🔧 340i - Spark Plug Replacement

Spark plugs ignite the air/fuel mixture in your engine. Worn plugs can cause misfires, rough idle, poor fuel economy, and sluggish acceleration. This job is mostly about careful disassembly, keeping dirt out of the plug holes, and tightening the new plugs correctly.

Difficulty Level: Intermediate | Estimated Time: 1.0-2.0 hours

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⚠️ Safety & Precautions

• ⚠️ Work on a cool engine to avoid burns and damaged threads.
• ⚠️ Keep dirt out of the spark plug wells; debris can fall into the cylinder.
• ⚠️ Do not use anti-seize on BMW-style plated spark plugs unless the plug maker specifically says to.
• ⚠️ If you disconnect the battery, use a 10mm socket and remove the negative terminal first.

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🔧 Required Tools

You'll need the following tools for this repair:

• Safety glasses
• Nitrile gloves
• 3/8" drive ratchet
• 3/8" drive torque wrench (10–60 Nm range)
• 14mm thin-wall 12-point spark plug socket (magnetic or rubber insert)
• 3/8" drive extension set (3" and 6")
• E10 external Torx socket
• 10mm socket
• Trim clip removal tool
• Small flathead screwdriver
• Flashlight
• Compressed air blow gun
• Ignition coil puller tool (specialty)

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🔩 Required Parts

HowToo sells all the parts you need for this repair:

• Spark plug set - Qty: 1 (set of 6)
• Dielectric grease - Qty: 1

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📋 Before You Begin

• Park on level ground, shift to Park, and let the engine cool fully.
• Open the hood and remove any loose items (rags/tools) from the engine bay.
• Tip: Take a quick photo before unplugging anything.

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🔨 Step-by-Step Instructions

Follow these steps in order:

Step 1: Remove the engine cover and access panels

• Use your hands to pull the main engine cover straight up (it’s held by rubber grommets).
• If your 340i has additional covers/braces blocking access, remove them as needed:
  • Use an E10 external Torx socket or 10mm socket to remove the fasteners.

Step 2: Unplug the ignition coil connectors

• Each cylinder has an ignition coil on top of the spark plug.
• Use a small flathead screwdriver to help lift the connector lock (if tight), then unplug the connector by pulling straight back.
• Tip: Do one coil at a time to stay organized.

Step 3: Remove the ignition coils

• Use an ignition coil puller tool (specialty) to pull the coil straight up and out.
• If a coil is stubborn, gently wiggle while pulling—don’t pry hard against plastic parts.
• Set the coil aside in order (cylinder 1 to 6) so they go back where they came from.

Step 4: Clean the spark plug wells

• Use a flashlight to look down into each spark plug well (the tube the plug sits in).
• Use compressed air blow gun to blow out dirt/sand so nothing falls into the engine when the plug comes out.

Step 5: Remove the old spark plugs

• Install the 14mm thin-wall 12-point spark plug socket on a 3/8" drive extension and 3/8" drive ratchet.
• Turn counterclockwise to loosen, then spin the plug out slowly.
• Lift the plug out with the socket. Repeat for all 6 cylinders.

Step 6: Install the new spark plugs (hand-thread first)

• Check that each new plug looks undamaged and is the correct one.
• Start each plug by hand using the spark plug socket and extension only (no ratchet at first). This helps prevent cross-threading (damaging the threads in the engine).
• Once it’s threaded smoothly all the way down, switch to a 3/8" drive torque wrench and tighten.
• Torque to 23 Nm (17 ft-lbs).
• Tip: If it doesn’t thread easily, back out and restart.

Step 7: Reinstall ignition coils

• Apply a tiny smear of dielectric grease inside each coil boot (the rubber “cup” that seals on the plug). Dielectric grease helps prevent sticking and moisture issues.
• Push each coil straight down until it fully seats on the spark plug.
• Reconnect each electrical connector and make sure the lock is fully engaged.

Step 8: Reinstall covers/brace

• Reinstall any braces/covers you removed using the E10 external Torx socket or 10mm socket.
• Press the engine cover back down until it snaps into the grommets.

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✅ After Repair

• Start the engine and let it idle for 30–60 seconds. It should run smooth with no shaking.
• If you get a check engine light or rough running, shut it off and re-check that every coil connector is fully clicked in.
• Take a short test drive and confirm normal power and smooth acceleration.

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💰 DIY vs Shop Cost

Shop Cost: $350-$650 (parts + labor)

DIY Cost: $90-$180 (parts only)

You Save: $260-$470 by doing it yourself!

Shop labor rates vary but typically run $100-$150/hour. This repair takes a shop approximately 1.0-1.5 hours.

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🎯 Ready to get started?

HowToo makes it easy: same-day/2-day shipping on every part, plus all the tools and specialty tools you need! Check out the parts and tools sections below to add everything to your cart.