|Another of the simple DIY jobs on the Z. Either
as routine maintenance or as a performance upgrade, changing the spark
plugs is easy to do. When adding more horsepower performance mods, changing
to a 'cooler' plug can make the car run better & avoid severe damage
from running the car hard.
The service manual recommends replacing the plugs every 60k miles.
16mm spark plug socket
1. Remove the screw and bracket holding the cruise control cable to the intake balance tube.
2. Disconnect the short vacuum line connecting the passenger side fuel pressure regulator to the intake balance tube.
3. Remove the zip tie holding the wiring harness to the driver's side of the intake balance tube.
4. Remove the nuts & bolts holding the balance tube to the plenum (2 x 12mm bolts 3 x 12mm nuts) (1. & 2.), move the wire harness straps & tubing braces off the top of the balance tube flanges & 'flop' the balance tube toward the windshield. Be careful not to drop any of the three sealing O-rings into the plenum. Stuff rags into the exposed openings to keep debris from falling in the plenum (3. & 4.).
5. Unplug all of the ignition coil wires (5.).
6. Remove the coil pack holding bolts (12 x 12mm). Remove the ignition coil packs (6.). The number 6 plug (rear on driver's side) will be the hardest to work with (7.), unplug whatever wires might get in the way. On Jeff's '91 I had to unplug a few things, on Rich's '94 I didn't, some of the wiring around the plenum is different depending on the year.
7. Regap the plugs with a spark plug gapping tool. The boxes say pregapped, don't beleive it, check it to be certain. Do NOT use the cheap flat plug guages found at AutoDepot. Get one that has round wire measuring loops. They more accurately reflect the gap (it's much harder to angle them wrong since they are round). Stock gap is .044", be careful to not knock off the tiny platinum dots from the electrodes. Put a little anti seize on the threads for installation.
8. Use the spark plug socket to remove each plug & immediately replace them with new plugs to avoid debris from entering the cylinders. I have a special socket extention that will not come apart from the socket until I unlock it (8.). The plugs are a long way in there (9.) & the plug socket has a tendancy to stay on the plug until it's removed. Be very gentle when starting each plug not to cross thread. Torque plugs to 14-22 ft-lbs.
9. Re-install the ignition coil packs. I was unable to find correct torque specs for the coil pack, go with 4-8 ft-lbs (hand tight, the plenum is aluminum & will strip out easily).
10. Plug in all of the ignition coil wires.
11. Re-install the intake balance tube & get the wiring harness brackets back over the studs (5 x 12mm). Torque to 12-15 ft-lbs.
12. Reverse the remaining steps to complete.
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