Low compression #3 4.9L six
#1
10-06-2014, 05:49 PM
Join Date: May 2007
Location: Erie
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Low compression #3 4.9L six
Looking for a magic bullet here. 1980 F-150 4x4, 4sp manual trans, 4.9L 300 six has low compression on cylinder #3 & #2. Not a blown head gasket. Does fill the air cleaner with oil from crankcase pressure. Visible blow by doesn't seem too bad but clearly making enough pressure to overcome pcv vacuum. New and working PCV. no blockages in any PCV plumbing.
Here the compression numbers. Engine cold, 5300 ft elevation, throttle blocked open. Unknown miles on engine. Odometer reads 57,xxx probably at least 157,xxx. Truck had set for several years in a field. I have put about 1000 miles on the vehicle since my ownership. Engine runs surprisingly good. Starts easy. Doesn't buck or snort or backfire. Gets 15 mpg in town.
----dry wet
#1 140
#2 110 120
#3 30 60
#4 135
#5 145
#6 140
Didn't run wet test on the good cylinders. I haven't pulled the valve cover yet. Will do that tomorrow and examine for valve and valve spring issues.
I did squirt 4 shots of 50/50 mix of atf/acetone in cylinder #2 & #3 this afternoon for a soak and will redo compression test in AM.
Anybody got any idea and a fix that doesn't involve rebuilding the engine or head or both? I'm looking for a miracle fix that doesn't cost much. Your best ideas appreciated.
Here the compression numbers. Engine cold, 5300 ft elevation, throttle blocked open. Unknown miles on engine. Odometer reads 57,xxx probably at least 157,xxx. Truck had set for several years in a field. I have put about 1000 miles on the vehicle since my ownership. Engine runs surprisingly good. Starts easy. Doesn't buck or snort or backfire. Gets 15 mpg in town.
----dry wet
#1 140
#2 110 120
#3 30 60
#4 135
#5 145
#6 140
Didn't run wet test on the good cylinders. I haven't pulled the valve cover yet. Will do that tomorrow and examine for valve and valve spring issues.
I did squirt 4 shots of 50/50 mix of atf/acetone in cylinder #2 & #3 this afternoon for a soak and will redo compression test in AM.
Anybody got any idea and a fix that doesn't involve rebuilding the engine or head or both? I'm looking for a miracle fix that doesn't cost much. Your best ideas appreciated.
#2
10-07-2014, 12:16 PM
Lead Driver
#3
10-07-2014, 01:01 PM
If the mess in the air cleaner gets annoying, run the hose into a plastic bottle, like a Ketchup bottle.
I would still take off the valve cover for a look inside, but wouldn't go any father as it is just not cost effective.
Jim
#4
10-07-2014, 01:12 PM
Join Date: May 2007
Location: Erie
Posts: 24
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No difference in compression
After an overnight soak the compression results are the same. Was hoping if rings were stuck the atf/acetone might do it's magic. No luck. Clearly has compression leak into the crankcase. Am looking at diy air/oil separator/filter to put on the fresh air side of the crankcase ventilation system to keep oil out of the ac housing.
Don't have a leak down tester but am thinking about building one. Have most of the parts.
Don't have a leak down tester but am thinking about building one. Have most of the parts.
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