Flex Fuel Technology

By Glen Beanard technical contributor

What is Flex Fuel?

Flex Fuel can be defined as a vehicles ability to run on different mixtures of alcohol fuel. A flex fuel vehicle has had modifications made to it at the factory to allow it to operate on such a mixture. These modifications are not only hardware differences in the fuel system, but also software differences in the PCM.

Gasohol?

The alcohol of choice to use in this blended fuel is Ethanol. Ethanol is made from distilling sugar cane, fermented corn and other such agricultural goods. You may have seen gas pumps that say E85 on the sides of them. The E stands for Ethanol and the 85 is the percentage of ethanol in the mixture (85% ethanol and 15% gasoline), E100 of course being pure ethanol.

You might be a familiar with the term Gasohol. E85 is not really Gasohol, technically speaking. Yes, the idea is similar, but the mixture makes the difference. Gasohol was name given to some E10 to E15 fuels in the early 80s. In gasohol, the primary ingredient was gasoline, and alcohol was the additive. However in E85, gasoline is now the additive. So technically, it is not really gasoline, and it is not gasohol. It is an alcohol fuel with a gasoline additive. Just a piece of trivia for your customers if you get on the subject with them.

There is another type of alcohol that can be used in such a blend. That other alcohol type is Methanol. Methanol is derived from wood and paper waste products. That blend, of course, being M85. Much of this discussion can be applied to M85, however no auto maker currently supports its usage. So this discussion will be centered on E85.

A glance over chart #1 reveals information as to why E85 may be the choice fuel over M85.

Also, Ford Flex Fuel systems will be used for technical reference. Much of this technical data can be applied to other makes, but may not be identical. Be sure to consult your technical resources before servicing any flex fuel vehicle.

The Pro and Cons

Alcohols are more corrosive than gasoline. This is because they are electronically conductive and may cause corrosive impurities. Alcohol also attracts moisture which also increases its tendency to promote corrosion.

Cold weather can pose an obstacle to E85 because ethanol does not vaporize as quickly as unleaded gasoline. For the warmer regions, this may be a non-issue because E85 will have sufficient vaporization for temperatures down to 10 F (-12 C). If the vehicle operator wishes to use an alcohol fuel below 10 F, the operator should switch to E70 and/or add block heaters. E70 has a 30% unleaded fuel content. The added unleaded fuel in E70 produces more vapors in cold weather than E85.

A major difference between gasoline and alcohol is that alcohol has no hydrocarbon atoms in it like gasoline does. Instead, it has oxygen atoms. The added oxygen atoms bring pros and cons to the combustion chamber. As a plus, the added oxygen helps support combustion. This means less air is needed, plus the burn is cleaner since there are fewer hydrocarbons in the combustion chamber. On the down side, the extra oxygen waters down the air/fuel mixture with more oxygen. So, to counter act that, the fuel mixture must be richened to a 9.8:1 ratio on E85. A 9.8:1 ratio is approximately 30% richer than a normal combustion mixture of 14.7:1 with regular gasoline.

Another characteristic of alcohol is that each atom has less heat energy than gasoline atoms. However, since there are more of them in that 9.8:1 ratio, there is more power generated per firing event. The 30% richer mixture far offsets the potential 3% to 5% power increase, though. Overall, this still results in a lower fuel economy. The price of the fuel is slightly lower per gallon, but more is consumed. Therefore, operator economy is not a benefit of E85. Benefits of E85 come from less toxic emissions, cleaner engine, less national dependency on foreign resources, and benefit to the economy of domestic agriculture.

Identifying A Ford Flex Fuel Vehicle

Important: This subtopic pertains only to Ford vehicles. You will have to review information sources for other makes.

Many Ford flex fuel vehicles have an emblem found on the front fenders that resembles a roadway with a green leaf hanging over it (see picture #1). However, most of the newer models no longer use that emblem.

Even if they dont have the green leaf on the fender, they will have another label inside the fuel door. That states Ethanol Fuel or Unleaded Gasoline Only. However, in the event of a crash, it is possible that emblems may be forgotten to be reinstalled. Therefore it is important for you to be able to use other methods to identify these vehicles.

The VIN number is one of the best methods. As you know, the 8^th digit in the VIN denotes the engine size and type.

Taurus/Sable: 93 to 98 VIN digit 1 is a Methanol/Gasoline FFV. No Methanol vehicles were built after 98. 97 to 05 VIN 2 is an Ethanol/Gasoline FFV. Take note that in the years 97 and 98 E85 and M85 vehicles were both built. The alcohol types between these two vehicles are not interchangeable. VIN 1 is Methanol/Gasoline only, and VIN 2 is Ethanol/Gasoline only. There is no Methanol/Ethanol/Gasoline application.

Ranger: 99 to 2005 & , VIN digit V is an Ethanol/Gasoline 3.0L OHV FFV.

Explorer/Mountaineer: VIN digit K is an Ethanol/Gasoline 4.0L SOHC FFV.

The calibration code found in the door jam can also identify a flex fuel vehicle. If it has a prefix of 610 C, then it an ethanol vehicle. If it has a prefix of 610 G, then it is a methanol vehicle.

Flex fuel vehicles will also often have a special sticker added to the inside of the fuel door that states what types of alcohol the vehicle is compatible with. Take note that, at this time, there are no four cylinder or eight cylinder flex fuel Ford vehicles. It is important to note that the 3.0L Duratec DOHC engine found in newer Taurus and Sable uses a VIN digit 1, however, it is not an FFV. In addition, the 4.2L in the F-series and E-series vehicle uses a VIN digit 2, however it is not a FFV. Z is used on 6.8L Expedition CNG and 5.4L F-series CNG vehicles, this also not to be confused with flex fuel.

Flex Fuel Theory and Operation

Flex Fuel Sensor

On all Ford Flex Fuel models up to and including 2000, Ford used a flex fuel sensor. The flex fuel sensor mounts in the high pressure fuel line in the engine compartment. It measures the fuel conductivity, temperature, and its dielectric constant (the ratio of the amount of electrical energy stored in an insulator) to determine the alcohol content in the fuel. The flex fuel sensor (FF sensor) sends a duty cycle to the PCM.

.

The frequency of that signal increases as the alcohol content increases (see chart#2). On 99 and prior Taurus, a fuel mixer was also used. A fuel mixer is a devise that the fuel must pass through to ensure accurate readings from the sensor. The fuel mixer has the outward appearance of a fuel filter, and mounted in the fuel line directly before the flex fuel sensor. Although it appears similar to a filter, inside it is just a dead ended porous tube.