DIY Flex Fuel Kit - How to Save Big (and Buy Individual Pieces)

[Somac]

Let me preface this whole thing with this:

If you are not willing to do custom work yourself and don't want to mess with anything or piecing together parts, just buy the Flex Fuel Kit from Cryotune. It will all go together without guessing and without anything on your end other than just installing the parts.

 

For everyone else, read ahead.

 

Cobb finally released support for flex fuel tuning for Legacy GTs, Outback XTs, and Forester XTs. This means their AccessPorts will now allow you to do all kinds of cooler stuff, even beyond just Flex Fuel. Dave @ Cryotune made a couple great posts detailing all the things the new software is capable of as well as the details of the flex fuel operation.

 

https://legacygt.com/forums/showthread.php/cobb-flex-fuel-and-you-why-and-much-276632.html?t=276632

 

https://legacygt.com/forums/showthread.php/cobb-custom-features-and-you-even-without-flexfuel-enabled-276622.html?t=276622

 

With the release of flex fuel support, Cobb is obviously first to the market with their flex fuel hardware, too. This means they get their first-to-the-market price premium, especially when the LGT kit is already $200 more than the other platforms.

However, these kits have been around for a while for other platforms, so there's a lot of knowledge readily available on how to avoid paying the Cobb premium.

 

Much of this information is going to come from SurfGuruJeff's NASIOC thread that covered this topic when flex fuel support was released for WRXs and STIs a couple years back.

 

https://forums.nasioc.com/forums/showthread.php?t=2810122

 

Keep in mind, all of this assumes you're going to be using a Cobb AccessPort, so you're still using their product and their software regardless, but the hardware is mostly generic that doesn't need to be so expensive. Everybody's gotta make a buck somewhere in the process. Open source guys can still use all of this hardware, but if you're open source, you probably haven't been waiting for Cobb to finally release software support for flex fuel.

 

Let's talk about the pieces of the whole kit. Here's a link to the actual full kit from Cobb:

 

https://www.cobbtuning.com/products/flex-fuel/subaru-flex-fuel-package-3-pin-lgt-obxt-2005-2009

 

The pieces are:

 

1) The ethanol sensor

2) The flex fuel module

3) The fuel lines

4) The fuel pressure regulator

5) Pressure sender for fuel pressure

6) Pressure sender quick disconnect line adapter

7) Harness for pressure sender

 

I talked to someone at Cobb today. He gave me these prices for individual parts of the kit:

 

1) Flex Fuel Sensor: $100.00

1.5) Flex Fuel Bracket,OBXT 05-09: $25.00

2) Subaru Flex Fuel Module: $375.00

 

 

7) Subaru Custom Finished Harness , 3 Pin Over mold Connector With Cobb Logo - $95.00

 

You'll notice there are several items missing off that list, and that's because we really don't need the rest since they're all generic. Since my car has AN fuel lines with an adjustable FPR already, I requested pricing for the kit with no FPR, no lines, and no fuel pressure sensor.

 

So, let's start with looking at what we can replace, what it's a good idea to get from Cobb, and what's actually necessary from Cobb:

 

1) Flex fuel sensor - this is just a generic GM ethanol content analyzer that every flex fuel kit in the world uses. They're cheap, they're reliable, they're ready available, and most importantly, they're cheap. They can be found for $50-70 anywhere. I believe even a GM dealer will charge around $65 for an OEM replacement.

 

ACDelco Flex Fuel Sensor - $56

 

1.5) Flex Fuel Bracket - DIY. Just some 14-or-so gauge steel with a couple small bends, some cuts, and some holes. It's up to you whether it's worth it to save $25. You can probably buy a sheet of this at your local hardware store then paint it yourself.

 

2) The flex fuel module - this is actually basically a converter to take the 50Hz-150Hz signal from the ethanol sensor and translate it into a 0V-5V signal the ECU and the AccessPort can understand. These usually plug into the rear O2 sensor for power, the ECA for its signal, then feed information into the TGV connector so the ECU can actually receive the signal. This is a specialized piece, but there is someone out there making these - Flexconverter.com's BlueFlex kit.

 

Blueflex Flex Fuel Module - $180

 

According to a user on NASIOC (emphasis mine),

 

arguably the simplest solution is to buy the universal blueflex unit here and just wire in a tgv connector and 12v power. i believe this was sold previously and now the creator has pulled the 08+ compatible version from the market due to a agreement with cobb.

 

Now, you can DIY this part, too, as the people have done in the NASIOC thread. However, when it comes to this, there is a lot of fine adjustment they had to do and a lot of finagling that sometimes we'd like to just work and pay a little more for it.

 

3) The fuel lines - These are again just generic fuel lines with some quick disconnect connectors on them. These will be worthless to you if you switched to AN fuel lines in the engine bay. If you didn't, then you can make these yourself with some Dorman quick disconnect fittings from an auto parts store.

 

3.5) AN fittings - Cobb sells quick disconnect to AN fitting adapter on their site for $45/pair. These look like they're just regular Russel fittings with a 100% markup.

 

Push-on style for $7.65/each

 

Thread-on style (same style as what's in the Cobb kit) for $10.69/each

 

4) The fuel pressure regulator - If you've already got an aftermarket adjustable FPR, this is worthless you. To Cobb, it's worth $200 and why our kits are $200 more expensive than everyone else's.

 

If you've still got stock fuel lines, now is the time to do the STI FPR conversion, as written by our very own awesome covertrussian in his DIY guide here:

 

https://legacygt.com/forums/showthread.php/install-04-07-sti-fuel-pressure-regulator-fpr-and-use-263825.html

 

5) Fuel pressure sender - This is just a regular Autometer pressure sender that can be had for ~$100. Autometer 4590-0023-12.

 

https://www.amazon.com/Auto-Meter-2246-Pressure-Sender/dp/B000CIH39Q

 

6) Fuel pressure sender quick disconnect adapter - Again, if you've got aftermarket lines, this is worthless to you. Cobb sells this part individually at a cost of $45.

 

If you've got stock lines, this looks like the same thing as the Glowshift fuel pressure sender adapter that Glowshift makes, but in 5/16" variety rather than 3/8".

 

https://www.amazon.com/GlowShift-Quick-Connect-Pressure-Adapter-Mustang/dp/B0792DXKJX

 

7) Harness for pressure sender - This is just a regular harness to go from the Autometer sender to the car. Cobb sells this part individually for $95. A replacement harness can be purchased from Autometer for $24, then you can add your own plug.

 

That's the basic rundown of all of these parts. Some work will be needed on your part to make the harnesses, make the parts work with your fuel lines, figure out where to install them, etc. But all of this should work exactly the same as Cobb's kit. It even gives you the choice of where you want the readings to go, whether it be the TGVs or rear O2, depending on what you have deleted.

 

Now, as far as what you should and shouldn't get, it will all come down to opinion and the level of work you're willing to put in.

 

Source it yourself:

Ethanol sensor

Fuel pressure sender

AN adapter fittings

 

Up to you:

Flex fuel module

Pressure sender harness

Ethanol sensor bracket

Fuel lines

 

Get from Cobb:

Pressure sender adapter

 

The sensor is obviously just a generic one with a Cobb label. The pressure sender they didn't even bother putting a Cobb label on - it's an Autometer sender plain as day. The AN adapter fittings for the guys that did an AN conversion are just generic stuff, too.

 

The module is where you get the biggest savings, but also may have the biggest margin of error - it seems to require adjustment and playing with the offsets/scaling; I lean more towards buying this from Cobb for a trouble-free experience. The pressure sender harness is a super simple harness, but for a little under $100, it's often not worth it to source the connectors yourself, measuring out the whole harness, and making it work; it's up to you to decide if you want to save here. The bracket is obviously just dependent on if you want to take the time to make a bracket and save $25; not everyone has the metal or the tools and the Cobb will have the cleanest install. The fuel lines, bringing up the AN for the last time, are worthless if you have the AN conversion; if you don't have AN lines, you can still DIY this, but it's usually worth it to just buy from them and not mess with it.

 

Buy the pressure sender adapter from Cobb because I can't find a direct match for Cobb's unit. I am not sure if the sizes are listed incorrectly and it is indeed just the Glowshift unit that they supply or if Cobb had their own made (I can almost guarantee they didn't make them in-house), but until then, this will be a "Buy from Cobb" item.

 

If anything here is wrong, feel free to correct me. I'll try to keep this upost updated as information is corrected. I'm no guru or master, just trying to save some money.

 

Updated 11/25/2018 - Cleaned up formatting + disclaimer

Updated 11/27/2018 - Source Recommendations

[LeGiT_Flat4]

Thanks for posting all this info Somac. Well done.

 

I'm currently running the BlueFlex ECA with a generic flex fuel sensor so theoretically I'm well on my way. At the moment I'm just using it to monitor ethanol content with their app but I had assumed that if Cobb ever released flex fuel I would be able to leverage my hardware in conjunction with their software and an AP. I should be able to feed the signal to the ECU without much additional effort. Presumably I can use the rear o2 sensor input for that but I also have tgv deletes that I plan to install so I could go that route. I'm scratching my head a bit with Cobb's decision to delete the factory fpr assembly and then charge an extra $200 for a new fpr. I'm still researching their design but I installed my ff sensor on the fuel feed line after the fpr assembly like the Delicious Tuning kit is designed. Cobb's design appears to put the ff sensor on the return line. Maybe the 5/16" (stock line) to 3/8" (ff sensor) back to 5/16" creates some possible undesirable irregularities not ideal for the feed line. Either way I've got quite a few things to figure out since I plan to also convert to top feed injectors. With all that, I'm still considering just purchasing the Cobb kit to make it that much easier and also give me a little more peace of mind that it would be warrantied and I'd have some support if needed.

[Somac]

Thanks for posting all this info Somac. Well done.

 

I'm currently running the BlueFlex ECA with a generic flex fuel sensor so theoretically I'm well on my way. At the moment I'm just using it to monitor ethanol content with their app but I had assumed that if Cobb ever released flex fuel I would be able to leverage my hardware in conjunction with their software and an AP. I should be able to feed the signal to the ECU without much additional effort. Presumably I can use the rear o2 sensor input for that but I also have tgv deletes that I plan to install so I could go that route. I'm scratching my head a bit with Cobb's decision to delete the factory fpr assembly and then charge an extra $200 for a new fpr. I'm still researching their design but I installed my ff sensor on the fuel feed line after the fpr assembly like the Delicious Tuning kit is designed. Cobb's design appears to put the ff sensor on the return line. Maybe the 5/16" (stock line) to 3/8" (ff sensor) back to 5/16" creates some possible undesirable irregularities not ideal for the feed line. Either way I've got quite a few things to figure out since I plan to also convert to top feed injectors. With all that, I'm still considering just purchasing the Cobb kit to make it that much easier and also give me a little more peace of mind that it would be warrantied and I'd have some support if needed.

 

There's nothing wrong with buying the Cobb kit! It's there exactly for people that want a trouble-free, no-hassle purchase and install. Everything is all in one kit with clear instructions and it's a straightforward process. That's essentially what you're paying for.

 

For other people that are willing to do some more work in exchange for saving a bit of money, that's what this is for.

[cpx4656]

Okay so the 2005 FXT kit comes with no fuel presure regularlator and looks very similar to the LGT one. It also comes with the 3 pin harness. So that kit could definitely be adapated using parts listed in this thread.

[LeGiT_Flat4]

Seems like it would work but the FXT kit appears to have a different bracket so you may have to come up with your own mounting solution and it may also require additional/different fuel lines so installation probably wouldn't be quite as simple. But if you're already running aftermarket lines and FPR, then I can see going that route for sure since who wants to pay a bunch extra for an fpr you wouldn't be using.

 

The other consideration is the same as mentioned above with a full DIY solution-- Cobb may not be interested in supporting any problems you might have since even though you would be using their product, you wouldn't be using the setup they intended for your particular application. YMMV.

[Winrahr]

Cobb was able to let me order just the sensor and the module, which is the same price as Somac stated above at $100 and $375. Quite a bit more expensive than the DIY route but it's worth it for me to retain support from Cobb.