E85 FlexFuel engines - what is the difference?

"BadMotorScooter" (badmotorscooter) 02/13/2015 at 11:55 • Filed to: None

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Right, I know that a FlexFuel engine is designed to burn up to 85% ethanol and 15% gasoline mixture, but what exactly is different between a modern FlexFuel capable engine and the same engine that is not E85 compatible?

My household recently acquired a new 2015 GMC Yukon with the 5.3 liter V8. This is a recent build, with some production updates that were applied mid model year. One of the changes was the deletion of E85 capability on the 5.3 V8. Earlier builds of the 2015 5.3 were E85 compatible. Now, I'm wondering what exactly makes this later version not compatible, but earlier builds of the same exact engine were compatible.

I suspect that the engines are, in fact, the same and that E85 compatibility has more to go with CAFE weighting and overall flexfuel applications across the fleet. In the Sierra and Silverado trucks, E85 compatibility is a$100 option on the 5.3 V8 - otherwise it is the same engine. I bet that $100 buys you the yellow filler cap, and not much else. All modern fuel systems use ethanol compatible materials, and an engine that has an E85 version available has E85 sized and compatible injectors as well as fuel maps.

Here in the midwest, E85 is sometimes available for as much as 50% less than gasoline. Overall MPG on E85 is usually around 30% less than unleaded (E85 has about 30% less BTU energy per unit than 100% gasoline), but it can still be economical. However, because ethanol has a very high octane rating, it can be used in very high compression spark-ignition engines which would make them much more efficient than a standard compression gasoline engine (like a diesel). FlexFuel engines are compromise because they have to tolerate 87 octane unleaded and don't have the high compression to extract efficiency from E85 fuel. A variable compression engine would solve this problem, and let us get more power and MPG from E85 when available, versus gasoline. If E85 is cheaper, then it's even better.

HammerheadFistpunch > BadMotorScooter 02/13/2015 at 12:00

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Different fuel lines and pumps and...well..basically anything the fuel touches that could corrode is replaced with hardened materials (Alcohol is corrosive to traditional fuel lines). its actually a great deal to buy a flex fuel because the price difference is small and the increased durability of the equipment is more than worth it, in my opinion.

HammerheadFistpunch > BadMotorScooter 02/13/2015 at 12:02

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Also, don't buy that 30% less economy biz, in reality its 40-50%

spanfucker retire bitch > BadMotorScooter 02/13/2015 at 12:03

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The biggest thing is the fuel lines. Ethanol will eat the shit out of anything that's only designed for conventional hydrocarbon fuel.

Unless the car says it's E85 compatible, don't fill it with E85.

Will with a W8 races an E30 > HammerheadFistpunch 02/13/2015 at 12:04

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Yup, just slightly different materials. Ethanol resistance, just like anything else, falls on a spectrum. A part that can handle 15% ethanol for 20yrs/200,000 miles may only survive E85 for 10 years.

I wouldn't be surprised if they also downsized the injectors a bit - big injectors (like those needed for ethanol near WOT) tend to have issues metering out very small amounts of fuel accurately (like with gas at idle).

DoYouEvenShift > BadMotorScooter 02/13/2015 at 12:07

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On gasoline the L83 makes 355 horsepower and 383 pound feet of torque, but if you run it on E85 and you'll be rewarded with 380 horsepower and a whopping 416 pound feet of torque.

BadMotorScooter > HammerheadFistpunch 02/13/2015 at 12:26

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Right but in the L83 5.3 V8 from GM, they have the same engine that is both E85 compatible and not (two versions of the same engine). I don't think there are any material or design differences between the two versions. GM does not make two different fuel pumps, lines, injectors, etc. The materials and parts are the same. The only difference appears to be the fuel cap color and the official E85 rating.

Maybe fuel maps are different, but even that seems like a stretch.

HammerheadFistpunch > BadMotorScooter 02/13/2015 at 12:30

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Who told you GM doesn't have different fuel lines and pumps? they do.

BadMotorScooter > DoYouEvenShift 02/13/2015 at 12:33

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I've heard that but never seen published numbers, is that confirmed from GM?

DoYouEvenShift > BadMotorScooter 02/13/2015 at 12:49

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As far as I know. Ive read it on multiple sources.

ntl0505 > BadMotorScooter 02/13/2015 at 13:04

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Pics. I'm curious. I thought all new 5.3s were ffv.

BadMotorScooter > HammerheadFistpunch 02/13/2015 at 13:33

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For the same L83 engine? Same engine code, one version (a $100 option) is E85 compatible and the other is not. The fuel pump and lines and injectors are the same part number (I believe).

RallyWrench > BadMotorScooter 02/13/2015 at 13:43

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I know the older ones used a fuel quality sensor (alcohol sensor as mentioned below) to detect the change & were possibly more complex, but my information via Alldata & a couple of different vendors only show 1 pump for 2014 5.3s, part number 19259393. The fuel maps will be much different to compensate for the much different energy density between fuels, but it switches automatically. I don't actually work on these things though, so don't have much expertise on them beyond that. Here's the rest of the E85 info for a 2014 5.3 from Alldata:

E85 Flex Fuel Description

E85 compatible vehicles no longer use an alcohol sensor to determine and adjust for the alcohol content of the fuel in the tank. Instead, the vehicle calculates the alcohol content of the fuel through measured adjustments.

The ethanol calculation occurs with the engine running after a refueling event has been detected via a measured change in the fuel level sender output. The virtual flex fuel sensor (V-FFS) algorithm temporarily closes the canister purge valve for a few seconds and monitors information from the closed loop fuel trim system to calculate the ethanol content. This logic executes several times until the ethanol calculation is deemed to be stable. This may take several minutes under low fuel flow conditions such as idle, or a shorter time during higher fuel flow, off-idle conditions.

Air-fuel ratios and the corresponding ethanol percentage are updated following each purge-off sequence. The fuel alcohol content percentage value can be read on a scan tool.

When an E85 compatible vehicle is built, an ECM or PCM replaced, or if the learned alcohol content has been reset with a scan tool the fuel system will need to contain ASTM gasoline with 10 percent or less ethanol content.

A minimum of 11 liters (3 gallons) must be put in the tank in order for the vehicle to recognize a re-fueling event. It is not necessary to turn the ignition OFF in order to have the re-fueling event recognized, however local safety regulations should be followed.

After the re-fueling event, the system registers the amount of fuel that was added, relative to the amount that was in the tank. Reading fuel trim and O2 sensor activity, the system determines if the fuel added was either ASTM Gasoline or ASTM E85. Based on that determination, the system adjusts to the expected alcohol mix in the fuel tank , and then the fuel trim and O2 sensor activity fine tunes the adjustments. The system must remain in closed loop in order for this adjustment to occur. Numerous short trips after switching from gasoline to E85, or E85 to gasoline, can result in driveability symptoms due to the inability of the system to adjust for fuel composition by not attaining closed loop operation.

Switching Between Gasoline and E85

No special precautions need to be taken when switching back and forth between gasoline and E85 other than re-fueling events must be 11 liters (3 gallons) or greater, and the vehicle must remain in closed loop long enough, usually by the time the engine has maintained full operating temperature, to calculate the composition of the new blend in the tank.

BadMotorScooter > ntl0505 02/13/2015 at 14:06

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Right, I don't think there is any real difference. i think the FF compatibility has more to do with fleet credits and how CAFE measures a FF vehicle.

ntl0505 > BadMotorScooter 02/13/2015 at 15:05

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I'm curious to see some proof though. I can't find anything about new 5.3s NOT having e85 capability.

BadMotorScooter > ntl0505 02/13/2015 at 16:29

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I know the 2015 Yukon we have is not E85 capable. The manual simply says if the if the filler cap is yellow then it is E85, if not then it isn't. Also, for the pickup truck, the 5.3 is E85 capable for a $100 option, otherwise it isn't. I just don't think there is any functional difference between the two, and would bet that the non-FFV would run E85 just fine.