DH Words and Stuff

Spark Plugs Replacement

23 Apr 2020
  • Vehicle: 2012 Mazda 3i, 2.0L, vin G
  • Tools Used:
    • 15mm box wrench
    • 8mm box wrench
    • Socket wrench with 10” extension (3” won’t be enough)
    • 5/8” spark plug socket
  • Parts Purchased:

100k+ miles, a rough idle, sputtering engine starts, and a negative fuel trim meant it was time bid adieu to the old plugs. I should have replaced them at the recommended 75k miles, but I was too busy not being busy.

Spark Plug Info

NGK replaced the ILTR5A-13G with ILTR5K13 (90607) for Ford/Lincoln/Mercury vehicles and LTR5BI-13 (90083) for Mazda vehicles.

NGK LTR5BI-13 Specs

  • Torque Spec: 7.2 - 14.5 lb. ft. against aluminum
  • Longevity: 100k miles
  • Gap: Pregapped to 0.05”

Procedure

  1. Wait for the engine to cool down unless you’re a firebender or don’t mind some sick burns.

  2. Pop off the plastic engine cover. If you’ve never done this, just pull up from the back of the cover with your hands. Do not eat the cover.

  3. Use a 15mm wrench to remove the two plastic engine cover holders. remove engine cover holders

  4. Disconnect the wire going to the first plug, and use a 8mm wrench to remove the screw holding the ignition coil in place. remove ignition coil screw

  5. Gently remove the ignition coil (these are expensive!) and take care to prevent debris from falling into the spark plug hole unless you’re helping an annoying neighbor. remove ignition coil

  6. Remove the spark plug using a socket wrench with extension and spark plug socket. An over-torqued plug is stuff of nightmares, so if you have one, pray it doesn’t destroy the threads on the cylinder head. remove spark plug

  7. Nothing to do in this step except to check out this 100k+ miles spark plug. remove spark plug

  8. Add a thin coating of di-electric grease to the ceramic portion of the new spark plug, and another thin layer to the inside of the rubber opening on the ignition coil. Tip: use a Q… tip. Be sure to not grease the spark plug electrode or the electrode contact inside the ignition coil. Di-electric grease is not non-conductive.

  9. This one’s a freebie. According to NGK, their spark plug threads have a special coating that do not require any anti-seize. Don’t be a fool and over-torque your plugs because you anti-seized the crap out of them.

  10. Another freebie. Don’t gap the spark plug. Iridium plugs are delicate, and plus, these are already pregapped to 0.05”. This is within the service manual’s spec of 0.049” - 0.053”.

  11. Screw the spark plug back into the cylinder head. Do NOT over-tighten. If you’re cool, tighten with a torque wrench to 7.2 to 14.5 foot pounds. If not, NGK’s own website says:

    If a torque wrench is unavailable, finger tighten the spark plug, then use a plug wrench to tighten. 1/2-2/3 turn on plugs with a gasket. 1/12-1/8 turn on plugs with a tapered seat.

  12. Screw the ignition coil back into place and reconnect the wire.

  13. Repeat for the other 3 plugs.

Results

  • Reduced hesitance during start up
  • Smoother idling
  • Short-term and long-term fuel trims within healthy range

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