351w misfire
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351w misfire
got a 84 f 250 351w ho. It has a 260 comp cam. New coil, distributor, cap , rotor , plugs , wires and a new Holley 650 cab secondary. Runs ok, the spark plugs are white ish like its lean. Also has a new Intake. I can't find any vac leaks. It only has a misfire at idle after the truck is warm. Other than that it runs great.
Lead Driver
Joined: Nov 2013
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How consistent is the misfire? How about a quick cylinder balance test of pulling spark plug wires to disable one cylinder at a time?
If the RPM doesn't drop with a particular plug wire removed, that would point to something specific to that cylinder such as a bad plug wire, collapsed lifter, etc.
If the RPM drops a fairly consistent amount for each cylinder, that would point to a broader problem such as the idle mixture, vacuum leak, etc.
If the RPM doesn't drop with a particular plug wire removed, that would point to something specific to that cylinder such as a bad plug wire, collapsed lifter, etc.
If the RPM drops a fairly consistent amount for each cylinder, that would point to a broader problem such as the idle mixture, vacuum leak, etc.
FTE Legend
Joined: Nov 2015
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From: Angier, NC
got a 84 f 250 351w ho. It has a 260 comp cam. New coil, distributor, cap , rotor , plugs , wires and a new Holley 650 cab secondary. Runs ok, the spark plugs are white ish like its lean. Also has a new Intake. I can't find any vac leaks. It only has a misfire at idle after the truck is warm. Other than that it runs great.
I have found on 1 motor if the motor runs too lean it can hurt the plugs and it will never fire right.
Have you tried turning the idle mix screws out to see what it does for idle?
That will have nothing to do with the plug color for driving RPM so I would go up 2 jet sizes as a start.
Yes could also be a bad lifter but I have seen a lot of motors have a little misfire at idle and still run good.
Dave ----
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