Engine Diagnostic Help

[pwilliamson1548]

Don't use Premium gas on a 8:1 engine. Especially with lower compression. 93 octane burns slower than 87 it causes hard starts, rough idle, gasoline blow by, and cylinder wash down. Run a tank of 87 to see if it helps. Also your Timing chain could be stretched causing the slight backfire and rough idle. That's a lot of miles for a gas engine.

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[SunlitComet]

premium and mid grade are doable in the obs vortec if the ignition map was modified for performance reasons. just wanted to put that out there. i use mid grade because of my ignition map.