P0307 - Cylinder 7 Misfire on the GM 5.3L V8
| Light color | Amber |
|---|---|
| Urgency | Service soon (amber) - Stop now if light is flashing |
| Safe to drive | Short distance only if light is steady; stop immediately if flashing |
| Common cause | Failed AFM lifter (GM 5.3 specific) or worn ignition coil |
| DIY or shop | Either - coil/plug is DIY; lifter repair requires a shop |
P0307 means the ECM detected a misfire in cylinder 7. On GM's 5.3L V8 (found in the Silverado, Sierra, Tahoe, Yukon, and Suburban from roughly 2007 onward), cylinder 7 sits at the rear of the driver-side (left) bank. It fires third in the sequence 1-8-7-2-6-5-4-3, and it is one of four cylinders controlled by the Active Fuel Management (AFM) system - which makes it a disproportionately common misfire location.
Start with the cheap and easy suspects first: ignition coil, spark plug, and fuel injector. If swapping those parts does not move or clear the misfire, the problem is likely mechanical - a collapsed AFM lifter or a failed Valve Lifter Oil Manifold (VLOM). That repair is more involved and costly.
Where is cylinder 7 on the 5.3L V8?
GM numbers its V8 cylinders with odd numbers on the driver side (Bank 1) and even numbers on the passenger side (Bank 2). The layout is:
- Driver side (Bank 1): 1 (front) - 3 - 5 - 7 (rear)
- Passenger side (Bank 2): 2 (front) - 4 - 6 - 8 (rear)
Cylinder 7 is therefore the rearmost cylinder on the driver side, close to the firewall. The firing order is 1-8-7-2-6-5-4-3, so cylinder 7 is the third to fire. Its location near the firewall makes spark plug access awkward on trucks; a short socket extension and a swivel often help.
- Check Engine Light (MIL)Amber
- Meaning: ECM stored a misfire fault on cylinder 7; steady amber means stored fault, flashing means active misfire occurring right nowRecommended action: Scan for codes immediately; if flashing, stop driving to avoid catalytic converter damage
Common causes on the 5.3L
The 5.3L has a known hierarchy of misfire causes, and cylinder 7 sits at the intersection of both ignition-related failures and a specific mechanical weakness tied to the AFM system.
Ignition coil: Coil-on-plug designs on the 5.3L see coils fail with age and heat. A coil that measures acceptable resistance at room temperature can still break down under load. This is the first thing to rule out because the test costs nothing - swap the coil from cylinder 7 with a neighboring coil (cylinder 5 is accessible), clear the code, and drive. If the code shifts to P0305, the coil is bad.
Spark plug: The factory AC Delco plugs are designed for 100,000-mile service intervals, but heat cycles and gap erosion cause misfires well before that on high-mileage engines. Pull the cylinder 7 plug and check for excessive wear, deposits, or a cracked porcelain tip. Replace with an OEM-specification plug.
Fuel injector: A clogged or electrically failed injector starves cylinder 7 of fuel. Listen for a clicking pulse from the injector with a mechanic's stethoscope. A noid light confirms the ECM is still sending a signal. If the signal is present but the injector is not clicking, the injector is faulty.
AFM lifter collapse (5.3-specific): The Active Fuel Management system uses special hydraulic lifters on cylinders 1, 4, 6, and 7 that intentionally collapse to shut those cylinders off during light throttle. When oil pressure is too low, the oil is dirty, or the solenoids in the VLOM (Valve Lifter Oil Manifold) stick open, the lifter collapses and stays collapsed. The valve stops opening, the cylinder stops firing, and the ECM logs P0307. A ticking or tapping noise from the driver-side valve cover is a strong indicator. A compression test on cylinder 7 will show low or zero compression when the lifter has failed mechanically.
Low oil pressure / dirty oil: AFM lifters are extremely sensitive to oil condition. Low oil level, extended oil change intervals, or using the wrong viscosity can trigger lifter collapse. Check oil level and condition before any other diagnosis on high-mileage 5.3L engines.
How to diagnose P0307 step by step
Work through these steps in order to avoid unnecessary parts spending.
1. Read and record all codes. Connect an OBD-II scanner. Note whether P0307 is stored or pending, and whether P0300 (random misfire) appears alongside it. P0300 with P0307 suggests the problem is mechanical or oil-related; P0307 alone points toward ignition or injector.
2. Check oil level and condition. Low or black, sludgy oil is a quick route to AFM lifter failure. If the oil is due for a change, do it before continuing. Use the GM-specified 0W-20 or 5W-30 grade.
3. Swap the ignition coil. Move the coil from cylinder 7 to an adjacent cylinder (5 or 3). Clear codes and drive for 10-15 minutes under load. If the misfire code follows the coil to the new cylinder, replace the coil.
4. Inspect and swap the spark plug. If the coil test does not move the misfire, remove the cylinder 7 plug. Look for heavy carbon deposits, a closed gap, or physical damage. Replace with an OEM AC Delco or equivalent plug gapped to spec (typically 0.040 in on the 5.3L).
5. Test the fuel injector. Use a stethoscope or mechanic's probe to listen for the injector clicking. A noid light confirms the driver signal. A dead-clicking injector or one with clogged spray pattern needs replacement or professional cleaning.
6. Perform a compression test. If the above three checks do not resolve the misfire, do a wet-and-dry compression test on cylinder 7. A reading below roughly 120 psi (or more than 20% lower than adjacent cylinders) points to a collapsed lifter or a valve seating problem.
7. Check for AFM lifter collapse. With the valve cover off, observe the cylinder 7 rocker arms at idle. Both rocker arms should move with each engine revolution. If neither rocker moves, the lifter has collapsed. At that point, the VLOM and the affected lifters need replacement. Many shops also recommend replacing the AFM lifters on cylinders 1, 4, and 6 at the same time since they share the same wear pattern.
Repair options and costs
Coil replacement: Aftermarket coils run $40-$80 each; OEM GM coils are $60-$120. DIY time is under 30 minutes per coil.
Spark plug replacement: A set of eight AC Delco Iridium plugs costs $60-$100. Budget an hour for a DIY job on a truck with good access to all cylinders.
Fuel injector: Remanufactured injectors cost $50-$150 each. Replacement is straightforward but requires fuel-rail depressurization; most DIYers with basic experience can do it.
VLOM replacement: The Valve Lifter Oil Manifold itself costs $150-$300. Replacing just the VLOM without the lifters is worth trying first if the lifters are not mechanically collapsed - a faulty solenoid inside the VLOM is sometimes the root cause. If the lifters have collapsed, replace them at the same time.
AFM lifter replacement: This is the expensive repair. Parts for a full AFM lifter set plus VLOM run $400-$600. Labor adds $800-$1,500 at a shop (intake manifold removal and partial valve train teardown are required). Total shop bills of $1,500-$2,500 are common.
AFM delete: Owners who have already paid for one lifter job often convert the engine to a solid (non-AFM) lifter setup at the same time. A cam-and-lifter delete kit costs $400-$600 in parts; combined with an ECM tune to disable AFM in software, the engine runs in V8 mode permanently and the failure mode is eliminated. Fuel economy drops by roughly 1-2 mpg compared to advertised AFM figures, but real-world differences are small since AFM only activates in light highway cruise.
Frequently Asked Questions
Q: Can I drive with a P0307 code on a GM 5.3?
A: If the check-engine light is steady amber, you can drive short distances to reach a shop, but the engine is running rough and fuel economy will suffer. If the light is flashing, stop as soon as safely possible - an active misfire pushes unburned fuel into the catalytic converter and will destroy it within a few miles of continued driving.
Q: Is cylinder 7 an AFM cylinder on the GM 5.3?
A: Yes. The 5.3L AFM system deactivates cylinders 1, 4, 6, and 7. Cylinder 7 is one of four that carry the special collapsible AFM lifters. This is why P0307 on a 5.3L warrants a compression test and oil-condition check even if the coil and plug appear fine - a collapsed lifter is a real possibility, especially on engines with 80,000 or more miles.
Q: How do I know if my 5.3 has a collapsed AFM lifter vs. a bad coil?
A: The fastest indicator is engine noise: a collapsed lifter typically produces a distinct tick or tap from the driver-side valve cover at idle. A bad coil produces no unusual noise. Confirm with a compression test - a collapsed lifter leaves cylinder 7 with very low or zero compression, while a coil or plug failure leaves compression normal. Swapping the coil to an adjacent cylinder is free and takes 10 minutes; do that first before opening the engine.
Q: What does a GM 5.3 AFM lifter replacement cost?
A: Plan on roughly $1,500-$2,500 at a shop for parts and labor, covering the VLOM, AFM lifters, gaskets, and oil change. Some owners spend more if the camshaft shows wear from lifter debris. An AFM delete at the same time adds $400-$600 in parts plus a tune, but eliminates the chance of a repeat failure.
Q: Will replacing the VLOM fix my cylinder 7 misfire without touching the lifters?
A: Sometimes, yes. If the VLOM solenoid is stuck open but the lifter itself has not yet collapsed mechanically, a new VLOM restores correct oil pressure to the lifter and it may re-extend. However, if the lifter has already failed internally, the VLOM alone will not fix it. A compression test tells you which situation you are in: normal compression means the lifter is still functional, and the VLOM is worth trying first.