Flex fuel conversion (everything you need to know)

[Carl T]

What trucks run flex fuel

So there seems to be some confusion and miss conception when it comes to ethanol powered K2xx trucks so I would like to try to clear it up as well as provide a solution for those looking to convert. All 14 5.3 trucks/SUV's (along with all MY4.3's) come standard with flex fuel capability, 15+ 5.3's were optional and the 6.2 was never offered with flex option. The difference between the flex and non vehicles is the installation of a flex fuel sensor (reads ethanol content) and the ECU calibration. Since the vehicle has a sensor that measures content you can run any amount of ethanol and the ecu adjusts automatically.

 

Now that we know what has flex fuel lets discuss why it is used.

1. It has over 100 octane, that means we can run more ignition lead and make more power, that is why the L83 is rated to produce 25whp/33ft/lbs of torque on E85. With tuning you can see gains of over 30whp/40ft lbs. I have seen much higher but that is a normal number.

 

2. Stoich of E85 is around 10:1 as opposed to gasoline which is 14.7:1. That means you you need roughly 30% more fuel and will see an associated drop in economy. Because of the amount of torque produced (especially at low engine speeds) the airflow amount required to produce enough power to move the truck forward is reduced and you will get some of this back. Realisticly expect a drop of around 25-27% in fuel economy.

 

3. It is cheap, we are in the Twin Cities MN and I bough E85 for $1.44./ gallon last week. Compare that to premium fuel (all GenV engines should be ran on premium) at 2.25/gallon and you are looking at an $0.81 savings.

 

Using these numbers and assuming you drive 15k miles a year getting 17mpg average on gasoline and 11.9 on E85 (30% loss) I come up with the following.

15k miles / 17 mpg = 882.35 gallons X 2.25 = $1985.3

15k miles / 11.9 mpg = 1260.5 gallons X 1.44 = $1815.1 (Savings of $170)

 

Different areas have different pricing and this may change.

 

4. Starting operation, DI engines have extended cranks when cold starting. It is a mechanical limitation as the high pressure fuel system builds pressure to proper fuel the engine. This time is extended when using E85, as for how long maybe those who run it can comment but I would not expect more than an additional 20% cranking time.

 

What is mechanically required to run flex fuel.

Right now there are two "simple" ways to convert. We are first going to talk about what is required to physically install the system and then what is required for ECU tuning.

1. You can purchase the O.E lines for a 15 flex vehicle and install them. I found a link online and had a customer purchase all the lines, turned out they were for a different chassis vehicle and would not fit properly. I called our dealer and tried to find the proper line with no success. It sounds as if there are 3-4 different line sets depending on truck configuration. If you can find the correct line sets installation should take about 2 hours. You have to pull the driveshaft, lower the t-case and trans slightly to gain access to the upper holder to remove and install. Not sure if you can do it in the driveway as the lines need to come in at a pretty steep angle.

 

2. You can buy our complete kit, it is simple, fits all 14+ truck/SUV, installs with basic tools in 1-2 hours. You unclip the fuel line, cut 3" out of the existing fuel line, install the flex fuel sensor and included wiring harness. If you purchase the kit specific installation instructions are included that will lead you through a step by step installation.

 

3. You can fab up your own stuff, parts for everything can be had for about half of our kit. Cut your harness or install in a different location, etc.

 

ECU modification:

You can install the fuel composition sensor prior to tuning. It will not flag a check engine light or cause any performance issues. The ECU does not know to look for the input so it does nothing with it. There are two real options.

 

1. Our Custom tuning options:

A. We can mail order tune it, you send in the ecu and we bench flash it. The largest drawback to this is we are unable to do transmission tuning (the TCM is located in the valvebody)

B. Full tune: We can tune the vehicle on location, our shop is located in St Paul MN so this is more of a local item. If I can get a large group buy we can also come to your location.

C. You have access to HPtuners, you can read and send over the ECM/TCM files, we modify and send it back. You flash it in and viola! If the truck is modified we do offer remote tuning as will and will send a custom config and specific instructions on the process.

 

2. Have a tuner take care of what is needed. There are a lot of quality, established people out there that can help out if you have someone locally.

 

I hope this helps out quite a few people, I have received a lot of questions and I think this will be a quality reference point. Please feel free to submit your thoughts and personal experience.

 

I will try to add some photos later that will show the different installation options.

[Carl T]

Saved for future info

[Rawyzf]

Great post Carl.

 

I've ran 6 tanks of e85 now in my truck, and have hand caculated and posted my results on fuelly.

 

Running Premium I averaged 17.0mpg based on 43 fill ups. (16.8mpg if you use my last 10 tanks with the 33" A/T tires)

Running E85 I averaged 12.8mpg based on 6 fill ups. (I will continue to log in Fuelly and you can click and see my Sig)

 

This is about 50/50 City/Highway, with 33" All Terrain E rated 10ply Tires. So many of you will see higher numbers for both....but this will give you the general idea on the % difference. (25%).

 

As for the cranking time, I'd say it's about 25-50% longer on E85 than regular gas. The longer the truck sits, the longer the crank (this is the case for both fuels).

[joshc64311]

What trucks run flex fuel

So there seems to be some confusion and miss conception when it comes to ethanol powered K2xx trucks so I would like to try to clear it up as well as provide a solution for those looking to convert. All 14 4.3/5.3 trucks/SUV's come standard with flex fuel capability, where as the 15+ vehicles were options (not many were ordered with the option). The difference between the flex and non vehicles is the installation of a flex fuel sensor (reads ethanol content) and the ECU calibration. Since the vehicle has a sensor that measures content you can run any amount of ethanol and the ecu adjusts automatically.

 

Now that we know what has flex fuel lets discuss why it is used.

1. It has over 100 octane, that means we can run more ignition lead and make more power, that is why the L83 is rated to produce 25whp/33ft/lbs of torque on E85. With tuning you can see gains of over 30whp/40ft lbs. I have seen much higher but that is a normal number.

 

2. Stoich of E85 is around 10:1 as opposed to gasoline which is 14.7:1. That means you you need roughly 30% more fuel and will see an associated drop in economy. Because of the amount of torque produced (especially at low engine speeds) the airflow amount required to produce enough power to move the truck forward is reduced and you will get some of this back. Realisticly expect a drop of around 25-27% in fuel economy.

 

3. It is cheap, we are in the Twin Cities MN and I bough E85 for $1.44./ gallon last week. Compare that to premium fuel (all GenV engines should be ran on premium) at 2.25/gallon and you are looking at an $0.81 savings.

 

Using these numbers and assuming you drive 15k miles a year getting 17mpg average on gasoline and 11.9 on E85 (30% loss) I come up with the following.

15k miles / 17 mpg = 882.35 gallons X 2.25 = $1985.3

15k miles / 11.9 mpg = 1260.5 gallons X 1.44 = $1815.1 (Savings of $170)

 

Different areas have different pricing and this may change.

 

4. Starting operation, DI engines have extended cranks when cold starting. It is a mechanical limitation as the high pressure fuel system builds pressure to proper fuel the engine. This time is extended when using E85, as for how long maybe those who run it can comment but I would not expect more than an additional 20% cranking time.

 

What is mechanically required to run flex fuel.

Right now there are two "simple" ways to convert. We are first going to talk about what is required to physically install the system and then what is required for ECU tuning.

1. You can purchase the O.E lines for a 15 flex vehicle and install them. I found a link online and had a customer purchase all the lines, turned out they were for a different chassis vehicle and would not fit properly. I called our dealer and tried to find the proper line with no success. It sounds as if there are 3-4 different line sets depending on truck configuration. If you can find the correct line sets installation should take about 2 hours. You have to pull the driveshaft, lower the t-case and trans slightly to gain access to the upper holder to remove and install. Not sure if you can do it in the driveway as the lines need to come in at a pretty steep angle.

 

2. You can buy our complete kit, it is simple, fits all 14+ truck/SUV, installs with basic tools in 1-2 hours. You unclip the fuel line, cut 3" out of the existing fuel line, install the flex fuel sensor and included wiring harness. If you purchase the kit specific installation instructions are included that will lead you through a step by step installation.

 

3. You can fab up your own stuff, parts for everything can be had for about half of our kit. Cut your harness or install in a different location, etc.

 

ECU modification:

You can install the fuel composition sensor prior to tuning. It will not flag a check engine light or cause any performance issues. The ECU does not know to look for the input so it does nothing with it. There are two real options.

 

1. Our Custom tuning options:

A. We can mail order tune it, you send in the ecu and we bench flash it. The largest drawback to this is we are unable to do transmission tuning (the TCM is located in the valvebody)

B. Full tune: We can tune the vehicle on location, our shop is located in St Paul MN so this is more of a local item. If I can get a large group buy we can also come to your location.

C. You have access to HPtuners, you can read and send over the ECM/TCM files, we modify and send it back. You flash it in and viola! If the truck is modified we do offer remote tuning as will and will send a custom config and specific instructions on the process.

 

2. Have a tuner take care of what is needed. There are a lot of quality, established people out there that can help out if you have someone locally.

 

I hope this helps out quite a few people, I have received a lot of questions and I think this will be a quality reference point. Please feel free to submit your thoughts and personal experience.

 

I will try to add some photos later that will show the different installation options.

you sir are my hero!

[redwngr]

All 2014, 2015 and 2016 4.3L trucks are flexfuel.

 

For the 5.3L it became optional in 2015.

[Carl T]

All 2014, 2015 and 2016 4.3L trucks are flexfuel.

 

For the 5.3L it became optional in 2015.

Thanks for the input, I edited the first post.

[bigsapper]

Excellent post. The only quibble I have is E85 should be compared to E10. There are very few commercial outlets that sell straight gas anymore in Texas and I would suppose that's the case nationwide.

 

The point is the delta in your mileage is a bit less.

[gmckenzie]

 

 

Compare that to premium fuel (all GenV engines should be ran on premium) at 2.25/gallon and you are looking at an $0.81 savings.

 

curious why you say that. Thought the 5.3L was fine on regular?

[joshc64311]

whats the compression ratio 12 to 1 I think? so higher octane would yield better power/ throttle response.

[Carl T]

Excellent post. The only quibble I have is E85 should be compared to E10. There are very few commercial outlets that sell straight gas anymore in Texas and I would suppose that's the case nationwide.

 

The point is the delta in your mileage is a bit less.

 

Correct, I tried to keep it as simple as possible but the average stoich of gasoline is now closer to 14.1-14.2 instead of 14.7 due to mandatory ethanol. I don't get out much so I am not to sure if it was just us that did 10%.

 

 

curious why you say that. Thought the 5.3L was fine on regular?

 

Regular is fine, as carbon deposits build and airflow becomes slightly less consistent a little extra protection is not a bad thing. Every 87 octane L83 I have tuned has showed knock or knock learn, Ask those who data log or monitor engine data if there is a difference between reg/premium. Most on here are enthusiasts who are looking for more than "fine". I see people bring in trucks with headers/intake etc and still run regular. Regular is for Civics and Prius. Feed your truck better fuel.

 

If the trucks were not already on the edge of octane tolerance why would adding ethanol produce such a huge gain. Yes there is a chemical difference but 95% of the power increase comes from the detonation resistance of a higher octane fuel.

 

whats the compression ratio 12 to 1 I think? so higher octane would yield better power/ throttle response.

 

L83 is 11.0:1 L86 is 11.5:1, yes see comment above ;)

[Sooperdave]

Your R&D is appreciated! Good thing your not close or I would be spending money when I don't need to. But eventually I will get a tune...

[TJay74]

AS far as the E10 goes in Oklahoma almost all of the newer stations now offer Full gas and E10, most of ours have gotten rid of the E85 stuff as no one was using it here.

[crafferty]

Carl T,

Great post this should answer a lot of peoples questions. While were speaking about questions I do have one for you. What fuel lines did you guys purchase and what was the configuration they were supposed to be installed on. In my research it seems like all the trucks use the same fuel lines the only difference is the cab configuration and if the vehicle has the sensor.

 

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[Chainesaw]

Great post Carl.

 

I've ran 6 tanks of e85 now in my truck, and have hand caculated and posted my results on fuelly.

 

Running Premium I averaged 17.0mpg based on 43 fill ups. (16.8mpg if you use my last 10 tanks with the 33" A/T tires)

Running E85 I averaged 12.8mpg based on 6 fill ups. (I will continue to log in Fuelly and you can click and see my Sig)

 

This is about 50/50 City/Highway, with 33" All Terrain E rated 10ply Tires. So many of you will see higher numbers for both....but this will give you the general idea on the % difference. (25%).

 

As for the cranking time, I'd say it's about 25-50% longer on E85 than regular gas. The longer the truck sits, the longer the crank (this is the case for both fuels).

I am interested in this conversion myself.. is your truck a 5.3L or 6.2L?

[Rawyzf]

I am interested in this conversion myself.. is your truck a 5.3L or 6.2L?

I have the 5.3.

 

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