By on June 9, 2017

Ford, GM and Dodge E85 Flex Fuel Emblems. Image: Wikipedia

Longtime TTAC commentor rrhyne56 writes:

Flex Fuel. I see it more and more. From what I’ve heard, this mainly means the vehicle has a fuel system that alcohol wouldn’t eat up. (Mainly, yes. — SM)

So here’s my question: do the more recent models of these vehicles have the ability to sense what level of alcohol is in the fuel lines and adjust the engine accordingly, to make best advantage of whatever current gasoline/alcohol or alcohol/gasoline mixture is entering the engine? I watched a build on Mighty Car Mods where the Haltech engineer was tweaking just such a system.

I know, I know, I ought to just Google it. But I thought it might make for some lively discussion.

Sajeev answers:

Yes indeed, flex-fuel vehicles have a flex-fuel sensor (b.k.a. fuel composition sensor) to give such information to the engine computer. Considering the following video (wiring diagram and the “blocky” output via the scope), this older Buick’s system meets the most basic need: it triggers a switch — E85 on/E85 off. Then the computer switches between a unique fuel/spark table for whatever’s in the tank.

The only proof I see (i.e. Googled) of a system that eschews the on/off switch for a rheostat is in the aftermarket. That said, who else but the hardcore ethanol racers worry about blowing up a tuned motor from a bad batch of ethanol? Factory sensors and tunes are good enough for most, but the Zeitronix sensor gives a varying signal that interfaces with standalone fuel injection systems.

You can bet it ain’t cheap, and most folks won’t pay for all of this. So let’s get back to the current factory setup.

Replacement sensors (on older models?) are pricey, causing drivability issues and engine codes when they fail. One enterprising company is offering a defeat sensor so that an E85-ready machine returns to being a normal gas guzzler. Considering a large number of Bush-era ethanol vehicles are fully depreciated, on their last legs, etc., this defeat sensor makes financial sense.

[Image: Wikipedia (CC BY-SA 3.0)]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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53 Comments on “Piston Slap: Decomposition of the Fuel Composition Sensor?...”


  • avatar
    gtemnykh

    South Main Auto on youtube just had a video diagnosing a faulty ethanol content sensor in an ’06 Silverado. I believe a misrepresentation showing a high ethanol content was causing it to run rich (there are no ethanol stations in Western NY).

  • avatar
    chaparral

    Some automaker really oughta do an E85-native high-performance vehicle. It’s 104 octane and allows both turbocharging and high compression.

    Instead of a 2.0T with 9:1 compression making 250 horsepower on either fuel, it should be a 10:1 engine, make 300 hp on alky, and only 180 on gasoline.

    • 0 avatar
      spookiness

      I think Saab did a prototype.

      • 0 avatar
        B234R

        Saab has done (among others) a prototype that ran on E100, and did several FFVs, called biopower. The first ones in the 9-5s with saabs own trionic 7 engine control system didn’t use a separate FCS, the ethanol % was calculated after every refuelling based on how much fuel was needed for a correct mixture. I guess that is the VFCS then, back in 2004.. Others used a FCS, probably mainly because of potential issues when changing the fuel and running WOT right after and before the ethanol % has been determined. Regardless of the how the ethanol content is detected they all adjust not only the amount of fuel but also ignition and some got more power with E85 also, though that was completely artificial since they could have made the same with basically anything from E0 to E85.

        I drive a 9000 Aero that has been converted to E85 only during the summer (somewhere around 300hp/450+Nm) and in the winter a 9-5 Aero with 10:1 compression but “only” about 270hp/400Nm because it’s an automatic..
        E85 costs somewhere around 35-45% less here than E5 (30-40% less that E10) so it does make sense economically.

    • 0 avatar
      Sky_Render

      That would be a cool idea, and I know a lot of people who have tuned their performance vehicles to use E85 (more timing, more boost, more power in exchange for larger injectors and fuel pump).

      The problem is that in some parts of the country, E85 is nearly impossible to find.

    • 0 avatar
      Scoutdude

      Well Ford’s EcoBoost came from the TwinForce program and they did a number of E85 test versions and had hinted that the production model would be a FFV. Exactly because that high octane allows a very high cylinder pressure.

    • 0 avatar
      mikeg216

      Ford did a prototype with the twin force on ethanol back in the early 2000’s

      • 0 avatar
        JimZ

        IIRC it was a dual-injection setup; gasoline port injection and E85 direct injection. Ethanol has a much higher enthalpy of vaporization and would enhance the in-cylinder charge cooling.

  • avatar
    Zackman

    My 2012 Impala is a flex-fuel vehicle, but I have never used E-85.

    When I bought the car, the salesman suggested I use E-85 every 4th fill up. Don’t know if he was on the level or not.

    I don’t know if it does the car any good or harm, and there’s the physiological thing of getting less mpg, and my car, now that I no longer commute, only gets 19-20 mpg around town on gas. I’m thinking it would go down to 15 mpg, and I would have to fill up more often.

    Hey! It’s paid for…

    However, after all is said and done, I may give it a try just for kicks.

    • 0 avatar
      Sky_Render

      You’ll get 20-30% less fuel economy with E85. So unless that E85 is 20-30% cheaper than gasoline, you’re losing money by using it.

      • 0 avatar
        Scoutdude

        No it is a GM so he should see his MPG drop about 15-20% and a boost in low end torque and top end power.

        • 0 avatar
          285exp

          CAFE rating for the flex fuel Impala is 16 mpg on E85 and 22 mpg on E0, about a 27% decrease. I’m not sure why Chevrolet cars would be exempt from the laws of thermodynamics.

          • 0 avatar
            Scoutdude

            The posted numbers are simple calculations based purely on the BTU content of the fuels. However the fact that Ethanol burns at a different rate and has a much higher octane means that you can run more timing advance improving efficiency.

            Also those posted numbers are, as you pointed out based on E0, and E85 when what is found at the majority of pumps in the US is E10 and the “E85” actually varries between 70% and 85% depending on the time of the year with true 85% ethanol being relatively rare since to make a batch of that they blender needs to see predictions that the ambient temp will not drop below the mid 60’s for the next month or two.

            Add it all together and the average is that you should expect a 15-20% drop in MPG “E85” vs the usually found E10 with a Ford or GM FFV. A Chrysler product on the other hand will likely see a much more significant drop since they make it happen by just allowing a larger amount of long term fuel trim rather than actually learning the fuel and properly adjusting the timing curve to optimize power and economy.

          • 0 avatar
            285exp

            I don’t know you got the idea that the CAFE rating for E85 was based on simply reducing the E0 rating by 27%, maybe you can show us? It’s my understanding that they have to go through the standard dyno testing. I know that they adjust the EPA E85 rating by a set percentage so it does not negatively effect the overall CAFE rating, and actually it artificially increases the mpg rating for CAFE purposes. Any real world test I’ve seen confirms the approximate 30% loss in mileage, see Car and Driver and Consumer Reports testing.

            Simply advancing the timing isn’t going to optimize a flex fuel engine for E85, in order to take advantage of the higher octane they’d need to greatly increase the compression ratio. You can reduce the fuel efficiency loss to less than the expected 27-30% if you design the engine to burn E85, but running E85 in an engine that also has to be able to burn much lower octane E0 is going to cost you very close to the proportional loss of energy content. If the E85 is actually E70, that doesn’t make Chevrolet able to lose only 15-20% on E85, the additional 15% ethanol would be worth another 5% hit versus E0.In the real world, almost all the fuel available is E10, so the E85 real world hit is really about 3% less than it would be vs E0.

    • 0 avatar

      It would be interesting to see what the “seat-of the pants” dyno differences were.

  • avatar
    salmonmigration

    Shouldn’t the knock and O2 sensors be able of adjusting timing and fuel input? Why is a fuel quality sensor even necessary?

    • 0 avatar
      MBella

      This is what most modern flex-fuel systems use. The fuel composition sensor has been eliminated from most systems because of the high cost of the sensor. The composition sensor is a bit quicker, verses without it.

  • avatar
    TR4

    Does anyone actually use E85 on a regular basis? Around here it’s usually 10-20% cheaper than regular, but the vehicle is expected to use about 27% more so the result is a cost increase.
    My understanding is that the reason flex fuel vehicles are out there is that the auto makers get to grossly inflate the fleet fuel economy for CAFE purposes. Something about assuming E85 is used 50% of the time, but only accounting for the gasoline used.

    • 0 avatar
      stingray65

      Last information I have seen is the E85 has no more than 2% share of gasoline based fuel sales in the US. It is truly just a boondoggle program to get support from corn farmers, Archer Daniels Midland, and the automakers (who get a break on CAFE). Best evidence suggest biofuels are a total waste environmentally.

      • 0 avatar
        gtemnykh

        I think it is absolutely 100% correlated with Iowa’s timing of their primaries and it being a huge corn producing state. No one wants to come out and say it’s an absolutely insane waste of money and resources. Until some very clever genetic engineering occurs to make cellulosic based ethanol (and not just going after what’s in the ear), I just can’t see pursuing corn as an ethanol source. Trying to copy Brazil’s effective sugar-cane ethanol model directly over to a vastly different crop is nothing short of stupid.

    • 0 avatar
      FerrariLaFerrariFace

      My father-in-law does in his Expedition. I’ve tried to convince him that he’s not saving any money, but it falls on deaf ears. He also struggles to operate a smartphone.

    • 0 avatar
      redapple

      YOU ARE CORRECT SIR!
      IT’S ABSOLUTE CRAP

    • 0 avatar
      chaparral

      Yes. My ’99 Civic Si requires 93 octane gasoline. When I refuel, I use 3 gallons of E85 and 7 gallons of 87 octane E10, resulting in a 93-octane E30 fuel.

      Its price per gallon is about $2.30 versus $3.30 for 93 octane gasoline, and based on the fuel trims in my engine computer I burn about 10% more of it than E10 gas.

      • 0 avatar
        PrincipalDan

        @chaparral, so you actually stop part way through fueling. Shutdown the pump. Reinsert your card, select a different grade of fuel, and finish fueling up?

        Do you also get out of the shower to pee? /s

        • 0 avatar
          chaparral

          PrincipalDan,

          Yes. It adds about thirty seconds to refueling and I save $5 or so.

          I also notice a couple of percent of extra power when towing uphill; with two karts and a toolbox any grade hurts with only 97 cubic inches.

          No comment on your second question.

          • 0 avatar
            PrincipalDan

            Which is why I used the sarcasm tag.

            I was in Albuquerque and noticed there was a VP Racing Fuels store there. True racing fuel was around $9 a gallon.

          • 0 avatar
            JimZ

            “I also notice a couple of percent of extra power”

            LOL.

            *Sure* you do.

      • 0 avatar
        mik101

        B16A2 (160hp) in the 99 Si is 10.2:1 and requires 91 octane with the USDM/CDM ECU. PR3 is the designation stamped on everything, just like the OBD0 JDM B16A engines.

        JDM B16A (170ps) were 10.4:1 and called for 93 octane with the JDM and other foreign market ecus running a slightly different fueling and timing maps. P30 is the designation stamped on all of the parts for those engines.

        I have a Del Sol vtec (formerly B16A2 engined) and built have built multiple JDM B16A Civics (OBD1/OBD2) for myself and others.

    • 0 avatar
      Scoutdude

      I don’t use it regularly since it really isn’t available in my area but I did experiment with it extensively in a FFV Taurus on trips to areas where it can be found. You will never see a 27% drop from most vehicles and even less on a Ford or GM FFV than some others. See my other comments for more information.

      The thing is that the relationship of MPG to E% is not linear and in fact depending on the vehicle between 40-50% can obtain as high as mpg as the vehicle gets on E0 with a bonus of added power. At that level the BTU content is down, but not that much while the octane is up significantly allowing more timing and more efficient combustion. I tried that a number of times and could exceed the mpg obtained on the only other fuel available E10. Now that was on Ford’s 2nd gen FFV system that still used a physical FCS. Haven’t tried it in my E150 FFV but if I did I’d be sure to pay attention to the cautions about refueling a VFCS vehicle I outlined below.

    • 0 avatar
      SirRaoulDuke

      If I rent a Flex-Fuel car I fill it for turn-in on E85. Damn straight I will save a couple of bucks then lol.

  • avatar
    redapple

    When I use E 0 I get 28 MPG.
    When I use E10 I get 26 MPG.

    So, when I go from E0 to E10, I get a 7% decrease in MPG.
    Well then, why not just leave it out of gas altogether?????
    Evil crap.
    Thanks ADM.

    • 0 avatar
      PrincipalDan

      What really grinds my gears is that the automakers get a little CAFE credit for building E85 vehicles even if that vehicle NEVER sees a drop of E85 in its tank. As you mentioned if someone actually uses E85 they get LOWER fuel economy while the automaker laughs all the way to the bank.

      • 0 avatar
        redmondjp

        Dan, it’s not just the automakers that are laughing about E85. Consider the fact that our gasoline is taxed by volume and not by energy content. So the federal and state governments are also laughing all the way to the bank when you use E85.

        • 0 avatar
          Scoutdude

          Not the federal gov’t because it is not taxed purely on volume of fuel, there is credit based on E% so they get less tax on E10 than they do on E0 and even less on the E74 that is the most common blend of E85. States on the other hand usually just tax it all the same.

    • 0 avatar
      bullnuke

      Oh, noooooos! Don’t leave ethanol out of fuel. I say this as I view the green stalks of ethanol now emerging from vast fields around me backgrounded by a large stack emitting steam from the natural gas heating of the ethanol stew in a plant nestled between giant hoppers full of dried ethanol from last years crop. The effect on the Cadillac Escalade and GMC Denali dealers in Dayton and the RV dealers in Richmond would be catastrophic. A couple of the larger ethanol growers would be (gasp!) forced to start actually rotating crops again. Please! Remember the little people! It’s for their children!

    • 0 avatar
      Sky_Render

      I’ve got a ’14 Fusion with the 2.0 Ecoboost. I run exclusively 93 octane E10, because it’s all I can get around here. I get around 36 MPG steady state at 65 mph.

      I once found a station while on a trip that sold 100% pure gasoline 93 octane. I filled up with that and got 40 MPG in the same conditions.

  • avatar
    sco

    Was in Wisconsin last week where the Kwik Trip chain of convenience stores is a major gas outlet. They sell unleaded 87 octane/10% ethanol and then something they call “unleaded 88” which is 88 octane and a few cents cheaper per gallon. Its also 15% ethanol (in the fine print). So in the case of Kwik Trip, the marketing strategy for E85 is to confuse and mislead the customer into buying it.

    • 0 avatar
      brn

      Kwik Trip is one of the most reputable companies I’ve ever dealt with. Your assumptions about their intent are incorrect.

      I’m also not sure how your story encourages people to buy E85. E15 maybe, but not E85.

      • 0 avatar
        tankinbeans

        Kwik Trip, at least in Minnesota, has been replacing, or reconfiguring, all of their pumps where Unleaded 88 (with up 15% ethanol) replaces unleaded plus. I believe unleaded plus used to have a cited octane rating of 89 and now Unleaded 88 cites and octane rating of 88. Generally speaking the Unleaded 88 is a few cents cheaper, and is the grade advertised on tge price board, because of its increased ethanol content. All of the stations I’ve seen provide E0 91 octane.

        There’s signage for each grade. Unleaded 88 is supposedly only authorized for vehicles made after 2001, I think. Regular unleaded can go into evrything. They try to scare you saying 91 should only be used in small engines and vehicles that can be registered as collectors.

  • avatar
    smallblock

    I think some of the newer vehicles are flex fuel without using the ethanol content sensor. I can’t find a link right now, I think it used something like the vapor pressure in the tank instead along with the wideband vs. pulse width to detect it, or somethinkg like that. Either way I don’t think newer FFV’s have the sensor in the return line anymore.

  • avatar
    RS

    They should be making Biobutanol instead of ethanol.

    • 0 avatar
      28-Cars-Later

      Please expand on this.

      • 0 avatar
        PrincipalDan

        https://en.wikipedia.org/wiki/Butanol_fuel

        That’s all I could find. I’ve never heard of Butanol before now.

      • 0 avatar
        RS

        http://www.biobutanol.com/

        …Another advantage is that biobutanol has a higher energy content than ethanol, almost 20% more by density. Due to its similarities to conventional gasoline, it is able to blend much better than ethanol with gasoline. It has even shown promise when using 100% biobutanol in a conventional gasoline engine. Besides these, biobutanol experiences a lower chance of separation and corrosion than ethanol. Biobutanol also resists water absorption, allowing it to be transported in pipes and carriers used by gasoline. A very exciting advantage of biobutanol is that vehicles require no modifications to use it.

        It’s available in Houston, TX right now according to this article.
        http://www.greencarcongress.com/2016/11/20161112-gevo.html

        http://www.greencarcongress.com/biobutanol/

  • avatar
    Scoutdude

    Sorry Sajeev but you’ve got a lot wrong.

    When Ford, GM and The automaker formerly known as Chrysler started working on Flex Fuel Vehicles they all used a fuel composition sensor (FCS) to detect the percentage of Ethanol or Methanol in the fuel. It is not a switch as shown in the one video they send a signal that varies in direct proportion to the alcohol content. If they did a simple switch it could be way off when you fill a less than empty tank with winter blend E85 and in most areas it would always detect at least a little ethanol now a days.

    With GM and Ford not only is the injector pulse width adjusted so is the timing. However again it is not an A or B thing. It is closer to an FCS% x (B-A) + A, where the actual timing commanded is somewhere between the values in the two tables and proportional to the Alcohol Content.

    However even for the mfgs the FCS was an added cost that was not insignificant. So they switched to the VFCS or Virtual Fuel Composition Sensor as they figured out that they have the technology to infer the E% since in the mean time Methanol had lost the war and disappeared.

    So how do they do it now? By using the other sensors already required on the vehicle. As most people know the computer stores a ton of information for multiple reasons. For testing the EVAP system the computer has to know the level of fuel in the tank, how long since the engine last ran, intake and coolant temps. So it can figure out when it has been refueled and knows more or less how much was in the tank and added. Since it also knows and remembers the temp it can also make an Educated guess on what the actual E% is being added, whether it is more likely to have Full summer blend E85, winter blend which is really E70 or the transition blend.

    So here is what happens once you turn the key on a modern FFV. Before you can get to crank the computer takes readings from all of its sensors. If there is enough difference in the fuel level reading between the last shut down and the engine is up to temp it will start the fuel learn mode.

    Once it enters fuel learn mode it does a rough calculation based on current learned E% and the possibility of what could have been put in the tank. It then uses that best guess in fueling calculations. Monitoring the O2 sensor it then makes the corrections necessary to get closer to the true E%. Once it thinks it is in the ball park on fuel then it learns the timing. Again it uses a E0 and an E85 timing look up table and uses the current inferred E% to scale between the two extremes. Next it will play with that timing while monitoring the knock sensor to check how close it is to the optimum timing. If necessary it will adjust and infer its own idea about the E%. Then it will compare the calculation based on timing to the calculation based on fueling. Once that goes back and forth a few times the computer will declare the fuel “learned”, use that in the fueling and timing algorithms, and wait for the next refueling event.

    If you look at the right scan tool you can see this happen in real time if you look at the “fuel learned” and inferred E% PIDs.

    Because Ford and GM use adaptive timing they tend to have a much lower drop in MPG when operated on E85 vs those other mfgs who have just allowed for a larger range of acceptable long term fuel trims.

    Now for those of you with a flex fuel vehicle, particularly if it is a GM you need to be careful with your refueling event. Never ever leave the ignition on while you are fueling, you’ll mess up the computer’s triggering of fuel learn mode. Also don’t fuel on ground that is too far off level, ie keep all 4 wheels on the concrete pad if there is a ramp leading up to it. Fill your vehicle after it has reached operating temp, particularly in cold weather. Once you restart the vehicle drive it for at least 5 minutes. Don’t fuel up at the pump, drive 20′ to the parking in front of the store, shut the vehicle off and go in for snacks or to take a leak. Otherwise the vehicle can get its calcs way off causing things like off idle stumbles, general miss fires and reduced fuel economy. For GM there is a TSB noting that the first step in diagnosing driveablity concerns on FFVs that lack codes is to check the inferred E% and do a rationality check, including taking and testing a sample of the fuel in the tank. If the learned and tested E% are too far off then the solution is to manually reset the learned E% value to match what was tested in the tank. Then provide the customer with the above refueling cautions. Additionally stick to one grade as switching back and forth between various octanes can also mess up the computer’s calculations.

  • avatar

    Maybe it’s Christian Koenigsegg, but someone invented a flexfuel system that works with a infrared spectrometer that tells the ECU the precise composition of the fuel, allowing engines to run on any combination of alcohols and napthas. I think GM originally used a capacitive sensor while Ford usedoptical sensors based on the refractive indices of the fuels.

    • 0 avatar
      Scoutdude

      Ford used capacitive sensors on the E85 vehicles. But they found out that they had enough other information to learn the fuel very accurately w/o a sensor.


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