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A little while back I took my Z28 to a shop to have the U-joints replaced and while it was there I went ahead and had them change the passenger side spark plugs. Well they sent me home with a misfire on cyl 4. It wasn’t misfiring before they worked on it.
I pulled the plug on cyl 4 and the strap has a white film on it. The plug didn’t feel loose by hand but it didn’t take mucin torque to get it to break loose . So I’m not sure if it was torqued down all the way or not. A white spark plug indicates that it’s running lean correct? Maybe they damaged one of the fuel injector wires while they were
changing the plugs. However, using a mechanic’s stethoscope I can hear the injector on cylinder # clicking so I’m assuming it’s working.
While it was in the shop they took it on a “joy ride” and put 10 miles on it… I’m assuming that they may have beat on pretty hard while they had it. Hopefully they didn’t mess up someting internal but who knows. Would a bad valvetrain component cause a lean condition? When I listen with the stethoscope at the valve cover isn’t doesn’t sound any different in the cyl 4 area than the rest. I can’t hear anything knocking when I listen around the oil pan either.
If it was a vaccum leak I’d assume that I’d get a random cylinder misfire or at least a miss on more than just one cylinder. What’s next to check?
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Misfire & White Spark Plug Strap 
