Asked in Cadillac DeVille
How do you change the spark plugs and wires on a 1999 Cadillac DeVille?
Northstar engines are very difficult to work on. Recommend taking to a trained professional.
If you are adventurous, remove the plating on top the engine (with the Cadillac emblem; should be 2-4 bolts). If the spark plugs are not visible, then you may have to remove the secondary plate (2-4 bolts as well). On later model Northstar engines (after model year 2000) the distributorless ignition system was changed to a-on-plug design; each head has its own ignition module.
Once again, if you are not entirely comfortable removing obstructions until you reach the spark plugs, take your vehicle to a prefessional.
It's not a very arduous task. I just did one myself.
Take off the plastic cover by removing the 4 plastic bolts.
If possible, take a picture with a camera or cell phone for future re-assembly.
Remove the metal cross-brace...4 (13mm) bolts and set aside. (less than five minutes).
Unplug the wires from the spark-plugs.
Unplug the four connectors from the coil assembly on the rear valve cover.
Using a 10mm socket with 3 inch extension, remove the four bolts holding the coil assembly. 2 in the front are easy and 2 in the back just a little more tedious. (good time to look at the assembly).