P0308 on Jeep: How to Diagnose & Fix
Cylinder 8 Misfire Detected
2 Jeep models · 2 documented issues · 1 critical · $2,200-$7,500 repair
P0308 on Jeep by model: symptoms, diagnosis and fix
HEMI-equipped Grand Cherokees can develop the characteristic MDS lifter tick. This ticking noise is most noticeable at idle and during light throttle. While often not immediately harmful, it indicates lifter wear from the MDS cylinder deactivation system.
Common Symptoms
- Ticking noise at idle
- Tick follows engine RPM
- Noise from top of engine
- Tick more pronounced when warm
- Noise comes and goes
How to Fix
Use quality synthetic oil meeting Chrysler MS-6395 spec. Consider MDS delete kit for permanent solution. Some owners have replaced lifters and camshaft under extended warranty. Regular oil changes help minimize tick progression.
Owner tips & cautions
- TipRegular oil changes help minimize tick progression.
- TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
Sources for this issue (1)
The 4.7L SOHC PowerTech V8 (2006-2009 Commander) presses hard steel valve seats into aluminum cylinder heads. Any overheat event - and the XK's cooling system is itself a weak point - lets the aluminum head grow away from the seat, loosening it. The seat then drops into the combustion chamber, or the head cracks between the valve seats. The failure is usually sudden: a healthy-running engine develops a violent single-cylinder misfire, a hammering noise and total loss of compression in that hole within minutes. Commander owners report it most often on the 4.7 after a cooling-system incident, and Chrysler's 2005-2007 4.7 heads are the ones most cited. Compression on the dead cylinder reads near zero; a borescope shows the seat lying on the piston crown or a valve pocket that has been pounded out.
Common Symptoms
- Sudden severe misfire on one cylinder
- Flashing check engine light
- Loud knocking or hammering from one bank
- Near-zero compression in the affected cylinder
- Complete loss of power / engine barely idles
- Rough running that appears without warning
How to Fix
There is no recall and no free remedy. Diagnose with a compression or leakdown test plus a borescope before spending money on coils and injectors - a dropped seat will not respond to a tune-up. The repair is cylinder head replacement (both heads are usually done together on high-mileage engines, since the other side has the same seats and the same heat history), with valve-to-piston damage often forcing piston or short-block replacement as well. Many owners with 150k+ miles find a used or remanufactured long block is cheaper than a head job plus machine work. Preventively, the single best defense is to treat any overheat, coolant loss or hot-running episode as an emergency and to keep the cooling system - radiator, thermostat, water pump, fan clutch - in good order, because overheating is the documented trigger.
Sources for this issue (3)
P0308 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0308 mean on a Jeep?
P0308 stands for "Cylinder 8 Misfire Detected." P0308 means the engine computer detected a misfire on cylinder number 8 — that cylinder is failing to combust properly or at the correct time. The PCM identifies it by monitoring crankshaft speed variations as cylinder 8 fires. Misfires waste fuel, increase emissions, and can overheat and damage the catalytic converter, so a hard misfire may cause a flashing check engine light. Typical symptoms include rough idle, vibration, hesitation, and reduced power. On Jeep it is documented across 2 models: Grand Cherokee, Commander.
What are the most common causes of P0308?
The most common causes of P0308 are: Worn, fouled, or incorrectly gapped spark plug on cylinder 8, Failed ignition coil or coil-on-plug for cylinder 8, Faulty, clogged, or leaking fuel injector, Vacuum or intake air leak affecting that cylinder, Low compression (worn rings, burnt/leaking valve, head gasket), Damaged spark plug wire or boot (on applicable engines), Carbon buildup or sticking valve. The specific cause varies by vehicle.
How much does it cost to fix P0308 on a Jeep?
Published repair estimates on Jeep range from $2,200 to $7,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0308 on a different make?
View P0308 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.