carbon monoxide reading it to high

15

Asked by Oct 04, 2011 at 04:25 PM about the Ford Bronco

Question type: Maintenance & Repair

how can i reduce my carbon monoxide reading. i am at 91.00 and should be 55.00. i have adjusted the air/fuel mixture and it only brought it down to 91. any tips would be appreciated.

4 Answers

replace the oxygen sensors.

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2,735

How did you adjust the air fuel mixture? Is the engine carbureted?? Assuming it is a fuel injected system, as the other responder did, I'll continue on that premise: Oxygen Sensors are a good suggestion for starters. If you do this, make sure you change the upstream sensors, not the downstreams (if equipped). On an OBD-II system, the upstream sensors should be mixture control while the downstreams are for emissions and the ECU compares the reading between the two sensors as a means of measuring the catalytic converter's efficiency and to verify its proper operation. High CO is caused by a rich fuel mixture. Though one or more old and poorly functioning Oxygen Sensor(s) could certainly be a potential cause for this, there are other possibilities as well. If you have access to a scantool that can linkup with your Bronco's ECU, it would be useful to get baseline readings from several of the sensors and compare them to known-correct values. Though I believe the last Bronco's were manufactured before OBD-2 was mandated and I believe they run Ford's OBD-1 system, known as EEC-4. Does your vehicle have a proper idle? Oftentimes when I come across a rich fuel mixture in an EEC-4 system, long before the system will ever turn the engine light on, it will have difficulty maintaining a smooth idle. A rich mixture is typically indicated by a low and/or surging idle, hesitation upon throttle opening, and when revved once, the engine will dip to a lower rpm than normal idle and then rebound up once or twice back to the correct idle speed. It goes without saying to make sure the engine is in a good state of tune, as in good spark plugs gapped properly, good spark plug wires, a clean air filter, and a clean MAF sensor element (if it is a MAF system). If possible, test Throttle Position Sensor voltage with a digital voltmeter. Base idle voltage should *probably* be ~0.98v, with a smooth sweep up to a maximum of ~4.5v. Check ignition timing as well if adjustment is possible. Ignition timing that is retarded relative to stock recommendations will be a problem. Note that it MAY help to remove the battery cables for approximately 15-30 minutes, while turning the light switch on and putting the key into the "On" position and back off again. This will hopefully ensure that the ECU's memory is erased. The goal in doing this is to erase the existing adaptive fuel trim tables, which may be skewed rich, and to allow the ECU to create a fresh set of tables from baseline. The vehicle will likely need to be driven a few miles (NOT aggressively!) to bring it back to proper operation.

15

sorry for the lack of info. it is carburated. 5.8L 1984. i changed the O2 sensor. i installed new cats. thanks for your replies.

15

O2 sensor have been replaced

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