P0304 on Acura
Cylinder 4 Misfire Detected
P0304 on Acura vehicles indicates cylinder 4 misfire detected. Au7o has documented this code across 3 Acura models — most commonly on Integra, RL, TL. 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. Typical repair costs on Acura range from $80 to $4,500, depending on the specific model and root cause.
Common Causes of P0304
- •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
P0304 on Acura by Model
Acura Integra(1 issue)
- Distributor internal shaft seal fails, oil leaks into cap and causes misfires + stalling1990-2001
The ignition distributor on 1990-2001 Integras (and all Honda B-series engines of the era) sits at the rear of the head and is driven directly off the exhaust cam. Inside the distributor housing, an oil seal separates the cam-driven shaft from the cap/rotor/electrical assembly above it. When this seal hardens with age and heat cycling, engine oil under pressure leaks past the shaft, fills the cap area, and coats the rotor and contacts. Result: misfires, hard starts, hesitation, stalling at idle, and sometimes a check-engine light for misfire codes. The shaft seal CAN technically be replaced internally, but it is difficult and many shops will not attempt it — they replace the whole distributor instead because reused housings often re-leak quickly. Cleaning the cap helps for a few weeks and then symptoms return.
Acura RL(1 issue)
- Distributor shaft seal leaks oil into cap, causes misfires (P0300-P0304) on 3.5L C35A1996-2004
Like every C-series V6 Honda used in the 1990s and 2000s (Legend, NSX, CL, TL, RL all share the family), the RL's 3.5L C35A V6 has a distributor mounted at the back of the head and driven directly off the camshaft. Inside the distributor housing, an oil seal isolates the cam-driven shaft from the cap/rotor/electrical assembly above. By 100,000 miles the seal hardens, oil pressure forces engine oil past the shaft, and the cap fills with oil. Result: misfires (typically P0300 random plus individual cylinder codes P0301-P0306 since this is a V6), rough idle, hesitation. RepairPal explicitly lists distributor O-rings as one of the most common Acura RL oil leak points. The figure-8 oil cooler seal and oil filter housing gasket are the other two common leaks on this engine — diagnose carefully before assuming distributor. The C35A engine remained in the first-gen RL through the entire 1996-2004 production run, so this issue affects all years.
Acura TL(1 issue)
- Oil Consumption and Fouled Spark Plugs on 3.7L V62009-2014
The 3.7L J37 V6 used in many TL SH-AWD models has a documented pattern of excessive oil consumption, sometimes leading to low oil level warnings, misfires, and spark plug fouling. Acura/Honda issued warranty extensions and service information for affected V6 engines in this family due to piston ring-related oil consumption. Owners often notice the engine using significant oil between changes, and if ignored, the condition can progress to rough running and catalyst damage risk.
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View P0304 across all makes →Frequently Asked Questions
What does P0304 mean on Acura?▼
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 Acura specifically, this code is documented across 3 models.
What causes P0304 on Acura vehicles?▼
Common causes on Acura: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0304 on a Acura?▼
Repair costs on Acura range from $80 to $4,500, depending on the specific model and root cause.
Which Acura models have P0304 documented?▼
Au7o has documented P0304 on 3 Acura models: Integra, RL, TL.