DIY: How to change spark plugs (3.0L V6)

I swapped out my spark plugs today at 50k miles. The maintenance schedule calls for new plugs at 75k miles, but it also calls for things like never changing the transmission fluid. I was also bored needed something to do. I decided to go with the Autolite XP104 plugs. Overall, the process wasn't too bad, but it is definitely time consuming. It takes a little studying to figure out how the wiring harness mounts come off the Intake Manifold and this is by far the part that will cause the most problems for anyone. Enjoy:

1. Disconnect the negative battery terminal.

2. Hoses - There are 4 hoses total that need disconnected. 3 in the back of the IM, and 1 hidden under the throttle body. Use vice grips to squeeze, unclamp, and hold the hose clamps. I didn't see the hidden one until it came time to remove the IM, this may be when you need to remove it too. The hoses push right off with minimal effort.

3. Wiring Harnesses - Ensure your battery is disconnected. Disconnect the plug on the left, and the plug on the right. On the left, use a knife to carefully cut (or crumble) the tape which holds the harness to a post on the IM. On the right, use a knife (with new blade) to carefully score a notch around the mounting tab of the black plastic, 'box-like wire guide'. Keep scoring it until this wire-guide box separates from IM. Use a flat tip screwdriver to lift the white tab and slide each harness off the IM. Don't be afraid to move these harnesses around a bit.

4. Accordian/CAI - Disconnect the MAF harness. Remove the accordian, or angled hose for the intake. Push intake to the right, into its 'hole' a bit.

5. EGR - Remove the 3, 8mm bolts from the EGR bracket. You will probably need a 8mm box wrench for the one without clearance in the back. Do not drop bolts into the engine bay.

6. Throttle Body - Lift the red tab of the harness, and disconnect. Remove (or break) the harness mount from the IM. Start with either of the bottom bolts, and remove the 4, 10mm bolts from the TB. Do not drop bolts or washers into the engine bay. It is not necessary to disconnect the coolant hose from the TB, just push the TB off to the right.

7. Intake Manifold - These bolts stay locked in the IM, they do not come out or fall out. Use an 8mm socket with extension to completely loosen all 8 bolts. Observe how easy they feel when they break inital torque. Do not use a screwdriver with an 8mm nut driver tip. Once all 8 bolts are loosened, lift up on the IM. Move the right wire-guide box out of the way, and push the EGR off to the right to clear its tube out of the IM. Keep doing this while lifting and moving the IM off to the left, until it comes out altogther. Lay it on the ground, upside down ensuring the gaskets do not become dirty. Get an old, but clean towl, and lay it over the intake ports on the engine block...this will help avoid any sudden disasters. Latch the hood and take a break.

8. Spark Plug Removal - Open and close 1 at a time, and start with the fronts to get a general feel. Remove the 8mm bolt. Carefully pull on the plug-top, remove, and let hang. Try not to let the end touch anything dirty. Use a 1/2" drive socket, with 3/8" adapter, an extension of your choice, and the 5/8" spark plug socket. Be very careful, your block is aluminum. Insert the extension into the tube and lock the spark-plug socket onto the spark plug. Put your left hand over the joint of the extension/socket, and right hand on the handle. Slowly turn the socket CCW, as soon as you feel the initial torque break, stop, then slowly continue turning until you feel the spark plug become free of the engine. Withdraw the old spark plug. Keep track of which spark plug was in which cylinder, to observe any wear problems. All 6 of mine were lightly coated with white-ish carbon, which is normal wear. The tip was shorter though.

9. Spark Plug Installation - Observe that the set gap of the new spark plug is .044 with a gauge tool. Insert a new spark plug into the spark plug socket. Put a dab of anti-seize grease on the threadings, and spread it with a paper towl and your fingers. Insert the complete socket extension with spark plug into the hole, DEAD ON STRAIGHT. SLOWLY turn the the socket CW, ensuring its dead straight to avoid cross-threading. If it cross threads, the engine is done. The new spark plug should turn so smoothly that it feels like a hot knife through butter. When you feel it beginning to torque, stop. Carefully turn the the socket in 1/16th of a turn increments until it feels sufficiently snug. If you overtorque it, the spark plug may break, deep down in that hole...and your day will be ruined. Insert the plug top, and push it until it seats with the new spark plug. Replace the 8mm bolt. Repeat 8 and 9 for the remaining cylinders.

10. Replace the Intake Manifold - Replace the IM by inserting the EGR tube into the IM. Carefully work the IM into place by lifting on its locked bolts, moving the wiring harnesses around. Connect the hidden hose first. Finger tighten the 8mm bolts on the ends, and ensure the IM is lined up. The machined bolt hole tabs on the IM should match up perfectly with the machining of the block. Tighten down the 8mm bolts in a staggering pattern. Remember how they felt when they came loose, these do not need cranked down.

11. Replace the 3 back Hoses and Wiring Harnesses. Replace the left and right harnesses to the white tabs of the IM, and reconnect.

12. Replace EGR - Replace the 8mm bolts to the EGR bracket.

13. Replace TB - Position the TB against the IM. Replace the top 10mm bolts to the TB with fingers, then replace the bottom 10mm bolts. Tighten with 10mm deep socket. Reconnect the TB wire harness, then push the red tab down.

14. Replace accordian/CAI. Reconnect the MAF harness.

15. Check over all your hoses, and wiring harnesses. Make sure everything is re-connected. Reconnect the negative battery terminal.

16. Wash your hands, start the car, and observe for any weird behavior or noise. If it starts, then immediately stalls, check your un-connected MAF. WAIT...disconnect the negative battery terminal first, reconnect the MAF, then reconnect the negative battery terminal. I almost plugged in the MAF while still powered, but I caught myself. Take it for a test drive in a safe, known area. :drive: It should feel perfectly fine. You just saved yourself a couple hundred bucks.


I haven't noticed any particular differences with the Autolite XP104, although the engine seems to have a more aggressive and perkier startup. I haven't been able to hammer on the throttle yet either though.