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  #16  
Old 08-10-2014, 11:18 AM
alloro alloro is offline
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Originally Posted by 03GRS View Post
Hi Alloro...I was told that if there was a bad vacuum, PCV valve, etc that the PCM would lean out the engine, causing the misfires.
Vacuum leak misfires are old school predating engine computers as we know them today. In today's world with a vacuum leak the computer can compensate to a point by enriching the mixture. OTOH misfires allow excess fuel into the exhaust, in turn the O2 sensors see less oxygen and figure the system is running rich, so the computer leans out the mixture, hence the P0174 code.
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Old 08-18-2014, 04:34 PM
pdqford pdqford is offline
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Originally Posted by alloro View Post
OTOH misfires allow excess fuel into the exhaust, in turn the O2 sensors see less oxygen
Actually, the misfire causes the oxygen to not be consumed, and therefore the O2 sensor sees too much oxygen and tries to compensate by adding more fuel.

You want to check the freeze frame data to see if the engine was under load when the code set. If it was , check the fuel filter and the fuel pump pressure. Inadequate fuel supply can cause a lean misfire and/or the lean code. Additionally the freeze frame will show the fuel trims so you can see if the PCM was trying to compensate, and if it was compensating on one or both banks.

If the engine was unloaded look for a vacuum leak.
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Old 08-18-2014, 08:18 PM
alloro alloro is offline
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Actually, the misfire causes the oxygen to not be consumed, and therefore the O2 sensor sees too much oxygen and tries to compensate by adding more fuel.
Might want to double check that bud.
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Old 08-19-2014, 12:01 AM
pdqford pdqford is offline
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Might want to double check that bud.
alloro, I tried the PM thing but it said you are not accepting PMs.

See page 9 of this document. It explains better than I can what happens to O2 content of exhaust gasses when a misfire occurs.

http://www.autoshop101.com/forms/h56.pdf
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Old 08-19-2014, 10:01 AM
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r2millers r2millers is offline
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Quote:
Originally Posted by pdqford View Post
alloro, I tried the PM thing but it said you are not accepting PMs.

See page 9 of this document. It explains better than I can what happens to O2 content of exhaust gasses when a misfire occurs.

http://www.autoshop101.com/forms/h56.pdf
Very good info. Thx for sharing.
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Old 08-19-2014, 10:01 AM
 
 
 
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