Loss of compression on one cylinder...help?
01-03-2003, 04:53 PM
#1
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Loss of compression on one cylinder...help?
from front to back
192
188
178
92
when a cap of oil was added to the last cylinder, it came up to 125.
Is a leakdown the only way to find out what the culprit is? The oil looks good & the car doesn't smoke at ALL, so does that rule out a head gasket?
car is apr stage 3 (18K, 18months on the kit, 46K on the car, chipped at 5K).
When intake is pressurized, you can hear hissing at the oil cap & won't pressurize past 5psi(crankcase?) Think valves? Will a leakdown make it conclusive?
yes, I'm really pissed. Car has seen about 4 track days, never dragged, regular Mobil 1 0w40, good gas, mostly commuting miles.
192
188
178
92
when a cap of oil was added to the last cylinder, it came up to 125.
Is a leakdown the only way to find out what the culprit is? The oil looks good & the car doesn't smoke at ALL, so does that rule out a head gasket?
car is apr stage 3 (18K, 18months on the kit, 46K on the car, chipped at 5K).
When intake is pressurized, you can hear hissing at the oil cap & won't pressurize past 5psi(crankcase?) Think valves? Will a leakdown make it conclusive?
yes, I'm really pissed. Car has seen about 4 track days, never dragged, regular Mobil 1 0w40, good gas, mostly commuting miles.
01-03-2003, 05:15 PM
#2
yeah do a leak down on that cylinder. At least if you hear hissing at the intake,
or exhaust pipe you'll know it's the valves not closing or seating properly. Anywhere else requires a teardown.
Try flushing the oil and maybe use a different grade - like 5w-30 or 10w-40 just to see if there is just a stuck lifter that will come back to life.
Try flushing the oil and maybe use a different grade - like 5w-30 or 10w-40 just to see if there is just a stuck lifter that will come back to life.
01-03-2003, 08:23 PM
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Is the low cylinder #4?
You might also want to check your intake track to see if there is oil in it. When I lost the rings on 2 of my cylinders I had tons of blow by and oil all the way up near the TB and the TB hose was soaked.
01-04-2003, 01:58 AM
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Steve,I assume the numbers are in order and it goes cylinder #1 to #4. Do you notice how each gets
lower numbers? Did you start with #1 and check each cylinder in order or is that the test order? Because it looks like the battery was becoming weaker with each test and not letting the starter spin the engine as fast with each test. Which would result in lower test numbers as the engine speed slowed.When doing a test you should hook the battery to a powerful charger or another car to eliminate this possibility. As it stands your numbers may be scewed quit a bit.
When you added oil(wet test)the numbers will always increase(unless you have 0 blow-by/perfect ring seal). A increase of that much would point to a piston/ring sealing issue but because of the proggressive decline from cylinder #1 to #4(if that is the order you listed or you listed the test order),I'd rerun the test with some way of keeping the battery fully charged through the whole test( make sure the TB plate is wide open.)
If you do a leak-down test,you will need the tester($60.00 and up) and a constant scource of compressed air (usually 90 psi or greater.)You will need to get each cylinder at TDC of the compression stroke (bumping the engine with the starter will not cut it) and have a way to secure it(keep it from turning when the air is added,which can be violent.)
Once this is done and you perform the test (with the TB plate open and the intake hose off,radiator tank cap off,and oil cap off)this will tell you where the loss is at. Air rushing out the exhaust indicates a exhaust valve/valve seat problem. Air out the TB indicates a intake valve /valve seat problem. Air bubbles in the coolant tank or a rise in coolant indicates a headgasket/cracked head issue. Air out of the oil cap MAY indicate a ring/piston sealing issue depending on the % differential between the pressure added to the cylinder vs. what the cylindar will hold(that's why a leak-down tester has two gauges.)
But I'd re-run the compression test first ,like I said ,before you get upset.
When you added oil(wet test)the numbers will always increase(unless you have 0 blow-by/perfect ring seal). A increase of that much would point to a piston/ring sealing issue but because of the proggressive decline from cylinder #1 to #4(if that is the order you listed or you listed the test order),I'd rerun the test with some way of keeping the battery fully charged through the whole test( make sure the TB plate is wide open.)
If you do a leak-down test,you will need the tester($60.00 and up) and a constant scource of compressed air (usually 90 psi or greater.)You will need to get each cylinder at TDC of the compression stroke (bumping the engine with the starter will not cut it) and have a way to secure it(keep it from turning when the air is added,which can be violent.)
Once this is done and you perform the test (with the TB plate open and the intake hose off,radiator tank cap off,and oil cap off)this will tell you where the loss is at. Air rushing out the exhaust indicates a exhaust valve/valve seat problem. Air out the TB indicates a intake valve /valve seat problem. Air bubbles in the coolant tank or a rise in coolant indicates a headgasket/cracked head issue. Air out of the oil cap MAY indicate a ring/piston sealing issue depending on the % differential between the pressure added to the cylinder vs. what the cylindar will hold(that's why a leak-down tester has two gauges.)
But I'd re-run the compression test first ,like I said ,before you get upset.