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1991 GMC R3500 7.4L Excessive Emissions
Posted to GM Driveability on 6/10/2011 11 Replies

Truck runs well , fails emissions at idle . With scanner installed and monitoring, perform 2500 rpm test for 30 sec ok, return to idle stays in closed loop for 15 sec then goes open . O2 sensor at .890 fixed system co goes to 2.39 and fails test . I have check...

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car Vehicle Data

1991 GMC R3500

VIN 1GTHR33N3M
Engine7.4 L / 8 cyl / GAS
Trans4-speed Automatic (Electronic)
DeliveryFuel Injection / TBI
EmissionsOBDI,CA. EMISSIONS
SymptomsExcessive Emissions
OccursIdle
Message Closed

car Vehicle Data

1991 GMC R3500

VIN 1GTHR33N3M
Engine7.4 L / 8 cyl / GAS
Trans4-speed Automatic (Electronic)
DeliveryFuel Injection / TBI
EmissionsOBDI,CA. EMISSIONS
SymptomsExcessive Emissions
OccursIdle