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Discussion Starter · #1 ·
ok here is the deal i was going to replace the valve seals and figured just for the heck of it i would check the compression i checked cyl 4 its has 160 lbs then checked cyl 5 and it has 30 lbs i stoped there disgusted now cyl 3 has the bad valve seals it smokes for the first 3 min of start up the stops did a blow by test at the pcv valve and there was none any ideas i was thinking of trying that sea foam spray to see if it would clean it up and bring back up the compression some input please
 

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2013 F-150 XLT 4WD with 5L
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There is a huge difference between 160 and 30 lbs! All cylinders should be within 15-20 PSI of each other. With the difference you have, seals are the least of your concerns. A drop like that is either a bad/sticking valve or maybe rings. You need to dig deeper and find out before you do anything else.
 

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Discussion Starter · #4 ·
did a wet test and the compression stayed the same so i got bad valves on that cyl. im gonna try some sea foam spray in hopes that its just a carbon build up on the valve if not then i will have to take the head off
 
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