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cylinder compression

Old 09-04-2015, 11:02 AM
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bconboy
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Default cylinder compression

I have 2005 gt with 4.6 what should the compression be in the cylinder. has a code for misfire cylinder 5, which is the same cylinder that I had to have sleeved due to a crack in the block. had the valves done on the cylinder also and the head was pressure tested.


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Old 09-05-2015, 05:15 PM
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danzcool
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It should be within about 5% of the rest of the cylinders, probably okay within up to 10%. Giving an actual number is difficult due to normal wear and tear and the compression ratio. Also, if you haven't already, you do need to allow time for the rings to seat, somewhere around 500 miles. Other than that check spark plug, coil-on-plug, and fuel injector.
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Old 09-07-2015, 10:15 AM
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bconboy
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now it is getting hot, is it possible that the valves are sticking. I am not losing coolant. I changed the thermostat and now I think it is worse. I also switched coil packs and it threw the same code, misfire cylinder 5.
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Old 09-07-2015, 02:50 PM
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YOu may need to 'burp' the coolant system after replacing the thermostat, the dealership uses a vacuum pump to get the air out of the system. I assume that since the heads were worked on that you replaced the spark plugs? Probably should check that cylinder 5 spark plug again anyway, and like I said, maybe look into the fuel injector. Have you checked your oil to make sure it is not getting coolant mixed in, would be grey and creamy if it is (which is bad).
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Old 09-07-2015, 03:03 PM
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t should be within about 5% of the rest of the cylinders, probably okay within up to 10%. Giving an actual number is difficult due to normal wear and tear and the compression ratio
True, but it will typically be between 150 - 170

Btw, if you suspect a mechanical problem a vacuum test is fast and easy and will tell you a lot about your engine.
http://www.secondchancegarage.com/public/186.cfm

good luck, hope it's something simple
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Old 09-08-2015, 02:45 PM
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the valves will not "stick".

If the block was cracked, I am surprised a shop would even try to "repair" it.
A cracked block is never good. It could easily be leaking from the cylinder again. Blowing the hot air from the cylinder into the cooling system will always make it overheat. If the crack is far enough up in the cylinder, oil will never make it into the coolant and make it milky.

Last edited by SCCAGT; 09-08-2015 at 02:51 PM.
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Old 09-08-2015, 04:19 PM
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If you are trying to determine if a cylinder is leaking, a compression test is not the best diagnostic procedure to do. A cylinder leak down test will identify any cylinder that has a problem. A leak down test uses compressed air to fill the cylinder while the valves are closed. It there is a problem with your piston, rings, valves, valve seats, head gasket or engine block, a leak down test will find it. Avoid low cost and low quality leak down testers, using a low quality tool can give you unreliable results.
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Old 09-09-2015, 07:11 AM
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bconboy
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well it ended up blowing white smoke out exhaust, so I am thinking head gasket, took all plugs out was going to check compression in all cylinders. on cylinder 5 it was full of antifreeze, same one that it was throwing mis fire code. question, before it started getting hot if you held up a piece of paper over the tail pipe it was like it was sucking the paper against it, could I have a exhaust valve sticking? and would that cause my mis fire and now coolant in the cylinder?
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Old 09-09-2015, 10:45 AM
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That's bad, real bad. With the history of your block, sounds like it took a sh*t. could be related to the head, but prob no way to tell without tearing it down.
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Old 09-09-2015, 12:15 PM
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Dino Dino Bambino
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Originally Posted by bconboy View Post
well it ended up blowing white smoke out exhaust, so I am thinking head gasket, took all plugs out was going to check compression in all cylinders. on cylinder 5 it was full of antifreeze, same one that it was throwing mis fire code.
That's bad news. At the very least you'll need to pull off the driver's side head to find out why coolant is entering the no.5 cylinder. Since it's already been sleeved, there could be a crack either in the deck of the block or in the head. Better hope it isn't the former 'cause the block would be scrap.
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