P0304 on Jeep: How to Diagnose & Fix
Cylinder 4 Misfire Detected
4 Jeep models · 8 documented issues · 5 critical · $100-$7,500 repair
P0304 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)
On early 3.6L Pentastar V6 engines, the LEFT cylinder head (cylinders 2-4-6) is prone to premature failure. Premature wear of the exhaust valve seats and guides (attributed to improper material/hardening) causes valve-seat recession, producing a tell-tale tick, misfires on the left bank and an illuminated check-engine light. Chrysler acknowledged the condition in TSB 09-002-14 and issued warranty extension X56 covering the left cylinder head for 10 years / 150,000 miles (per warranty bulletin D-14-12, June 2014); it was never a safety recall. A production fix (hardened valve guides/seats, revised left head casting, reman part RL141353AC / updated OEM casting) was phased in during summer 2012 (heads stamped 2062 = 206th day of 2012 or later are the fixed version), so the highest-risk population is 2011-2012 builds plus early-2012-build 2013 units. The dealer diagnostic per the TSB is a cylinder leak-down test, replacing the head at 25% or greater leakage.
Common Symptoms
- Engine ticking or tapping noise
- Single or multiple-cylinder misfire, rough idle
- Check engine light
- Loss of power / hesitation
- Failed compression or leak-down on a left-bank cylinder
How to Fix
Confirm the misfire is mechanical, not just a coil/plug, via compression or leak-down on the affected left-bank cylinder (TSB threshold: 25%+ leakage). The accepted repair is replacing the failed LEFT cylinder head with the revised casting (hardened valve guides/seats — reman RL141353AC or the updated OEM 'AD' casting), new head gasket and bolts, plus spark plugs and often coils. If the vehicle is within the X56 10-year/150,000-mile window, the dealer replaces the left head at no cost. Independents may rebuild/reseat a head, but the OE remedy is the redesigned head assembly.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Mopar left cylinder head with valvesOEMMopar 68141353AC (supersedes RL141353AC)
Confirm VIN/X56 status, exact left-bank leakage result, current supersession,
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- WarningDo not order a cylinder head from a tick or misfire code alone. FCA requires leakage testing on the cylinder that set the DTC and a result of at least 25 percent before this bulletin's head-replacement path applies.
- TipAsk the dealer to check the VIN for X56 status and repair history even though the original time limit may have expired; coverage was VIN-, time-, and mileage-dependent.
Sources for this issue (2)
The updated/'Upgrade' 3.6L Pentastar V6 (used on later WK2 and the WL fifth-gen) suffers premature wear of the intake rocker-arm high-lift sliders and/or intake camshaft high-lift lobes, traced by TSB to a manufacturing issue. As the rocker slider or cam lobe wears, the valve no longer opens fully, producing a distinct ticking noise and a misfire on the affected cylinder; if ignored the failing rocker can damage the camshaft. This is a separate failure from the early 2011-2013 left-head defect and from the 5.7 HEMI MDS lifter — it affects the V6 valvetrain across both generations.
Common Symptoms
- Cylinder-specific misfire code
- Ticking/tapping noise from the valvetrain
- Rough idle, hesitation, check-engine light
- Misfire that does not move when coil/plug is swapped
- Reduced power
How to Fix
Diagnose a cylinder-specific misfire accompanied by a valvetrain tick with a scope/inspection of the intake rocker arms and camshaft lobes. Replace worn rocker arms and, where the cam lobe is scored, the camshaft, per the applicable Pentastar Upgrade TSB; address promptly to avoid camshaft and follow-on damage. Replace spark plug/coil first only to rule out the easy cause — a persistent misfire with a tick is valvetrain, not ignition.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Mopar right intake-camshaft service kitOEMMopar 68661147AB
Complete FCA bulletin repair after right-bank intake high-lift lobe/rocker wear is confirmed Fitment/availability: 68661147AB supersedes 68661147AA and is the right-side kit named in TSB 09-011-25. Confirm VIN, ERC/ERG sales code, build/…
- Genuine Mopar left intake-camshaft service kitOEMMopar 68661146AA
Complete FCA bulletin repair after left-bank intake high-lift lobe/rocker wear is confirmed Fitment/availability: 68661146AA is the left-side kit named in TSB 09-011-25. Confirm VIN, ERC/ERG sales code, build/mileage scope and left-bank …
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- WarningDo not order a camshaft kit from a misfire code alone. FCA says the symptom may be related to cam/rocker wear, so the high-lift lobe and slider on the indicated bank must be inspected first.
- TipConfirm right versus left bank before ordering. FCA provides two different complete kits, and each already includes the camshaft, rocker arms, sealer, and gaskets for that side.
- WarningThe WL bulletin scope ends at the August 19, 2024 build cutoff even though model-year coverage extends through 2025. Verify the VIN/build record and ERC or ERG sales code.
Sources for this issue (1)
The 3.7L PowerTech V6 engine suffers from two common issues: cracked exhaust manifolds (causing ticking noise and exhaust leak) and valve cover gasket oil leaks. The cast iron exhaust manifolds develop stress cracks due to thermal cycling, with the passenger side being more common. Head gasket failures have also been reported on higher-mileage engines.
Common Symptoms
- Ticking noise from engine on cold start
- Exhaust smell in cabin
- Oil leak on valve covers
- Oil spots on driveway
- Reduced fuel economy
- Check engine light for exhaust leak codes
How to Fix
For exhaust manifold: Replace cracked manifold with new OEM or aftermarket unit ($200-400 per side, $400-800 labor). For valve cover gaskets: Replace both gaskets using Mopar 53021828AB gasket set ($20-40 parts, $200-400 labor). Use Permatex Ultra Grey sealant on the half-moon seals. For head gasket: If coolant mixes with oil, head gasket replacement needed ($1,500-2,500).
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Mopar 53013692AB passenger/right exhaust manifoldOEMMopar 53013692AB
Right exhaust-manifold replacement after inspection proves that side is cracked or damaged Fitment/availability: 2005-2012 Jeep Liberty 3.7L, passenger/right side, superseding 53013692AA. Not the left manifold and not approved for 2002-2…
- Genuine Mopar 53013691AC driver/left exhaust manifoldOEMMopar 53013691AC
Left exhaust-manifold replacement after inspection proves that side is cracked or damaged Fitment/availability: 2005-2012 Jeep Liberty 3.7L, driver/left side catalog branch. Not the right manifold and not approved for 2002-2004 without V…
- Genuine Mopar 53013932AB passenger/right exhaust-manifold gasketOEMMopar 53013932AB
Do not substitute for the left gasket.
- Genuine Mopar 53013933AB driver/left exhaust-manifold gasketOEMMopar 53013933AB
Do not substitute for the right gasket.
- Fel-Pro VS50518R valve-cover gasket setOEMFel-Pro VS50518R
Valve-cover gasket replacement after the cleaned engine proves a cover leak on the early 3.7L branch Fitment/availability: 2002-2005 Jeep Liberty 3.7L listing. Confirm exact cover material, included grommets and VIN because 2005 overlaps…
- Fel-Pro VS50652R valve-cover gasket setOEMFel-Pro VS50652R
Both-cover gasket replacement after the cleaned engine proves a cover leak on the later plastic-cover branch Fitment/availability: 2005-2012 Jeep Liberty 3.7L with plastic valve covers and included grommets. Confirm exact cover material/…
- Genuine Mopar 53020989AB 3.7L cylinder-head gasketOEMMopar 53020989AB
Confirm side, full gasket/bolt req
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- TipThe ticking on cold start that goes away when warm is almost always a cracked exhaust manifold - not lifter noise
Sources for this issue (3)
The 3.7L SOHC V6 shares its valvetrain architecture with the 4.7 and inherits its worst habit: the stamped rocker arm sits on a hydraulic lash adjuster and is retained only by valve-spring pressure. When the lash adjuster bleeds down or seizes - typically from extended oil-change intervals, low oil level or oil coking - the rocker loses its perch and falls off the valve tip. The engine first develops a light tick at idle, which owners and shops routinely misdiagnose as normal lifter tap, then progresses to a hard tap, a dead cylinder and in the worst Commander cases a rocker that has beaten its way through the valve cover. This is a distinct failure from the 4.7's valve-seat problem, and it does not apply to the 5.7 Hemi, which uses a pushrod valvetrain with a completely different rocker design.
Common Symptoms
- Ticking or tapping from top of engine, worst at idle
- Tick escalating to a hard knock over weeks
- Misfire on one cylinder
- Check engine light
- Oil leak from a cracked valve cover in extreme cases
- Cold-start rattle from timing chain area (separate, related timing-chain wear)
How to Fix
Do not dismiss a new tick on a 3.7 as lifter noise. Pull the valve covers early - it is a comparatively cheap inspection - and look for a rocker off its lash adjuster or an adjuster that will not pump up. Caught early the fix is replacing the affected rocker arms and lash adjusters, checking the cam lobe for wear, and correcting the oiling problem that caused it (short oil-change intervals with the correct 5W-30, and verifying the oil pickup and filter are not restricted). Left alone the rocker chews the cam lobe and valve tip, escalating to cylinder head or engine replacement. Related: the same engine family's timing chain tensioner and nylon chain guides wear and produce a cold-start rattle, so inspect the chain and tensioner while the front of the engine is apart on higher-mileage examples. No recall covers either failure.
Sources for this issue (3)
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)
P0304 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 P0304 mean on a Jeep?
P0304 stands for "Cylinder 4 Misfire Detected." This code means the engine computer detected a misfire in cylinder number 4 — that cylinder isn't igniting its air-fuel mixture fully or at all. The system detects this by monitoring small changes in crankshaft rotation speed as each cylinder fires. You may feel a rough idle, shaking, hesitation or reduced power, and a persistent misfire can dump unburned fuel into the exhaust and overheat or damage the catalytic converter. Since it's pinpointed to one cylinder, the problem typically lies in that cylinder's spark, fuel, or compression. On Jeep it is documented across 4 models: Grand Cherokee, Liberty, Commander, Wrangler.
What are the most common causes of P0304?
The most common causes of P0304 are: Worn or fouled spark plug in cylinder 4, Failed or weak ignition coil on cylinder 4, Faulty spark plug wire or boot (where applicable), Clogged, stuck or leaking fuel injector for cylinder 4, Vacuum or intake air leak near that cylinder, Low compression (worn rings, burnt/leaking valve, head gasket), Damaged wiring or connector at the coil or injector. The specific cause varies by vehicle.
How much does it cost to fix P0304 on a Jeep?
Published repair estimates on Jeep range from $100 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 P0304 on a different make?
View P0304 across all makes →Join 700+ subscribers following Au7o for vehicle insights and updates.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.