I have to give a big thank to every one gave an advise in this topic, specially lhassebrock.
Actually, I have find one coil not working and I am going to change it tonight.
Is it normal for these coils to go bad, or there must be a reason that I have to search for before just changing the coil. any more advices?
is there a big difference between the Original and the after market ones?
BTW the installed is Delphi.
GM Lover,BanditGTP and Machoman I will go next to check the catalytic converter. what are the symptoms that it is clogged? as I hope the back fire will end after changing the coil, I hope so.
Appreciate all your help