Spark plugs - I have this with photos - e mail me if you want the complete document

[Tom1999d]

24 June 2005

Changing Spark plugs on the GM 4.2L Vortec engine:

General notes: Job took 90 minutes. If I did it again I could easily do it in 45 minutes. All plugs were gapped to .050 inch. Old plugs had a .043” - .-047” due to build up on tip. Old plugs had a bit of rust where the ceramic meets the chrome plated metal hex. When I started the truck it ran rough for about 1 minute. I think this is due to loss of vacuum, and the ECU adjusting to the newer plug. I test drove the truck for about 20 miles. I realize how much power I was missing. It drives like a rocketship!

1. Remove the intake resonator. Loosen 2 SST screw clamps, remove small vacuum hose on right, remove wire from wire clip at back, remove two 10mm bolts (both on left). As you pull the black plastic resonator up remove the 3/8” hose from the underneath (connects to the valve cover – no clamp). Stuff the throat of the throttle body , vacuum barb on valve cover, & flex tube to air cleaner with a clean rag or better cover with plastic wrap / aluminum foil





2. Clean off any built up sand or dirt from around each coil. I took the opportunity to wash the black plastic resonator and check for cracks / leaks.













3. Loosen the coil hold down bolts one at a time. These are 10mm bolts. The bolts are captured to each coil assy. It isn’t necessary to unplug thee coils, just be careful not to pull out the wires. When the bolt is loose pull the coil assembly straight up.




4. Loosen the spark plug. I got all six of mine loose with out any difficulty with about 90k on the engine. Be sure the engine is dead cold. Put a dab of anti seize on the new plug threads before installing the new plug. The plastic valve cover has the torque rating in raised letters (13 inch pounds). I recommend a torque wrench to be sure you do not over tighten.






5. I did #1 (closest to front of engine) plug last. You will need to unsnap the wire way cover, and then remove the two yellow plastic tabs at the bottom of the wire way trough.

[brg1]

What spark plugs did you use for the replacement?

Did you notice a little better fuel milage?


Brian

[rickyjperez]

please send me the photo for the installation to [email protected]

[jdmccright]

The yellow tabs that hold the wire trough can be discarded and bolts used instead if you wish. The holes they press into are already threaded. Makes it easy to pull the trough aside in the future. There are three...two on top of the block and one to the right (looking at it from the front) and lower, follow the trough and you'll find it.

[rickyjperez]

i dont see the picture if you can email to [email protected]

[jdmccright]

I like Autolite platinum plugs...just regular platinum, not "double-Pt". While I can't say it was solely the plugs that helped mileage, new plugs properly gapped will help a little. But I will note I had an exhaust leak at the connection between the exhaust manifold and the downpipe. Tightening this up did help mileage back into the normal range...was 13-14 mpg, now 16-17 combined, 21-23 mpg straight hwy.