P0304 on 2010-2013 GMC Savana: Cylinder 4 Misfire Causes and Fixes

What's Unique About the 2010-2013 Gmc SAVANA

On this generation of GMC Savana, a known issue is loose-fitting spark plug wires causing misfires. General Motors issued a Technical Service Bulletin (PIP4819A) specifically for this problem. Additionally, engine access is notoriously tight in these vans, making ignition system repairs more difficult and labor-intensive than on a pickup truck with the same engine. Mechanics often need to access the engine from both the interior 'doghouse' cover and through the front wheel wells. Some 5.3L engines are equipped with Active Fuel Management (AFM), and a failing AFM lifter on cylinder 4 can be a more serious, mechanical cause of this code.

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 idle
• Hesitation or stumbling during acceleration
• Flashing Check Engine Light
• Reduced engine power
• Decreased fuel economy
• Engine stalling
• Smell of unburned fuel from the exhaust

Most Likely Causes

1. Loose or Faulty Spark Plug Wire 🔴 High Probability → Shop Spark Plug A specific GM Technical Service Bulletin (PIP4819A) was issued for 2010-2013 models, citing loose spark plug wires as a direct cause for cylinder misfire codes, including P0304.
   How to confirm: Visually inspect the spark plug wire for cylinder 4. Check for a loose connection at both the ignition coil and the spark plug. Look for any signs of corrosion, burns, or physical damage to the wire's insulation.
   Typical fix: Replace the spark plug wire. 🎬 Watch: Step-by-step spark plug and wire replacement for this van. It is best practice to replace all spark plug wires as a set.
   Est. part cost: $50-$100
2. Worn or Fouled Spark Plug 🟡 Medium Probability → Shop Spark Plug Spark plugs are a standard maintenance item. If they are past their service life of up to 100,000 miles, they can easily cause a misfire.
   How to confirm: Remove the spark plug from cylinder 4 and inspect it. Look for a worn electrode, heavy carbon buildup, or oil fouling. To be certain, you can swap the cylinder 4 spark plug with one from another cylinder (e.g., cylinder 2). If the code changes to P0302, the spark plug is the culprit.
   Typical fix: Replace the spark plug. It is highly recommended to replace all spark plugs at the same time for even performance.
   Est. part cost: $8-$25 per plug
3. Failed Ignition Coil 🟡 Medium Probability → Shop Ignition Coil
   How to confirm: Swap the ignition coil from cylinder 4 with a coil from an adjacent cylinder (e.g., cylinder 2 on the same bank). Clear the codes and drive the vehicle. If the misfire code moves to the other cylinder (P0302), the ignition coil is faulty.
   Typical fix: Replace the failed ignition coil. 🎬 See how to replace the ignition coil on your Express.
   Est. part cost: $30-$75
4. Clogged or Faulty Fuel Injector ⚪ Low Probability → Shop Fuel Injector
   How to confirm: Listen to the injector with a mechanic's stethoscope to confirm it is clicking. A more definitive test is to swap the fuel injector with another cylinder, but this is a more labor-intensive job.
   Typical fix: Clean or replace the faulty fuel injector.
   Est. part cost: $50-$150

Rare But Worth Checking

• Failed Active Fuel Management (AFM) Lifter: → Shop Engine Valve Lifter On 5.3L V8 engines equipped with AFM, a lifter can become stuck or collapse, causing a persistent misfire on an AFM cylinder (1, 4, 6, or 7). This is a serious mechanical issue often accompanied by a ticking noise and can lead to camshaft damage if not addressed. 🎬 Watch: How to diagnose a failing AFM hydraulic lifter. Diagnosis requires removing the valve cover to inspect valve train movement and may require a compression test.
• Low Engine Compression: This is a serious mechanical issue. If ignition and fuel system checks do not reveal the problem, a compression test should be performed to check for issues like a bad valve, worn piston rings, or a leaking head gasket.
• Intake Manifold Gasket Leak: → Shop Engine Intake Manifold A vacuum leak near the intake runner for cylinder 4 can lean out the air/fuel mixture and cause a misfire. This can sometimes be detected by spraying starter fluid near the gasket with the engine running and listening for a change in idle speed.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner to confirm P0304 and check for any other codes.
2. Locate cylinder 4, which is the second cylinder from the front on the passenger side of the engine.
3. As per TSB PIP4819A, carefully inspect the spark plug wire for cylinder 4. Ensure it is securely connected at the coil and the spark plug. Check for any damage.
4. If the wire seems okay, swap the ignition coil from cylinder 4 with the coil from cylinder 2 (front passenger side). Clear the codes, run the engine, and see if the misfire code changes to P0302. If it does, the coil is bad.
5. If the misfire remains on cylinder 4, remove the spark plug. Inspect it for wear or fouling. Swap it with the plug from cylinder 2. If the code moves to P0302, the spark plug is bad.
6. If the misfire still remains on cylinder 4, the next step is to check the fuel injector. Listen for a steady clicking sound from the injector using a mechanic's stethoscope. A 'noid light' can be used to verify the injector is receiving an electrical pulse.
7. If ignition and fuel delivery seem correct, especially on a 5.3L engine, consider the possibility of a failed AFM lifter. Listen for a distinct ticking sound from the valve cover area.
8. Perform a compression test on cylinder 4 to rule out mechanical engine problems like a bad lifter, worn rings, or valve issues.

Parts You'll Likely Need

• Spark Plug Wire Set (OEM #9748UU) — This is the most likely cause, as identified by a manufacturer TSB. Wires are a common wear item, and due to difficult access, it's best to replace them as a set.
  Trusted brands: ACDelco, NGK, Delphi
  OEM price range: $70-$120
  Aftermarket price range: $40-$80
• Iridium Spark Plug (OEM #ACDelco 41-110 (GM 12680072)) — A worn or fouled spark plug is a very common cause for a single-cylinder misfire. They are a routine maintenance part. The OEM plug is Iridium and pre-gapped.
  Trusted brands: ACDelco, NGK
  OEM price range: $10-$20
  Aftermarket price range: $8-$15
• Ignition Coil (OEM #ACDelco D585) — Ignition coils are also a frequent failure point that can cause a P0304 code. Heat and vibration can cause them to fail over time. The D585 is a common coil for this engine family.
  Trusted brands: ACDelco, Delphi, Bosch
  OEM price range: $50-$90
  Aftermarket price range: $30-$75

Related Codes That Often Appear With This One

• P0300 — If the condition causing the P0304 is intermittent or beginning to affect other cylinders, a P0300 (Random/Multiple Cylinder Misfire Detected) code may also be stored. This is particularly common if the root cause is a failing AFM lifter.
• P0171/P0174 — If the misfire is caused by a vacuum leak, such as a bad intake manifold gasket, you may also see codes indicating the engine is running lean on one or both banks.

Technical Service Bulletins (TSBs) & Recalls

• PIP4819A: Addresses engine misfires due to loose spark plug wires.
• 19-NA-219: Discusses various causes for engine misfires and noises, including worn camshaft lobes and collapsed AFM lifters.

Platform-Specific Known Issues

• A GM Technical Service Bulletin (PIP4819A) directly addresses misfire codes (P0300-P0308) on these vehicles, pointing to loose spark plug wires as a primary cause that requires inspection and replacement.
• For models with the 5.3L V8, failure of the Active Fuel Management (AFM) system is a known issue. A collapsed or stuck lifter on cylinder 4 will cause a P0304 code and requires significant mechanical repair.

Mechanic-Grade Diagnostic Values

• Fuel Injector Resistance — expected: 10-18 Ohms (typically 10.5-16.5 Ohms). Failure: A reading outside the expected range, or a reading that deviates more than 0.5-1.0 Ohm from the other injectors, indicates a faulty injector.
• Fuel Pressure Drop (Injector Balance Test) — expected: Each cylinder should have a similar pressure drop when the injector is pulsed.. Failure: A pressure drop that is more than 1.5 PSI (10 kPa) different from the average of the other cylinders indicates a faulty or clogged injector.

Hidden / Shadow Codes Worth Checking

• Mode 6, Test ID $A2-$AF: These Test IDs correspond to misfire counts for each cylinder (Cylinder 1 through 8). Even if a P0304 code hasn't set, a technician can view these raw misfire counters on an advanced scan tool to see if cylinder 4 is accumulating misfires at a higher rate than others, indicating an emerging problem. (see via An OBD-II scan tool capable of displaying Mode $06 data.)

Scan Tool Commands That Help

• GDS2 / Tech2 or equivalent professional scanner: Cylinder Power Balance Test — This is a primary diagnostic step for a P0304. The tool deactivates each cylinder one by one and measures the corresponding drop in engine RPM. If deactivating cylinder 4 causes little or no RPM drop compared to other cylinders, it confirms cylinder 4 is not contributing power.
• GDS2 / Tech2 with Fuel Pressure Gauge (J39021): Fuel Injector Balance Test — Used to confirm if the fuel injector on cylinder 4 is delivering the correct amount of fuel. The scan tool pulses the injector for a set time while the technician observes the pressure drop on a connected fuel pressure gauge. An inconsistent drop compared to other cylinders points to a faulty injector.

Wiring & Ground Locations

• G102 — On the left rear of the engine block/cylinder head.. This is a primary ground point for the ignition coil banks. A loose or corroded G102 ground can cause weak spark and intermittent misfires across multiple cylinders, including cylinder 4.
• G103 — On the rear of the left-hand (driver's side) engine head.. This is another critical engine ground. A service bulletin for other electrical issues on the Savana platform specifically calls out ensuring G103 has a clean and tight connection. Poor grounding can affect sensor readings and ignition performance.
• Cylinder 4 Fuel Injector Wires — In the engine harness leading to the passenger side fuel rail, second injector from the front.. The power wire for all injectors is typically Pink (PNK). The control wire from the ECM for cylinder 4 is often Light Blue/Black (LT BLU/BLK), though wire colors can vary. Damage to these wires can prevent the injector from firing.

Real Owner Repair Stories

• Chevy/GMC P0300 Forum Discussion (2017 GMC Savana with V8 (similar engine and AFM system)) — Engine running badly, stumbling, ticking sound, and a P0300 code was present (often accompanies a single cylinder misfire like P0304).
  ❌ Tried (didn't work) The owner noted the issue was not a simple tune-up, implying spark plugs and wires were likely checked.
  ✅ What actually fixed it The root cause was a collapsed Active Fuel Management (AFM) lifter which had also damaged the camshaft. The repair required a new engine, which was covered under the powertrain warranty.

OEM Part Supersession History

• 10457730 → ACDelco D585 (GM 19005218, 12563293) — Standard part evolution and branding. The D585 is a widely recognized and cross-referenced part number for this style of GM ignition coil.

Model Year Variations Within This Range

• 2010-2013: While all V8 engines in this range (4.8L, 5.3L, 6.0L) are prone to the common ignition-related causes of P0304, the likelihood of an AFM lifter failure is specific to the 5.3L and some 6.0L engines. By 2013, all Vortec V8s came standard with Variable Valve Timing (VVT), adding complexity but not directly changing the primary causes of a P0304 code.