maintenance item and a frequent cause of misfires as they wear out.
  Trusted brands: ACDelco, NGK
  OEM price range: $10-$20
  Aftermarket price range: $5-$15
• AFM Valve Lifter Set (OEM #ACDelco 12648846 (Set of 8 AFM lifters)) — A known failure point on these GM V8 engines. A collapsed or stuck lifter directly causes a misfire and requires replacement. It is recommended to replace all AFM lifters at once.
  Trusted brands: ACDelco, Melling
  OEM price range: $200-$400
  Aftermarket price range: $150-$300
• Camshaft — A failed lifter can quickly damage the corresponding lobe on the camshaft, requiring both to be replaced.
  Trusted brands: ACDelco, Melling, COMP Cams
  OEM price range: $300-$500
  Aftermarket price range: $200-$400
• AFM Delete Kit — A popular, permanent solution to prevent future AFM lifter failures. These kits typically include a non-AFM camshaft, standard lifters, a new valley cover, and necessary gaskets.
  Trusted brands: Texas Speed, Brian Tooley Racing, Melling
  OEM price range: N/A
  Aftermarket price range: $500-$1200

Related Codes That Often Appear With This One

• P0300 — If the underlying cause, such as a failing fuel pump or a failing AFM system, begins to affect multiple cylinders, a P0300 (Random Misfire) code may appear alongside P0308.
• P050D — As noted in TSB #PIP5628G, this code for 'Rough Idle Off Cold Start' can accompany misfire codes and points towards a deeper diagnostic process related to potential mechanical engine issues.

Technical Service Bulletins (TSBs) & Recalls

• PIP4138R: Advises technicians to check for a worn camshaft lobe and/or lifter if standard diagnostics do not resolve a P0300-P0308 misfire code. It specifically mentions listening for a chirp, squeak, or tick noise.
• PIP5628G: Notes that codes P0300-P0308 can be seen with code P050D (Rough Idle Off Cold Start) and provides information for diagnosis.
• 19-NA-219: A later bulletin that consolidates information and also points to worn cam/lifters, sticking valves, and collapsed AFM lifters as potential causes for P0300-series misfires.

Platform-Specific Known Issues

• The V8 engines equipped with Active Fuel Management (AFM) in this generation of Savana vans are highly susceptible to lifter failure. A collapsed or stuck AFM lifter is a primary cause of single-cylinder misfires that goes beyond simple tune-up parts. This failure often requires replacement of the lifters and the camshaft, representing a major and expensive repair.

Mechanic-Grade Diagnostic Values

• Fuel Pressure (Key On, Engine Off) — expected: 50 - 65 PSI. Failure: Pressure below 50 PSI can indicate a weak fuel pump.
• Ignition Coil Primary Resistance — expected: 0.4 - 2.0 Ohms. Failure: A reading of infinite ohms (open) or near zero (short) indicates a failed coil.
• Ignition Coil Secondary Resistance — expected: 6,000 - 10,000 Ohms. Failure: A reading significantly outside this range suggests the internal windings are compromised.
• Fuel Injector Resistance — expected: ~12.5 Ohms (High Impedance). Failure: A reading that deviates more than 0.5-1.0 Ohm from the other injectors, or is open/shorted, indicates a faulty injector.
• AFM System Oil Pressure (via Scan Tool) — expected: >25 PSI at hot idle. Failure: Pressure at or below 19 PSI at hot idle suggests a problem with the VLOM, its filter screen, or overall engine oil pressure, which can cause AFM lifter failure.
• Running Compression Test — expected: 60 - 90 PSI (and consistent across cylinders). Failure: A cylinder with significantly lower running compression, especially if a lifter is collapsed, will not build as much pressure as a healthy cylinder.

Hidden / Shadow Codes Worth Checking

• Misfire Current/History Counters: These are not standard DTCs but live data parameters that show the exact number of misfire events per cylinder over the current and previous drive cycles. A high count on cylinder 8 confirms the P0308 is active and severe. (see via GM's Tech 2 or GDS2 software. Many professional-grade aftermarket scan tools can also access this data under engine live data.)
• Mode $06, TID $A9-$B0: Mode $06 data can show misfire counts for each cylinder during the last 10 driving cycles. For GM CAN-bus vehicles, Test IDs (TID) from $A9 (Cylinder 1) to $B0 (Cylinder 8) correspond to these misfire counts. This can reveal intermittent misfires that haven't yet set a hard code. (see via Any scan tool that supports Mode $06 diagnostics. The data is presented in raw hexadecimal and must be converted.)

Scan Tool Commands That Help

• GM Tech 2 / GDS2 or equivalent: Power Balance Test — This is a critical diagnostic step. It allows the user to disable the fuel injector to cylinder 8 and observe the RPM drop. If there is little or no drop in RPM when cylinder 8 is deactivated, it confirms that cylinder is not contributing power.
• GM Tech 2 / GDS2: Fuel Injector Balance Test — This test is used to isolate a clogged or weak fuel injector. The tool pressurizes the fuel rail, then fires each injector for a precise duration. It measures the pressure drop for each event. If the pressure drop for cylinder 8 is significantly less than the others, the injector is likely restricted.
• GM Tech 2 / GDS2 or equivalent: AFM Solenoid Control — When an AFM lifter failure is suspected, this command can be used to manually command the VLOM solenoids on and off (engine running) to check for a response, helping to diagnose a faulty solenoid in the Valve Lifter Oil Manifold.

Wiring & Ground Locations

• G103 — On the front of the passenger side cylinder head.. This is a primary engine ground. A poor connection here can cause erratic behavior from sensors and modules, including the ECM, potentially leading to false misfire detection or issues with ignition/fuel control.
• G104 — On the rear of the driver's side cylinder head.. Another critical engine-to-chassis ground. Given its location, it can be susceptible to corrosion or damage. A bad ground here can affect the entire engine management system.
• Cylinder 8 Injector Control Wire — Pin J2-48 at the ECM connector, typically a Light Blue/Red wire.. When diagnosing a fuel-related P0308, if a noid light shows no pulse at the injector, a continuity test must be run on this wire between the injector connector and the ECM to rule out a wiring break.
• G200 / G201 — Behind the left kick panel, inside the cabin.. These are main instrument panel and body grounds. While less likely to cause a single-cylinder misfire, a poor connection could affect ECM power or communication, leading to various unpredictable issues.

Real Owner Repair Stories

• ScannerDanner Forum User (2016 GMC Sierra 5.3L (similar engine platform)) — Flashing P0308 code, rough running.
  ❌ Tried (didn't work) A GM dealership performed a major repair under warranty, replacing the camshaft and all lifters due to a confirmed collapsed lifter on cylinder 8.
  ✅ What actually fixed it The P0308 code returned just two days after the expensive camshaft and lifter replacement. The owner suspected an underlying issue was missed by the dealer, such as a bent or sticking valve, which was not addressed during the initial repair. This highlights the importance of comprehensive mechanical checks (like a leak-down test) even when a common failure like a lifter is found.
• GRRRR8.net Forum User (Pontiac G8 (LS-family V8 engine)) — Rough idle, slight misfire at cruise, and a loud squeal from the engine, with a cylinder misfire code.
  ❌ Tried (didn't work) Swapping the ignition coil and spark plug wire did not resolve the issue.
  ✅ What actually fixed it Tearing down the engine revealed a failed roller bearing on a lifter. The seized roller had destroyed the corresponding camshaft lobe. The final fix was replacing the camshaft and all 16 lifters. This confirms the failure pattern where a bad lifter leads to camshaft destruction.

When the Usual Fixes Don't Work

• In one documented case involving a similar GM truck, a dealership replaced the camshaft and lifters to fix a P0308 caused by a collapsed lifter, but the code returned almost immediately. This suggests that while the lifter/cam failure is a very common cause, it can sometimes be a symptom of another problem (like a valve sealing issue or oil pressure problem) that, if missed, will lead to a repeat failure or persistent code. A comprehensive diagnosis is key, even when a 'common' cause is found.

OEM Part Supersession History

• 12648846 → 12698945 or 12740071 — GM has updated the AFM lifter design multiple times to improve reliability and address the high failure rate.
  Heads up: While physically interchangeable, it is critical to use the latest available part number when replacing lifters to get the most recent design improvements. Always replace lifters as a full bank or full set.
• Multiple older numbers → 12571609 (VLOM / Valve Lifter Oil Manifold) — An updated VLOM was released by GM to help address oil pressure and solenoid issues that contributed to AFM lifter failure.
  Heads up: When performing an AFM lifter replacement, it is highly recommended to also replace the VLOM with the updated part to ensure proper oil delivery and prevent a repeat failure.

Model Year Variations Within This Range

• 2009-2013: The core engine architecture (Gen IV LS-based V8s like the LMG, LC9, etc.) and the problematic Active Fuel Management (AFM) system are consistent across this entire range for the Savana. The significant engine platform change to the EcoTec3 family occurred in 2014 for other GM trucks, but the Savana platform often lags behind. For the purpose of diagnosing a P0308, the causes and procedures are largely identical for all 2009-2013 V8 models.