Question about 1991 Oldsmobile Cutlass Supreme
My car had a bad miss and ran like **** I was told to change the coil packs and module. I did that and it still has a bad miss and bad fumes coming from tail pipe. Could it be a bad O2 sensor?
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Posted on Jan 02, 2017
Are there any fault codes in the ECM? No "Check Engine" light on?
Black smoke means it is running rich. You should be getting Rich O2 sensor codes. Running rich is usually caused by the Mass Airflow Sensor. (MAF) This is located in the snorkel that connects the air filter to the throttle body. Make sure that the snorkel hose is properly connected to the sensor housing as well as the throttle body housing. (See Picture)
Also be sure to check the reference voltage (VREF) to the MAF, MAP and TP sensors. It should be right at 4.8 to 5.2 volts. If it is low, suspect a shorted sensor. Note that several sensors are served by the same VREF circuit. I had one GM 3.1L engine that was running like **** and smoking black that had only 2 volts at the MAF. I started unplugging sensors to see if the VREF would come up to specs and found that I had 5 volts at the MAF with the Coolant Level sensor (in the radiator tank) unplugged. Replacing the Coolant Level sensor fixed the car. Any of the sensors could cause the same problem if it is shorting the VREF circuit.
If the VREF circuit checks out OK, Then I would Try a MAF sensor
If you are getting misfire codes, you probably have an injector sticking open.
Posted on Oct 11, 2009
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