DIY flex fuel?

Engine in question is an LQ9 6.0L with ported LS6 heads and 11.3:1 CR. 95% street, 5% HPDE.  Cam is 234/240 with 113 LSA.  I'll be using 55lb injectors so there should be plenty of headroom for extra fueling.

I'm planning on running pump gas in it and 500hp will be plenty for me, but looking toward the future I think ethanol will become more plentiful.  Right now it is only at about 1 in 10 gas stations in my area, and I don't plan on moving to Wisconsin just for E85.

I could build it and run 93, then someday down the line convert to ethanol, but the thought popped in my head... flex fuel so I have the option of either?  I'm not really that well versed in the way OEMs do it other than a fuel sensor and magic happens in the ECM to fuel and timing curves.  Is it something that I can add with relative simplicity, or is it something too complex to really accomplish.

The fuel sensor has largely gone away as exhaust sensing has gotten better.  I can't remember the last flex fuel car we did with a sensor- all that really needs to be done is open up the learning window for some distance after a fill up.  The system will set a baseline of how much ethanol is in there, fix that value, and then let the system learn from there.  Until the next fill up.  It's really easy with WB sensors.

What ECU will you be using?

MadScientistMatt said:

What ECU will you be using?

Do you have a recommendation?? 

There are definitely versions of the OE computers that do flex fuel but the implementation depends on the version. Early ones were with the sensor, the later ones just using fuel trims.

In reply to Curtis :

This may be a stupid question but why couldn't you grab a flex fuel ECM from a junkyard car and use that switching sensors to be compatible ?  

Let GM handle the flex fuel part for you? A lot of the full size GM trucks and SUVs that I see have flex fuel badges. It seems like using an ECU from one of those would be a good start? It should already be mostly compatible with your LS, and it has the flex fuel capability built in. I don't think you'd even have to touch the flex fuel parts of the software as long as your hardware is the same as the GM trucks (Not sure if they use a flex fuel sensor or not, but Ford phased those out around the turn of the century, so it might just be O2 sensors).

You'd just have to tweak fuel/timing for your mods like any other non-flex fuel tune, and make sure you've got enough injector to handle the increased volume of E85.

frenchyd said:

In reply to Curtis :

This may be a stupid question but why couldn't you grab a flex fuel ECM from a junkyard car and use that switching sensors to be compatible ?  

Why in the world would you buy it used when you can get them brand new???

Or better yet, set your system to not even need one.

alfadriver said:

The fuel sensor has largely gone away as exhaust sensing has gotten better.  I can't remember the last flex fuel car we did with a sensor- all that really needs to be done is open up the learning window for some distance after a fill up.  The system will set a baseline of how much ethanol is in there, fix that value, and then let the system learn from there.  Until the next fill up.  It's really easy with WB sensors.

Interesting! Did not know.

MadScientistMatt said:

What ECU will you be using?

I have the one that came with the LQ9, but I'll have to swap it out with a different OEM choice.  The engine I have was drive-by-wire so it lacks the IAC driver (it's integrated with the electric throttle body).  I will need to find an OEM ECM with that driver since I'll be doing a cable.

My initial thought was to find a flex fuel ECM but wondered if that was a few simple sensors or if it was like cobbling together a junkyard stability control and expecting it to work well in a completely different vehicle.

It won't be quite that bad, but your limit to cable drive is likely one of the earlier ECU that uses the sensor vs the newer ones that use fuel trim. Unfortunately I can't think of somewhere (good) to get specifics other than calling HP tuners and asking them.

Paul_VR6 said:

MadScientistMatt said:

What ECU will you be using?

Do you have a recommendation?? 

There are definitely versions of the OE computers that do flex fuel but the implementation depends on the version. Early ones were with the sensor, the later ones just using fuel trims.

That is my primary question... If it's a fuel sensor and an ECM, that's easy.  If it's a combination of seven sensors, three unicorns and affected by moon phase, that's different.  I realize it isn't an overly complex concept... it just needs to know the concentration of ethanol and have the proper maps to alter the fuel and spark curves accordingly, but we also know in the land of modern emissions and the million-dollar R&D, sometimes OEMs make a simple function into a complex level of algorithms that might make it prohibitive to retrofit into an engine swap.

frenchyd said:

In reply to Curtis :

This may be a stupid question but why couldn't you grab a flex fuel ECM from a junkyard car and use that switching sensors to be compatible ?  

My thought exactly... unless GM made it overly complicated and difficult to retrofit.

STM317 said:

Let GM handle the flex fuel part for you? A lot of the full size GM trucks and SUVs that I see have flex fuel badges. It seems like using an ECU from one of those would be a good start? It should already be mostly compatible with your LS, and it has the flex fuel capability built in. I don't think you'd even have to touch the flex fuel parts of the software as long as your hardware is the same as the GM trucks (Not sure if they use a flex fuel sensor or not, but Ford phased those out around the turn of the century, so it might just be O2 sensors).

You'd just have to tweak fuel/timing for your mods like any other non-flex fuel tune, and make sure you've got enough injector to handle the increased volume of E85.

On gasoline, I should need about 40 lb injectors at an 80% duty cycle.  Ethanol should be around 50 lb.  I have 55 lb, so I should be covered... until I switch to all E85 at which point it will be hard to resist adding a couple hairdryers pushing 10psi

Hardware is nowhere near stock, although it will use mostly factory-type sensors.  Injectors are FiTech units that (aside from having Bosch style connectors) should be pretty transparent.

alfadriver said:

frenchyd said:

In reply to Curtis :

This may be a stupid question but why couldn't you grab a flex fuel ECM from a junkyard car and use that switching sensors to be compatible ?  

Why in the world would you buy it used when you can get them brand new???

Or better yet, set your system to not even need one.

Factory ECMs have a massive amount of flexibility.  No aftermarket has that covered.

For fuel flow calcs figure 1.5x (50% more) for E85. If you can max 55's on the motor, go to 80s.

Paul_VR6 said:

For fuel flow calcs figure 1.5x (50% more) for E85. If you can max 55's on the motor, go to 80s.

I think 80s might be overkill in a flex situation when it's on gas.  Might be hard to control them at low loads?

No need to get another ECU. All of the truck ECUs are equipped to read a flex fuel sensor. The tricky part is getting the right tune into it that has the ability to read a flex fuel sensor. It is a software issue. Not a hardware issue. 

All of our LS cars use a flex fuel sensor. It's great. Fill it with whatever blend comes out of the pump and go. There are tables in the ECU that will add timing and fuel and handle the rest for you.

If you want I can send you the HPtuners tune off of my Studebaker back when I had an LS and flex fuel sensor working. Then you can copy all of your tables onto my tune and flash it to your ECU. 

You might be confused because in HPtuners there us an option to turn Flex fuel on. That does not do anything if the tune is not right. You have to have the right tune or it won't work. Wish it was more simple, but it is not.

In reply to TheV8Kid :

You can help Curtis out here- on your stock LS tunes, check the flex fuel tables and see what is in them.  If all of the spark tables are identical, then it's not calibrated for both.  If they are, the odds are good that the base calibration just has flex fuel turned on or off.  I was just messing with a car that was supposed to be flex fuel in it, and put E85 in, turned the feature on, and it worked.

Calibrators are a lazy bunch- they won't clear out the tables even if a feature isn't used.  Makes keeping track of stuff super easy.

Curtis- you may just want to keep the whole thing as is.

Curtis said:

Paul_VR6 said:

For fuel flow calcs figure 1.5x (50% more) for E85. If you can max 55's on the motor, go to 80s.

I think 80s might be overkill in a flex situation when it's on gas.  Might be hard to control them at low loads?

80s aren't bad, 120lb/hr and up is tough. 

alfadriver said:

frenchyd said:

In reply to Curtis :

This may be a stupid question but why couldn't you grab a flex fuel ECM from a junkyard car and use that switching sensors to be compatible ?  

Why in the world would you buy it used when you can get them brand new???

Or better yet, set your system to not even need one.

I said it might be a stupid question. But with regard junkyard you need to understand my cheap nature. Since the engine is used and presumably the car is too, buying new seems like an extravagance to my cheap nature. 
On the other hand if I'm a hopeless old foogy and new is $38 while a used one is $15, sure go ahead and splurge.   

frenchyd said:

alfadriver said:

frenchyd said:

In reply to Curtis :

This may be a stupid question but why couldn't you grab a flex fuel ECM from a junkyard car and use that switching sensors to be compatible ?  

Why in the world would you buy it used when you can get them brand new???

Or better yet, set your system to not even need one.

I said it might be a stupid question. But with regard junkyard you need to understand my cheap nature. Since the engine is used and presumably the car is too, buying new seems like an extravagance to my cheap nature. 
On the other hand if I'm a hopeless old foogy and new is $38 while a used one is $15, sure go ahead and splurge.   

Oh... in that case, not a stupid question.  Last I checked a new ECM from GM was in the neighborhood of $550 wholesale, $750 retail.  

TheV8Kid said:

No need to get another ECU. All of the truck ECUs are equipped to read a flex fuel sensor. The tricky part is getting the right tune into it that has the ability to read a flex fuel sensor. It is a software issue. Not a hardware issue. 

All of our LS cars use a flex fuel sensor. It's great. Fill it with whatever blend comes out of the pump and go. There are tables in the ECU that will add timing and fuel and handle the rest for you.

All of them?  Even if it was pre-flex-fuel?  As I recall (have to check the vin again... it's been a while since I bought it) this was a pretty early LQ9.

And I will need a different ECM, only for the IAC driver that I'm lacking, but it's good to know that flex fuel is built in.  Very curious about your tune.  You can send it to me, but at this point I haven't gone down the rabbit hole of EFI tuning.  I haven't even found the rabbit or the hole.  My idea of building an EFI engine is to do the hardware: injector impedance, flow, pressure, fuel line sizing, cam selection, blah blah... then give it all to a dyno-tuner-geek-computer-rainman and guide him through some of what I want.

I'm a theater tech director, so as a metaphor.... I build the physical set so that actors can perform their art.  I work with lighting designers, sound designers, and set painters, so that I can say "in this scene, I want [insert character] to look sullen and guilty, so make the lights look like that."  It is someone else's job to know what colors will portray that, program three universes of DMX-512, decode the protocol of light fixtures from 7 different manufacturers and 4 different decades.  It is the painter's job to provide paint colors and translucency to complement it, and a sound engineer to bandpass their microphone to convey an emotion.  I engineer the physical stuff... the computer geeky stuff is somewhat foreign to me. But dagnabbit, I wanna learn.

I'm very interested in hearing more.  I'm totally old-school and this is my first EFI build.  Ever.  Other than rebuilding a 350 TPI to stock specs for someone.  My idea of tuning a fuel curve is drilling and tapping for an adjustable primary step-up in the air horn of a Qjet.  Not kidding.  The last ignition curve I tuned was spot-welding the advance plate in an HEI to limit mechanical advance.

Let's talk.

alfadriver said:

In reply to TheV8Kid :

Curtis- you may just want to keep the whole thing as is.

Well, if activating flex fuel is as easy as a mouse click and a sensor on the fuel rail, why would I?  Or am I missing something?

In reply to Curtis :

Yep. Any p01 (red/blue connector) or p59 (green/blue connector) can run flex fuel. The only exception there is 98 Camaro, and 97 Corvette. 

The tune I have is for a P01 (red/blue) ECU. 

And it is as simple as a sensor and a tune. That was the one things I didn't like about the C5 Corvette project that the magazine is doing right now. They are running a $1000 system to add flex fuel when all the need is flex fuel sensor ($50) and the right tune. The stock ECU can do everything they want. HPtuners is one of their sponsors too..  but who am I. It's not my car.