2016 Hyundai Sonata Spark Plug Replacement — 2.4L GDI, NGK IZKR7B, 15 ft-lb Torque

I've done the spark plugs on a 2016 Sonata 2.4L and the job itself is clean — four coil-on-plug assemblies, top of the engine, accessible without removing anything major. The thing to know going in: this is a GDI (Gasoline Direct Injection) engine, and GDI engines accumulate carbon deposits on intake valves over time. While you're in there, I'll show you what to check and how to catch carbon buildup early.

Overview

The 2016 Hyundai Sonata's 2.4L Theta II GDI engine is standard across most trim levels (SE, Sport, Limited). Four iridium plugs with coil-on-plug (COP) ignition. Hyundai rates the plugs for 60,000-mile replacement intervals.

GDI means fuel is sprayed directly into the cylinder rather than the intake port — more efficient but means intake valves don't get washed with fuel, so carbon builds up over time.

Tools & Parts Needed

Item	Spec / Part Number
Spark plug	NGK IZKR7B (iridium)
Hyundai OEM	Hyundai 18840-10060
Alternative (budget)	Bosch FGR7DQP+
Plug gap	Pre-gapped — do not adjust
Thread size	M12 × 1.25, 26mm reach
Torque	15 ft-lb (20 Nm)
Interval	60,000 miles (iridium)
Socket size	5/8" (16mm)

Tools needed: 5/8" spark plug socket, 3" and 6" extensions, torque wrench, 10mm socket (COP bolts), compressed air, dielectric grease.

Step-by-Step Instructions

1. Cold Engine Only

Let the engine cool completely. The 2.4L GDI has aluminum cylinder heads — torquing plugs into a warm aluminum head risks stripping threads.

2. Remove Engine Cover

Plastic engine cover lifts straight off two to four locating pins. No tools needed.

3. Remove Coil-on-Plug Assemblies

Four COPs in a row on top of the valve cover. Each has an electrical connector and a single 10mm hold-down bolt. Disconnect connector, remove bolt, pull COP straight up. Move one at a time from left to right — keep track of which connector belongs to which COP.

Look down the plug tubes with a flashlight: oil pooling in a tube indicates a valve cover gasket leak.

4. Blow Out Plug Wells

Blast compressed air into each plug well before removing any plug. Any debris falling into a cylinder causes damage. Takes 10 seconds per hole.

5. Remove and Inspect Old Plugs

5/8" socket with 6" extension. Break each plug loose counterclockwise, remove by hand. Heavy black carbon on electrodes (beyond normal light tan/brown) can indicate injector or rich-running issues — note which cylinders.

6. Install New Plugs

NGK IZKR7B comes pre-gapped. Do not adjust the gap — the iridium tip is fragile and a gap tool can damage it. Thread in by hand until snug, torque to 15 ft-lb (20 Nm).

7. Reinstall COPs

Apply a thin film of dielectric grease inside each COP boot. Install each COP, press firmly until seated, snug the 10mm bolt. Reconnect all connectors. Replace engine cover.

Common Mistakes

Mixing up COP connectors during reinstall. On the 2016 Sonata 2.4L, the four COP connectors look identical. Reconnect COP #1 to COP #2's lead and the car throws a misfire code pointing to the wrong cylinder. Work one at a time left to right rather than disconnecting all four at once.

Pro Tips

• The 2.4L GDI is known for intake valve carbon buildup around 60,000–80,000 miles. Symptoms: rough idle at cold start, hesitation on acceleration. A walnut shell blasting service cleans it ($150–$300 at an independent shop).
• If your Sonata has the 2.0T turbocharged engine (Sport 2.0T), the plug spec is different: NGK LZKAR6AP11, 0.028" gap, 11 ft-lb torque.
• White-gray plug color is normal on GDI engines — don't mistake normal GDI coloring for a lean misfire.

Save Money with OwnerDrop

A dealer spark plug service on the 2.4L Sonata runs $150–$220. Four NGK IZKR7B plugs cost about $40 total. You're keeping $110–$180 in your pocket for a 45-minute job.

For more Hyundai maintenance, see the 2016 Hyundai Tucson air filter replacement guide for cabin and engine filter specs. The OwnerDrop guides library has complete service intervals for over 28 DIY procedures.

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