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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: bigchevyc30 on June 29, 2011, 02:09:50 pm
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ok i have a 1980 c-30 with a 366 big block in it sometimes when i shut it off the truck will still keep turning itself over and over like some diesels today it did it for like 30 seconds when i shut it off what could be causing this or has anyone else had this problem
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Really advanced timing would cause that.
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I'd check your idle speed as well...
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advanced timing--retard timing (after checking).
hot spark plugs--get cooler set.
Vacuum leak--check for leaks.
remedy can be using a higher octane, but, that is just covering the problem up.
Can also turn engine off in Drive, then, once off, switch to park.
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i thought shutting the motor off in drive was bad for it and it did this with the old motor also i have heavy duty platinum plugs in the truck also for my spark plugs they are different from what i had in the old motor which still did it to. ive checked and my truck has no vacuum leaks.
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It can also occur from carbon deposits in the heads or on top of the pistons....
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I don't know all the possible reasons, but I've seen it a few times from people turning up the idle speed stop screw to compensate for vacuum leaks.