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2004 - 2008 Ford F150 General discussion on the 2004 - 2008 Ford F150 truck.

Low Compression Cyl 8

 
Old 06-12-2019, 12:28 PM
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Default Low Compression Cyl 8

Morning boys,

I'm trying to help my sister who lives a couple thousand km's away... She's dealing with what she believes is a trusted shop.
Truck is a 2008 F150, 5.4l. 260,000km (160,000 miles) she's owned for about 120,000 miles. Maintenance is done mostly on time, she takes care of her stuff.

EDIT: I should also mention, truck had cam phasers done a year or so ago, it did not have the tick.

Truck had a flashing CEL. Running very rough. Showed P0304, P0308, and a few other cylinder misfires. Shop swapped coils around, miss didn't follow the coils. Replaced all 8 spark plugs, the miss went away on all cyls, EXCEPT #8. Did compression test, all very good except #8 is 50PSI. What are her next steps? What would you guys recommend, or think is wrong with the info given?

In searching other threads, they all seem to be guesses of coils and plugs, and with that ruled out, I wanted to start a new thread.

I appreciate any and all help guys, hopefully we can save her some money.

Best,
McCarthy

Last edited by McCarthy; 06-12-2019 at 12:30 PM.
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Old 06-12-2019, 12:35 PM
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Check to make sure that the plug threads arent stripped. Also, add a cap full of oil to the cylinder and redo the compression test, if it's still low then a valve seat may be leaking. If compression goes up, rings could be the issue.
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Old 06-12-2019, 01:35 PM
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Originally Posted by 650NutKase View Post
Check to make sure that the plug threads arent stripped. Also, add a cap full of oil to the cylinder and redo the compression test, if it's still low then a valve seat may be leaking. If compression goes up, rings could be the issue.
Thanks! I relayed and was told the spark plug threads were checked, and both sides appeared perfect. Waiting to hear back on the wet comp, test.

Thanks guys
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Old 06-13-2019, 12:13 AM
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They think it's a burnt valve or broken valvespring. Pulling it apart tomorrow morning.
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Old 06-13-2019, 12:54 PM
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Dang, so was it leaking down during the wet test?
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Old 06-13-2019, 04:28 PM
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Waiting to hear back. Just got a text when I posted that of what they think. Will update ASAP.
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Old 06-13-2019, 04:48 PM
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Hopefully with it being a valve, it isn't too much $$$
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