Cylinder #7 misfire on 5.9 magnum

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Paul Christiansen

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New york
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1998
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5.9 magnum
Hey everyone like the title says i have a cylinder #7 misfire, i changed the cap and rotor, msd street fire 8mm wires, e3 spark plugs, standard equipment fuel injector and i still have the problem. I did a head gasket test with the blue liquid tester and its fine, and i dont have blue smoke or anything out of the ordinary from the exhaust. I recently did an oil change and the oil was black, not milky so i figure my head gasket is most likely good. I then did a compression test and it turns out i have 90 psi on the #7 cylinder and i believe it was right around 175ish for all the other cylinders. Once i saw that i instantly assumed the worst and figured its a cracked head since thats apparently a common problem. I then found that we also have a plenum gasket failure problem so i guess it could be that?
SO at this point this is my plan, (the truck isnt my daily so i can afford to have it down for alittle while) i figured ill take the plenum off and take a look at the gasket, if everything looks good ill remove the head and look for cracks, and while im there look at the head gasket. (obviously im going to replace all gaskets anyway) BUT im thinking if im going to take the heads off i almost want to put on aftermarket performance heads on since im already there. If im going to have a truck with horrible gas mileage i may as well have a somewhat strong gas guzzler.

So how does my plan sound?
Where can i buy aftermarket complete heads? I googled a bunch of different things and the only real places i found was summit racing, jegs, and huges engines. At this point i cant even find parts like performance valves, springs, retainers, and rockers to bring the heads to a local machine shop to have them build it for me.
 

TMyers

USMC 84' - 92'
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The compression test would have the valves closed so the lower compression is most likely in the valve train. My bet is on a bad lifter.

Take the valve cover off of that side and watch the rockers on #7.
 
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Paul Christiansen

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Dec 14, 2018
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Location
New york
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1998
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5.9 magnum
Wow thanks for the fast response, ill look into that first thing tomorrow.

But if ends up being a lifter since i have to the the rockers off and the cam off would it just be worth it to have the head rebuilt/upgrade it? If i replace 1 lifter i imagine i should replace all 4 in the head.
 
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