Ok this seems to be a common problem, but it just started for me today,

In whatever gear, punch the throttle, rev to 5k rpm and when you let off.... "POP" seriously loud backfire, like a gunshot...

What could be the problem and how can I fix it...

I have heard maybe it's the #4 plug, how can i tell if that's bad?

 

maybe too much fuel? does the car experience a loss of power at all??

as for checking the plug... pull the plug wire out and unscrew the spark plug (5/16" if I recall??)... it would probably be advised to change from the stock Champion plugs to NGK, Denso, or other high quality plug. In all honesty, I would change them no matter what. Things to look for on the #4 plug -- excessive carbon (black) build up, any holes in the insulator (the white part), any deforming of the ground electrode (the hook looking part) or anything else that looks out of the norm...

 

NGK IRIDIUMS!!!!!!!!!

Like I should talk Im on my fourth set of stock Champions!

 

Check the #4 plug wire as well, it's closest to the turbo and subject to the most heat, even though it's been "rerouted" on the newer models......you might want to invest $50 or so in some better plug wires (MSD), you'll get a hotter spark and they resist heat a heck of a lot better....

Dusty