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#1
06-16-2008, 01:10 AM
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downstream O2 sensors
1999 7.4L
I just replaced my fuel pump & now my downstream o2 sensors are 99% of the time flatlining between 85 & 115 mV. Upstreams are fluctuating as they should between 80 & 800 mV. Any ideas? 
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#2
06-22-2008, 10:59 PM
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Re: downstream O2 sensors
Did you replace the fuel filter when you changed the pump? 9 times out of 10 the reason why the pumps fail is because of a clogged filter. If it's clogged there will be low fuel pressure giving you the lean O2 readings. There could also be a vacuum leak somewhere, or an exhaust leak sucking in outside air causing the O2 sensors to go lean.
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2000 Chevrolet Silverado Regular Cab Short Box 4.3L Vortec - 5 speed Ion Alloy 16x8" chrome wheels Magnaflow Catback Exhaust K&N Intake, Throttle Body Spacer  GM Automotive Technician Previously - 2003 Chevrolet Cavalier
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