Coil Pack Replacement

by Chess Martin - 25 June, 2006

You should be able to swap out a '99 Miata coil pack in about 30-45 minutes the first time with a minimum of mechanical expertise, or even inclination in my case.

Getting the right part

Not all Miata coil packs are made equal! Make sure you grab the right part when doing this swap. A coil pack from a '94 1.8 will not work with a '97 1.8, as the number of pins on each coil differ.

A coil pack can be fairly expensive (both coils, plug bracket going for $258 on Rosenthal as of August 2015 and from a local dealer close to $325). But all parts have a limited lifetime, and while a used coil pack can be swapped in to get you by, it's best to replace your dying unit with a fresh one.

First, get the tubes and wires out of your way.

  • Unhook the negative battery cable and push the brake pedal once to discharge any residual power.
  • The spark plug wires can be bit tough to pull off...I used channel-lock pliers to gently pull them off of the coil. Note the order of the wires (3,2,1,4) on the 1.6 and (4,1,2,3) on the 1.8. More information on the ordering of the wires can be found here. If you have the blue NKGs, they may be labeled with numbers.
  • The wiring harness that runs along the back of the engine connects to the CAS, and can be disconnected to move out of the way. You'll need the space to lift the coil pack out from behind the engine.
  • The wires across the top of the coil pack can be removed by pinching the underside of the plastic clips that hold them on (I used needle-nose pliers, but that only worked marginally).
  • The metal tube running from the brake booster cylinder (you'll see as it's clearly in your way) can be disconnected on the left and right ends by removing two 10mm bolts in the firewall. It may also help to disconnect the rubber tubes connected at either end.

Next, remove the coil.

  • Looking from driver's side, note the wire going from the coil pack to the engine block. This can be pulled off by squeezing the flat tab while pulling (by hand).
  • Remove the three 12mm bolts that hold the coil pack on to the rear of the engine. The top two bolts are easy to remove, and can be accessed with a box-end wrench or shallow socket. There is a third bolt on the bottom of the coil pack, dead center. Reach behind the engine to feel it, then get a wrench on it (preferably ratcheting) to remove it. If you've never taken it off before, it might be torqued down good and tight requiring a longer wrench to remove (or an extension of the stubby 12mm you have).
  • Now that the coil pack is disconnected, you should be able to maneuver it in such a way as to remove the two plugs from the rear of the coil pack.
  • You see the tabs that look like they should be pressed in? Push them fairly hard with your index finger while pulling them off with your middle finger and thumb (WATCH YOUR KNUCKLES!) (Its easier to pull the coil pack up and into the top of the engine. With the connectors on top, push the tab with a screwdriver and with another screwdriver, carefully pry upward the male connector. In fact, I find this technique of disconnecting plastic connectors with tabs a lot easier than using your hands).
  • Note that one of these wires has a blue wrap, and that the side of the coil it goes on has a blue dot...making them pretty much idiot proof.
  • Now that the old coil pack is off, note the rubber bushing on the bottom that is not on the new part. This bushing is similar to those attached to your radiator (although on a 1.8 the metal washers are glued/strong-affixed to the rubber). The heat from the rear of the engine will have also dried out the rubber. If you can remove the bushing without prying the metal from the rubber, do so. If not, and the rubber falls apart due to heat stress, you can source a new bushing from Rosenthal (part # B61P-13-363A) or via this link. (I was able to remove the bushing by loosening it with a small screwdriver. First remove the center piece. Place the flat end of the screwdriver on the edge of the bushing and carefully hit it with a hammer. You can then pry it off. Put it on the new coil pack).
  • I just put the new coil on with the two top bolts and it seems very secure. But it would be best to include the bottom bolt as well.
Put on the new coil in the logical reverse order...back wires, then bolts, then plug wires, then everything else. Hook the battery back up and take her for a spin. If it's like mine, she'll idle a bit strange for the first 10 minutes or so.

Good luck, and watch those knuckles.