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Old 11-11-2015, 08:03 AM
Witsend Witsend is offline
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Sounds like the back of the intake valves might be coking up with carbon from the crankcase ventilation system. The ultra low viscosity oil combined with longer change intervals , means more vapors getting past the baffles and separators and drawn into the intake plenums.
With the direct injection now a days for better fuel economy, you no longer have the benefit of the cleaning capabilities of what top tier gasoline used to do to keep the backs of the intake valves clean of intake valve deposits anymore .
Any Port Cargo 08 should be able to give you an idea of suspect cylinder with most GM's. Doubt an old Counselor could be much help on some COP ignition , but on older non waste spark systems higher KV bar graph and shorter burn time on the handy bar graph were useful features to have. I remember working on motorcycles that had a miss at idle . I would do the ole spit sizzle check on the exhaust head pipes to check which pipe was running cooler. Maybe a Port Cargo infrared thermometer pointed at the exhaust manifold outlets could detect significant temperature differences better, but bet the spit check be faster.
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Last edited by Witsend; 11-11-2015 at 08:22 AM..
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