You can remove the spark plugs in your 2003 Mitsubishi Eclipse by turning the spark plugs to the left. You should use a 5/8 deep well socket. The spark plugs will come out.
You have to remove the intake plenum. It just unbolts.
You have to remove the upper intake plenum.
You have to remove the intake plenum to access.
Remove plenum at front top of engine for access Coils (each cylinder has its own) sit on top of spark plugs - remove for access
remove throttle linkage, all wires to sensors, etc., there is probably a bracket on backside that you have to unbolt also. then remove all the bolts in top of plenum. lift up and out, making note if there is any vacuum hoses on the underside. you need to replace the plenum gasket before re-installing.
you must remove the plenum on top of the motor to excess the spark plugs it is not hard but time consuming to say the least
Assuming it's the V6, there are 3 in the front and 3 in the back under the plenum. the 3 in the front are really easy to get to. a good walk through on removing the plenum is here: http://home.pacbell.net/fong8/gstuff/tjc_plenum.htm
You don't remove the plenum to change spark plugs. There is no distributor, so there won't be traditional plug wire. Each plug has it's own coil (approx 2x4 inch black boxes), spaces along the top rear of the plenum. Disconnect the wiring harness from each one, then use an 8mm socket to remove the 2 bolts from each coil. Pull the coil out, and you will have access to the spark plug.
The spark plugs are located on your head for the first three, when you open your hood and you find the metaling (head) that says 24 valve V6, there are 3 plug type things on there, those are the spark plugs, the last three, are under the plenum.
Remove intake plenum, sorry, but this is a lot of work. Regards Martin
You have to remove the intake plenum air chamber to get to the 3 plugs against the firewall. It requires to buy intake plenum gaskets and go ahead and replace the PCV hose on the back of the plenum. Need to get from the dealer. Gaskets also from dealer.
If it is a v6, you need to remove the upper ontake plenum to get acess to the rear three plugs. Not fun.