Hi All, This vehicle belongs to my brother, and has me stumped. 1998 GMC K1500, 5.7L, auto trans., 85K mi.

It sets code PO305, and has a consistant misfire on cyl 5 at idle. It had 30,000 misfires in the last 300 mi. Here is a pic of the plug after 3000 mi. ... Login to read more.

Files Referenced: