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Discussion Starter #1
Another compression loss thread. Motor went from running fine to barely running during normal driving. Throwing a misfire code for #5 cylinder. I've pulled the valve cover and both valves are articulating fully and the valve springs are not broken. Ran a compression check, zero compression, no funny sounds. A rental borescope doesn't show the expected major carnage on the piston one would expect with zero compression. In the process of pulling the head now, because all the obvious things are okay. Any thought before I post results? Really stumped that this would happen with the easy life this truck leads. IF I'm lucky and I can get away with repairing/rebuilding the heads, should I do any upgrades to keep this from happening again?
 

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Pull it apart and see what you find. If pistons ok it may be a seat issue. Head mods are dependent on head year. 2003-2008 can benefit from larger valves and a port job. 2009+ are pretty much good to go factory for around 550hp setups
 

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Discussion Starter #3
Hopefully the pistons are okay. For upgrades, I'm looking for reliability over horsepower increases. I was thinking of valve springs (6.1?) that aren't prone to breaking and replacing the seats? Or are the stock 5.7 replacement parts better than the OEM 2004 stuff?
 

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Discussion Starter #5
Despite two sets of eyes, it ended up being a broken valve spring. Not sure why I didn't see it when the head was on, but it was plain as day as soon as I pulled the head off. Decided to get the heads freshened up and replace the springs. If one spring broke during just normal driving, I don't trust the other 15 springs! The piston was okay and the bores had no visible wear.
 
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