Bad Heads?

[MSR7878]

My MM has 118,000 miles and up to this point has been basically trouble free. Recently I got a check engine light and the code said "Cylinder #7 Misfire". The dealership tested the ignition and fuel systems and found both to be functioning properly. Then they performed a compression test and found #7 to be 20% depleted. My car still gets 21.5 mpg, with no smoke or anything from the exhaust. It does sound funny when warm at idle (like an air compressor). The dealership thinks it is a burnt or "spun" exhaust valve. I was wondering what you guys think, or if anyone has had similar problems.

[Larry Durham]

My MM has 118,000 miles and up to this point has been basically trouble free. Recently I got a check engine light and the code said "Cylinder #7 Misfire". The dealership tested the ignition and fuel systems and found both to be functioning properly. Then they performed a compression test and found #7 to be 20% depleted. My car still gets 21.5 mpg, with no smoke or anything from the exhaust. It does sound funny when warm at idle (like an air compressor). The dealership thinks it is a burnt or "spun" exhaust valve. I was wondering what you guys think, or if anyone has had similar problems.

I posted almost the same thing about my Lincoln ( 4.6 DOHC ) a week ago. Low compression in # 5 cyl., ruff idle, loss of power. Took it to a L/M dealer and was told internal damage, $3,000 - 5,000 to repair. NO WAY JOSE! Took it to a local garage and explalned the problem and my thoughts about a broken valve spring.They removed the valve cover and examined the exhaust valve spring and BINGO it was broken.
To make a long story short, pumped the cyl. with air, removed and replaced the spring ( which took some time and fieness ) and now runs like new.
Come to find out through some members here and on Flatratetech.com that this is a common problem with 4.6 SHOC and DHOC motors with a lot of miles. Be sure to check this first before going any deeper.
Good luck.

[MSR7878]

Thanks for the info. I will definately have a "non dealership" mechanic take a look.