"Flex Fuel" sensor support
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Author:  ToxicGumbo [ Mon Jun 03, 2019 10:58 pm ]
Post subject:  "Flex Fuel" sensor support

Out here in Kansas, we have lots of corn for cars and wheat for beer. Not much else.

So I hit Fred up about E85 and thought I'd start looking into ideal hardware for sensing fuel composition.

The gold standard of flex fuel sensors used by GM, Haltech, and commonly in the aftermarket scene is Continental's 13577394. The unit has two 3/8” metal fuel fittings, is rated for 400LPH, and has four mounting holes, something missing in most other brands. You can easily pair these up with Doorman 800-085 quick-connectors, fuel hose, and a GM pigtail (OUT, Signal GND, +12V).


There are claims from DIYers regarding a high failure rate of this sensor, but even more so with respect to Continental's earlier models. From what I've read, it looks more like user confusion over proper voltage levels, grounding, and...I'm speculating here based on Amazon's product listing...the use of Chinese counterfeits. I have not seen any evidence with production vehicles to support the sensors simply being crap. With that in mind, here's a list of production vehicles one can pull a sensor from in a car yard, though the sensor itself runs below $100USD.

Installation is pretty straight forward: Fuel regulator -> Flex sensor -> return line to fuel tank.

Author:  ToxicGumbo [ Tue Jun 04, 2019 4:04 pm ]
Post subject:  Re: "Flex Fuel" sensor support

Correction to the above: 3 mounting holes.

Information on these popular sensors is fairly scattered across other EFI project websites, so I wrote Continental and requested white papers on the family line.

Having said that, has the most information I've seen online and all in one place. I'm quite sure everyone else is pulling technical specs from them.

At a glance:

There are three commonly used sensors:
  • Compact: 13577429
  • With mounting holes and short fuel fittings: 13577379
  • With mounting holes and long fuel fittings: 13577394

The compact unit operates from -40C to +150C, the other two only up to +125C.

VCC: 9-18V
Accuracy: +-5% on ethanol
Connector: Delphi GT-150 (using a knock-off female connector requires minor surgery of the sensor)

Part numbers and any other caveats are in the Miata Turbo link above.

Author:  Fred [ Tue Jun 04, 2019 9:07 pm ]
Post subject:  Re: "Flex Fuel" sensor support

Jeff, any chance of a a quick series of the other options, a pic, and the "why not" for each? You have me curious now. :-) Nicely written post!

EDIT: I will read the link unless it's purely about these ones, in which case my question still stands.

Author:  ToxicGumbo [ Wed Jun 05, 2019 4:13 pm ]
Post subject:  Re: "Flex Fuel" sensor support

The MT site solely targets the 3 Continental sensors I referenced above. In the absence of official docs from Continental, that's the most information I can find anywhere.

One important detail I missed in my earlier post: The output signal frequency range is 50-150Hz, with a higher frequency range representing contamination, 0-5V.

These Summit Racing photos show the three models:

13577429 ~$50USD

13577379 ~$80USD

13577394 ~$75USD

These are all intended to be identical in operational specs, though the first one, 13577429, has the higher operating temp max I mentioned earlier, but is the one model without bolt-based mounting options.

The shorter posts on those first two have been very difficult for people to work with, particularly in the second, 13577379, where everything gets crammed together. This has especially been a problem when aftermarket fittings don't fit quite right and leak. Due to this, I'm partial to the third model, 13577394, since it has both reasonable mounting and clearance.

Here are a few randomly ripped photos of the sensors with misc arrangements:

Imagel Image

Image Image

Image Image

Since I can't find these anywhere else and haven't yet heard back from Continental, here are some direct links to a few photos posted in the MT thread:



Image Image

Author:  ToxicGumbo [ Wed Jun 05, 2019 8:51 pm ]
Post subject:  Re: "Flex Fuel" sensor support

Most commercial and non-commercial EFI solutions/projects I’ve looked at appear to gravitate to this sensor family, quite a few of the former simply rebranding it with their company logo and upselling it.

Pretty much anything other than the genuine Continental units (found most easily and affordably under the “AC Delco” branding) appear to be older, counterfeit, part of a conversion kit, or substantially over $100USD without any immediately discernible technical benefit.

I haven’t delved into what Ford, VW, and the Asian companies are using, but will attempt to provide that answer in this thread.

This one also looks promising:

Author:  ToxicGumbo [ Wed Jun 12, 2019 5:42 pm ]
Post subject:  Re: "Flex Fuel" sensor support

The only other production vehicle sensors I could locate were these two for Ford/Mercury/Mazda and GM vehicles, which appear to ultimately be from the same source. That is, the earlier versions were by Siemens, which sold off its automotive parts division to Continental around the same time this design was popular.

You can see that the mounting and some of the shell has changed somewhat between variants, but it's unclear about the sensor or operation. You can still buy the units from Ford Parts or GM/AC Delco.

Ford (Siemens) F6DF-9C044-AA F6DZ-9C044-AA YL5A-9C044-AA
YL5A-9C044-BA YL5H-9C044-B2A YL5Z 9C044-BA
: ~$200-600 USD
Image Image

GM (Continental or rebranded as AC Delco) 12570260: ~$300-500 USD

Author:  Nige [ Sun Apr 05, 2020 10:16 am ]
Post subject:  Re: "Flex Fuel" sensor support

It seems that many years ago (pre-2010) I used a GM one judging by the fittings, and made an ethanol tester for Toyota Race Series.
Appears like they're all the same setup, linear 50Hz=0% to 150Hz=100%, and the pulse width is fuel temp. We split the signal into 2 inputs of a Motec ADL2 dash and had one measure frequency, and the other measure the pulse width. We then had a custom display made and mount the whole thing in a shoebox sized box to look all professional, with Speedflow fittings on the outside to connect to.

We had one "incorrect" reading, which turned out to be old fuel that had absorbed water. I can't remember which way that pushes the signal but it was noticeably off.

/necro :D

Author:  Fred [ Thu Apr 09, 2020 11:32 am ]
Post subject:  Re: "Flex Fuel" sensor support

Thanks for the story! Necro welcome around here where almost every thread is years old :-D

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