How to Check Ford Vehicles With Flex Fuel CapabilityPosted 12/15/2004
By Jerome Hokanson
In an effort to improve air quality and lessen our dependence on imported oil, there has been a push during the past 15 to 20 years to develop and market alternative fuel systems for general transportation needs. As a result, compressed natural gas (CNG), propane, and ethanol/methanol-based fuel systems have found their way into the mainstream.
Ford Motor Co. has been producing vehicles with alternative fuel systems for the past nine years, making them available to government agencies, large corporate fleets and specialty fleets - including rental, towing, ambulance, taxi and utility companies. In most areas, the fuels are cheaper than gasoline, and there may be some tax incentives. But the main advantage is that tailpipe emissions typically are much lower.
In 1996, Ford released a 3.0L Flex Fuel Taurus, followed in 1999 by a Ranger. I have also heard reference made to 2.5L FFV Contours, and some 4.0L and 5.0L FFV Explorers, but have not talked to anyone who has actually seen one. Look for a FFV badge on the right front fender. The only visible differences under the hood are the addition of a flex fuel sensor, associated harness and plumbing, and different colored fuel injector bodies. Stickers on the gas filler door or on the calibration stickers on the doorjamb identify those that are specifically designed for ethanol or methanol.
The term "flex fuel" (FF) describes the ability of the powertrain control module (PCM) to adjust fuel control and timing to match the percentage of ethanol/methanol (alcohol) content in the fuel. Common names for these commercially available fuels are E-22 for methanol fuel and E-85, which stands for up to 85 percent ethanol. These fuels are slowly becoming available at more gas stations. The FF sensor measures the percentage of alcohol and sends a signal to the PCM. Since alcohol doesn't produce as much heat as the same amount of gas, the PCM must adjust fuel mixture and timing to ensure power output is close to that of normally fueled engines.
In general, as the percentage of methanol in the fuel mixture increases, the output frequency of the FF sensor signal will increase. For example: a fuel mixture that is 30 percent methanol has an FF sensor signal output frequency between 60 and 100 Hz, and 60 percent methanol will have an FF sensor frequency between 90 and 130 Hz. The PCM uses this frequency input to calculate the correct air/fuel ratio and spark advance for the vehicle. Regular 87 or 88-octane gasoline will read 40-60 Hz.
The sensor is mounted near the passenger-side shock tower on the Taurus and on the driver's side of the transmission cross-member on the Ranger. The sensors are fed battery voltage and ground, and produce a digital square wave signal that is monitored by the PCM. When the sensor fails, the vehicle may run very rich or very lean, depending on what kind of fuel the vehicle is running on and how the sensor fails. Loss of power or ground is somewhat common, especially if the vehicle is an off-road vehicle. A code P0176 indicates that the PCM sees the FF frequency reading as out of spec. Ford has eliminated the FF sensor on the Taurus for model years 2000 and newer, and only uses fuel trims and O2 activity to calculate alcohol content. Ford also added an FF module in the wiring harness between the gas tank unit and the gas gauge to make the gauge more accurate, but this module seems to have a high failure rate.
It's difficult to measure the amount of alcohol in a fuel sample without a graduated cylinder. Ford has a "special tool" that is just that-a small glass graduated cylinder. Fill the cylinder to the 90 percent mark with the fuel sample, and add water to the 100 percent line. Sealing the end of the cylinder, shake to mix the sample. Since water and gas won't mix and water and alcohol do mix, once the sample settles, you can determine the amount of alcohol. At the start, the mix was 90 percent gas and 10 percent water. So now if the mix is 80 percent gas and 20 percent water/alcohol mixture, that means there is 10 percent alcohol in the gas. Since the FF sensor is in line between the fuel tank and the fuel rail, it is difficult to substitute fuel to see if the sensor is reading the fuel correctly. If you can't determine alcohol content, you may be forced to drain the tank and refill with known good gas.
A good visual inspection of the FF sensor and harness will go a long way. Next, get your digital volt/ohm meter on the harness plug and compare to what the FF sensor reads on the DATA stream. Damaged sensors are somewhat common, especially in areas that have fuel quality issues. If replacing the sensor doesn't remove the code, reflash or PCM replacement may be necessary.
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