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Old 08-25-2010, 12:49 PM   #23
1996SL11.9L
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2002 SL1
Default Re: Jerky Saturn problem narrowed down to EGR valve. What next?

How can the exhaust deliberately being put in the air stream lean out the fuel mixture?

It is already a dead, spent, inert gasses. It takes place of some of the combustion air and lowers the volume of intake air with O2 in it. The fuel injection doesn't measure the amount of combustible gasses in the air stream. So it is adding fuel according to the fuel map that is skued for current operating conditions. There is a lower volume of combustable air in the cylinder then is expected and there is more fuel then avaliable O2 to burn it because some of the intake air got displaced by exhaust from the EGR. And his LTFT was -14 or whatever. It was rich and almost coding for an excessive rich condition.


Most engines under acceleration cut out / kill the EGR for performance propose. The fact that acceleration adds more volume to the exhaust stream creates more back pressure because the CAT can only flow X amount of air. That lifts the valve seat of the EGR and allows exhaust to spill over into the combustion air.

Blocking it off makes it happy. Replacing the EGR valve didn't fix it but blocking it off always does..............
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