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I have read, many times, that the header crack will affect the readings of the O2 sensor. What I don't understand, is how O2 enters the headers even though they are always under pressure. At boost, the pressure in the headers may be as much as 25 or 30 psig, and air AIN'T going to leak in against that much pressure. At low or no boost, the flow of the exhaust gas is probably too low to give any venturi effect, which might otherwise suck air. Anybody know how this works?
George W
Raleigh, NC
 

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Why couldn't some air get sucked in there?
I understand that you're saying that the headers are pressurized, but it must get in there somehow. I have no meaningful explanation for you bud, I'll leave that to someone with intelligience. My honey just told me I am lacking more than my share.
 

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Simple experiment.

Take a 2liter, fill it with water and poke a whole in the top and turn the bottle upside down. The water will leak out until there is enough vacuum to hold either the water in, or make it suck air in the hole to displace the enough volume to return the bottle to equilibrium. (This is the glug-glug that you'll see if you just turn it upside-down with the cap off.)

Now if the leak stops (or comes close) poke another hole in the bottom, it'll pour out smoothly without any glug action, (and a lot quicker) you'll notice no bubble coming in the hole. Now if you force air in the second hole (ie exhaust port) no air should have to or come in the hole.

Now if for some reason there is any ever vacuum in the header (I can't think of a reason) maybe air would come in the crack. even with the crossove off the O2 shouldn't get too corrupted, think of a car running open headers they don't have erroneous O2's do they?

I'm not saying it's not possible, but I am saying I really can't justify it.



[This message has been edited by PRSRIZD_V6 (edited January 25, 2002).]
 
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