Flex Fuel Technology / 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

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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.

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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 8th digit in the VIN denotes

the engine size and type.

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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.

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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.

Engine Block Heater

The engine block heater is a common freeze plug style heater. It is intended to pre-heat the

engine block to aid start up in very cold climates. The block heater is not always needed,

however. The operator has the option of switching to E70 or even standard unleaded fuel if

needed. So the block heater is not equipped from the factory. The block heater is to be

installed by either the dealer or other qualified repair facility as needed.

Fuel pump, tank, filter, Injectors, and lines

Since alcohol promotes corrosion, all of the parts that contact the fuel must be alcohol

compatible. This can sometimes mean they are not made from the same materials as their

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unleaded fuel counterparts. For example, the lines and filler neck on a FF vehicle are

stainless steel. Since the FF vehicle requires more fuel, some flow differences may exist as

well in the pump and injectors. Sometimes the fuel tank is larger capacity to offset the

shorter range per tank full. Naturally, any o-rings that seal the system are alcohol

compatible as well. If you are replacing any of these components be sure that you are

installing the correct part for the application. If non-flex fuel components are installed onto

a flex fuel vehicle, it is not only possible to cause damage to the component, but even the

engine as well.

PCM

The flex fuel PCM has different programming strategies when compared to a standard

gasoline vehicle.

First of all, the flex fuel PCM must be capable of distinguishing between the different types

of fuel. The Ford PCM has two different methods of achieving this, dependent on the model

year. On 2000 and prior, the PCM measured input from the flex fuel sensor to determine

this. On 2001 and later, the PCM uses a software strategy referred to as deductive refueling

logic.

Deductive refueling logic simply watches for a refuel event by monitoring the fuel level. At

the startup immediately after refueling, the PCM then looks at the O2 sensors for a slightly

different purpose than normal. At this point, it is using them to try and figure out what kind

of fuel the driver put in the tank. If the PCM is currently running unleaded fuel strategies

and suddenly sees a lean condition at that startup, it assumes E85 was added and then uses

its trim calculations to determine the amount of alcohol in the tank. After it has that amount

calculated, it then resumes its normal view of what is rich or lean in respects to the type of

fuel it thinks is in the tank. If the driver is switching from E85 back to regular unleaded, the

same is true. The only difference in the switch back to unleaded is that the PCM will now see

a rich condition upon restart after a refuel condition.

After the PCM has determined what type of fuel is in the tank, it runs new strategies

including difference base injector pulse widths and different ignition timing curves that work

with the percentage of alcohol inferred.

Diagnostics and Testing

When it comes to testing for a rich or lean condition, or the integrity of the flex fuel sensor,

you need to know how to test the content of the fuel in the tank to find the percentage of

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alcohol. To perform the fuel/alcohol test, you will need a 25ml clear graduated cylinder, a

stopper to seal the top of it, some clean water, and 20ml of fuel sampled from the fuel tank

(easiest to use the vehicles fuel pump to push it out through the pressure test port).

Refer to the fuel test illustration for these steps.

Step 1: While wearing protective gloves, fill the beaker (graduated cylinder) with 20ml of

fuel from the vehicle.

Step 2: Add enough clean water to the beaker to bring the total volume in the cylinder to

24ml.

Step 3: Seal the top of the beaker and shake it enough stir the mixture. Let it sit for 3

minutes undisturbed.

Step 4: At the end of 3 minutes, the alcohol and the water should have blended together

and settled to the bottom. The gasoline will float to the top. Record the measurement on

the side of the beaker where the water/alcohol mixture meets the gasoline.

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Step 5: Calculate the percentage of alcohol using this formula: (A-4)x5 The answer is the

percentage of alcohol in the tank. For example; If the reading on the side of the beaker is

18ml where the gas and water meet, then 18 minus 4 times 5 equals 70% alcohol (E70). If

the reading on the beaker is 10ml, then 10 minus 4 times 5 equals 30% alcohol (E30). This

test is accurate within a 10% tolerance.

Step 6: Dispose of the test fuel as contaminated fuel and wash your hands. If you have no

environmentally responsible method of disposing of the test fuel, Ford states (in their

training material) that it is OK to pour the mixture back into the tank. The added water will

be absorbed by the alcohol in the tank.

During this testing, you may notice that E85 is very weak in gasoline odor and pail in color

compared to typical gasoline. That is a normal characteristic of E85. The higher the alcohol

content, the clearer and weaker the mixture appears to the senses.

Once you know the actual percentage of alcohol in the tank, it is pretty straight forward

from here. Access the Flex Fuel Index PID on the scan tool. See if the FF index agrees with

your calculations within 10 percent. If it does, then any rich or lean codes are not a product

of the PCM using the wrong strategy. Normal diagnostics can resume as if the vehicle were

the same as a dedicated gasoline vehicle. If the flex fuel index does not match, then this

may be the cause of your rich or lean codes.

If the PCM underestimates the alcohol content, a lean condition will result (the PCM will be

commanding high fuel trims). If the PCM over estimates the alcohol content, then a rich

condition will result (the PCM will be commanding low fuel trims).

If the flex fuel index is incorrect on a system using a Flex Fuel sensor, then pinpoint testing

of the flex fuel sensor will be required, possibility ending in replacement of the flex fuel

sensor. If the flex fuel index is in correct on a system using Deductive Refueling Logic, then

clear the KAM and restart to see if the PCM relearns the correct flex fuel index. If it does,

then the problem was likely due to an improper refueling practice. Generally, this is caused

by the customer not turning the key off during refueling. It is possible however, to have a

faulty fuel level sensor cause an intermittent error in the PCMs alcohol calculation. If it again

relearns an incorrect value, then this may be caused by a vacuum leak, faulty MAF sensor,

lazy O2 sensors, or anything else that makes the PCM see or think it sees a lean condition.

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Safety Notes

I would certainly hope that telling people not to drink ethanol fuel is a given, however

Pure ethanol is indeed the same as the grain alcohol found in liquor, beer, and wine. There

is an agent, called a denaturant, added to the pure fuel ethanol before it is made into E85.

This chemical agent is intended to make the pure fuel ethanol bitter tasting. This denaturant

usually contains between 2 to 5 percent unleaded gasoline. When the denaturant is added

to the ethanol, the mixture is now called denatured ethanol. It is deadly poisonous.

The main reason for mentioning the above is to warn anyone who is taking medication for

the treatment of alcoholism such as Anabuse or some other disufiram. The vapors from E85

or even skin contact can cause the same adverse reaction as drinking beer, liquor, or wine.

In especially sensitive individuals who are on such medication, serious personal injury could

result.

For the rest of us, the same rules apply with E85 as does regular gasoline. It is explosive,

poisonous, and is a carcinogenic. Avoid the vapors, eye contact, avoid prolonged skin

contact, and do not ingest.

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