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Low compression


Blown1
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Galant VR-4 org Post #: 1050664 posted 02/08/12 02:09 PM     Remind Me!  Send Private Message   Edit Post      
This may be a silly question but would lower compression in one cylinder cause a richer or leaner condition and why?


Edited by Blown1 (02/08/12 02:09 PM)

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Justin
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Galant VR-4 org Post #: 1050711 posted 02/08/12 08:07 PM     Remind Me!  Send Private Message   Edit Post      
Wohoo! Good question! This depends on how bad the compression was.

Extreme case:

The one cylinder has compression that is so bad that it isn't firing anymore. You (hypothetically, not actually), being the dumbass that you are, are still driving this thing. Oh, and you are still feeding that cylinder with fuel, because the injector is still plugged in. None of this fuel is being burned, which means the majority of it is being pushed into the exhaust. The O2 sensor sees this, and thinks that the car is running rich, and the ecu responds by leaning everthing out.

So the actual situation is that it goes rich out of the tail pipe, until the computer corrects for it, and then the remaining cylinders go lean.

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fivesfe
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Galant VR-4 org Post #: 1050734 posted 02/08/12 09:28 PM     Remind Me!  Send Private Message   Edit Post      
Good question. Out of curiosity why is it being asked?

Do you have a cylinder with low compression and your are trying to tune?

or is it that your running rich/lean and your paranoid?

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Blown1
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Galant VR-4 org Post #: 1050818 posted 02/09/12 07:47 AM     Remind Me!  Send Private Message   Edit Post      
ECU + logger and wideband giving different tales and I'm paranoid . And no I would not drive my car if it was that way its still withing the service limit but needs a rebuild anyways. I have a fully built 2.0 waiting to go in but need to get some more funds. I was just curious lol....

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Wizardawd
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Galant VR-4 org Post #: 1050958 posted 02/09/12 08:05 PM     Remind Me!  Send Private Message   Edit Post      
Do both a dry and wet comp test. Post the numbers. If they all shoot up a lot with a wet test, rings are getting worn. If they only go up a tad and still have that one cylinder a little weak, its probably the valves not seating as tight as they used to. Which you may be able to help with a little combustion chamber conditioner.

Wiz



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Blown1
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Galant VR-4 org Post #: 1051041 posted 02/10/12 06:38 AM     Remind Me!  Send Private Message   Edit Post      
Ok thanks bro will do....

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grocery_getter
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Galant VR-4 org Post #: 1051074 posted 02/10/12 11:29 AM     Remind Me!  Send Private Message   Edit Post      
Quoting galant1517:

Wohoo! Good question! This depends on how bad the compression was.

Extreme case:

The one cylinder has compression that is so bad that it isn't firing anymore. You (hypothetically, not actually), being the dumbass that you are, are still driving this thing. Oh, and you are still feeding that cylinder with fuel, because the injector is still plugged in. None of this fuel is being burned, which means the majority of it is being pushed into the exhaust. The O2 sensor sees this, and thinks that the car is running rich, and the ecu responds by leaning everthing out.

So the actual situation is that it goes rich out of the tail pipe, until the computer corrects for it, and then the remaining cylinders go lean.





If the fuel is not burned completely or only partially burned, then the air is also not burned completely or only partially burned which will increase the O2 content in the exhaust stream. It will flag the O2 sensor to read lean and cause the ecu to give more fuel. O2 sensor doesn't sense fuel, it senses O2 (air).

Same scenario why a missfire always reads lean.



Andre
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Justin
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Galant VR-4 org Post #: 1051091 posted 02/10/12 01:19 PM     Remind Me!  Send Private Message   Edit Post      
Yes. Someone finally called my bluff.

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DR1665
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Galant VR-4 org Post #: 1051106 posted 02/10/12 02:36 PM     Remind Me!  Send Private Message   Edit Post   
Sidecar: Isn't there also a chance that dumping fuel into a dead cylider would wash the walls, contaminate/breakdown the oil, and potentially lead to spun bearings?

/curious



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