Misfire
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Misfire
Ok so I have replaced several parts trying to solve missfiring. Parts are distributor cap,spacer,and rotor, plugs, plug wires and coil. I also replaced the intake gasket, carberator and set timing. This is a 1981 Ford f150 300 l6. And im still getting a missfire when you throttle it up or drive it misses pretty good. I am at my whits end and nowhere else to turn for info. If anyone can please help me solve this problem I'd be gratefull. Thanks
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From: douglasville
Do a power balance test and a compression test next,if these point to one particular cylinder and If you have stud mount rockers, one of the nuts holding the rocker arm down could be loose or could have even split in half this happens to my 300 six every few years i have to tighten the rockers up and its usually the same 3 that have worked loose. You have already tried most of what it could be.
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Did a compression test all cylinders where within 5 to 10 pnds of each other all being 140 to 150. Also checked timing chain for slack by turning crank clockwise and watching rotor. Rotor moves automaticaly so no slack there.
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From: Virginia
Can you describe it a little more? Is it a stumble when you first hit the pedal? Or is it a constant stumble only when the pedal is pushed? Does it have a miss at idle? Does it miss-fire only when the engine has a load and doesn't do it while cruising?
Does it feel like one cylinder(a minor power loss to the engine) or is it a major jerk with several cylinders involved?
Does it feel like one cylinder(a minor power loss to the engine) or is it a major jerk with several cylinders involved?
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From: douglasville
Mine also backfires when it has a loose rocker, usually through the carburetor though because its always an exhaust valve thats loose. The only other thing i can think of is if the plug wires might be mixed up somewhere
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Went off the book on firing order and Ford the nice guys they are also stamped it on the intake. And it' is through the carb on mine as well.
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Ok went ahead and removed valve cover tonight to have a look. I notice a couple rocker arms loose so I tightened them. Then I started truck to see if they all was moving as they should. One was not moving. It appears to be on the number 2 cylinder so I pulled plug wire on that cylinder. It idled ruff but backfiring through carb stopped. Any ideas why that rocker wasn't moving.
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From: douglasville
Long as the push rod looks straight its ok, the lifter is cheap and worth a try though everyone will tell you that tha cam and all the lifters have to be replaced together i have replaced just one with no issues of course you may get the side cover off and find pieces of lifter every where. If everything else looks ok then you will need a cam which is not a bad job just time consuming and you have to remove the radiator, condensor and the grille to slide it out.
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Ok I read on another post to put the push rod back in hold finger on it while cranking engine to see if it moves. It did so that' good not a flattened cam lobe. So could be dealing with a bad lifter or bent push rod.