I have replaced spark plugs on everything from old 2005 Toyota Camrys to brand-new 2024 Honda Civics, and after working on over 1,500 engines in Lagos and Abuja workshops, I know exactly what works and what does not in our conditions. Bad fuel from black market sellers clogs plugs fast, harmattan dust makes them misfire, and potholes shake things loose. Replacing spark plugs yourself can save you ₦25,000–₦60,000 every time, and it only takes 45–90 minutes if you follow this guide. You do not need fancy tools or a mechanic degree, just patience and clean hands. Let us get into it.
Firstly, why bother? Spark plugs ignite the fuel-air mix in your engine cylinders. When they wear out (every 30,000–100,000 km depending on the car), you get rough idling, poor acceleration, bad fuel economy, and that annoying check engine light. In Nigeria, with our adulterated petrol and endless traffic, plugs fail earlier often at 20,000–40,000 km. Doing it yourself means you control the quality and avoid mechanics who slap in fake NGK or Denso plugs.
Gather Your Tools and Parts Before You Start
You will need:
- New spark plugs, exact match for your car check the manual or online. For example, Toyota Corolla 2008–2018 uses NGK BKR5EYA-11; Honda Civic 2016+ uses Denso SXU22HCR11S. Buy genuine from Ladipo or online shops like Jumia — ₦8,000–₦15,000 per set of four).
- Spark plug socket (usually 16 mm or 5/8 inch with rubber insert to hold the plug).
- Ratchet wrench with 3/8-inch drive and extension bar (6–10 inches long).
- Torque wrench (critical — ₦15,000–₦35,000; borrow if you must).
- Anti-seize compound (small tube, ₦2,500).
- Dielectric grease (for boots, ₦3,000).
- Gap tool or feeler gauge (₦1,500).
- Rag, compressed air can, and gloves.
Park on flat ground, engine cold (wait at least two hours after driving), and disconnect the negative battery cable to avoid shocks.
Step 1: Locate the Spark Plugs
Pop the bonnet and find the engine cover, most modern cars have a plastic shield. Remove it by unscrewing or unclipping (two to four bolts usually). Underneath, you will see ignition coils or plug wires. Coils are black boxes with wires; older cars have thick rubber wires leading to each cylinder.For inline-four engines like Corolla or Civic (most common here), plugs are in a row along the top. V6 like Camry or Accord has them on both sides. Count your cylinders from the manual if unsure.
Step 2: Remove the Ignition Coils or Plug Wires
One plug at a time to avoid mixing up wires.For coil-on-plug systems (2010+ cars): Squeeze the clip on the electrical connector and pull it off gently. Then, remove the bolt holding the coil (usually 10 mm). Twist and pull the coil straight up, it might stick from rubber boot. If it does not budge, spray a little WD-40 around the base and wait five minutes.
For older wire systems: Grab the boot (not the wire) and twist-pull off. If the boot tears, replace it (₦4,000 per set).Blow out dirt around the plug hole with compressed air, you do not want sand falling into the cylinder.
Step 3: Unscrew the Old Spark Plug
Slide the spark plug socket over the plug with the extension bar attached. Turn counterclockwise slowly. If it is stuck (common with over-tightened plugs), spray penetrating oil like WD-40 into the threads and wait 10 minutes. Do not force it or you strip the threads, that is a ₦150,000 head repair.
Once loose, unscrew by hand. Pull it out and inspect: black soot means rich fuel mix (bad injectors or air filter); white ash means lean or overheating; oil means worn rings. Note the gap (distance between electrode and tip) should match your manual (0.9–1.1 mm for most.
Step 4: Prepare and Install the New Spark Plug
Check the new plug’s gap with your feeler gauge — pre-gapped ones are usually spot on, but verify. If wrong, gently bend the ground electrode (never the centre one).Apply a thin layer of anti-seize to the threads (not the electrode) it can foul. Dab dielectric grease inside the boot for easy future removal and to seal moisture.Hand-thread the new plug into the hole clockwise, finger tight only at first to avoid cross-threading. Then, use the socket to tighten to spec with your torque wrench. Torque matters: too loose and it blows out; too tight and it strips. Common specs: 18–22 Nm for aluminium heads (most cars); check your manual. For example, Toyota says 18 Nm for Corolla.
Step 5: Reinstall the Coil or Wire
Push the coil or boot back on until it clicks. Reconnect the electrical clip and tighten the bolt (8–10 Nm usually). Repeat for all plugs, do them one by one.
Step 6: Reassemble and Test
Put the engine cover back, reconnect the battery. Start the engine, it should idle smooth without misfires. Drive around the block; listen for pings or rough running. If the check engine light comes on, scan it (₦5,000 at most mechanics) might be a loose connection.
Common Mistakes I See Every Week
- Cross-threading: Always hand-start. If it binds, back out and retry.
- Over-torquing: Mechanics love impact guns, that is why plugs stick. Use torque wrench.
- Wrong plugs: Copper lasts 30,000 km; iridium 100,000 km but costs more. Do not mix types.
- Ignoring gaskets: Some plugs have crush washers, do not reuse old ones.
- Hot engine: Burns and dropped tools happen. Wait for cool-down.
In Nigeria, use iridium plugs if you can afford (₦12,000+ per set) they handle bad fuel better. Change air filter and fuel filter at the same time for best results. If your car has direct injection (newer models), plugs are harder to reach might need intake removal, so consider a pro.
Doing this every 30,000 km keeps your engine happy, saves fuel (up to 10 % better mileage), and prevents breakdowns on the expressway. I have seen engines last 400,000 km with regular plug changes. Grab your tools and try it, first time is scary, but after that, you are a pro.