At my wits end, mystery issue...
01-23-2012, 11:25 AM
#24
Teching In
Join Date: Nov 2007
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Have you been driving the car much lately or just letting it sit while you work through this. It may be something simple such as a crap tank of gas at the last fill-up, vacuum leaks and/or split hoses.
Later ... Larry S.
Later ... Larry S.
01-23-2012, 12:09 PM
#25
On The Tree
I am wondering could it be a timing issue. Like maybe a cam position sensor or a timing chain jumping time. Just throwing stuff out there. I am no expert. Has a similar issue with a different car and it turned out the timing chain tensioner broke causing it to run horrible.
01-23-2012, 04:39 PM
#27
TECH Resident
Join Date: Nov 2011
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Car in question is my 2001 SS M6. I have been foolishly been throwing parts at it lately. It has a miss that I can hear and feel. However, it throws no codes - nor does it indicate a missfire when live scanned. Also, if I shut the car off for 5 minutes or less - it will not restart unless I pump the gas pedal about a 1/2 dozen times while cranking. It runs rougher than normal at idle, shakes under a load in gear - so bad that it feels like the car is comming apart. 6th gear is unuseable under 70 MPH. The car ran great up until about 4-5 weeks ago. I've done the obvious stuff, like plugs & wires. Swapped on a different set of known good coil packs to rule that out. It uses no oil, doesn't smoke, or make any funny mechanical noises. Has great oil pressure, runs cool. I am out of ideas... 
2 ways to check very easily.
use an infrared thermometer. run the engine at 2500rpm. it sounds as if it's gonna misfire there. now, let it idle, and shoot each header tube....or manifold port. the misfiring cylinders will be noticeably cooler than the rest.
other option is to pull 1 wire at a time till you hit the cylinder that doesn't change the idle.
