Siemens/Continental flex fuel sensor?

[triangles95]

https://www.dragtimes.com/parts/Flex-fu ... 09695.html Do any flex fuel sensor besides the GM one work? I was looking at the Siemens/Continental part# 13577379. I don't see any information out there. Also where does the flex fuel sensor typically go? In the pressurized fuel rail right before the injectors? Low pressure before the fuel pump?

[24c]

I found this description on the net

The flex fuel sensor measures the ethanol-gasoline ratio of the fuel being used in a flexible fuel vehicle. Flexible fuel vehicles can be operated with a blend of ethanol and gasoline, up to 85 percent ethanol. In order to adjust the ignition timing and the fuel quantity to be injected, the engine management system requires information about the percentage of ethanol in the fuel.

The flex fuel sensor uses quick-connect style fuel connections, an incoming fuel connection, and an outgoing fuel connection. All fuel passes through the flex fuel sensor before continuing on to the fuel rail. The flex fuel sensor measures the fuel alcohol content, and sends an electrical signal to the engine control module (ECM) to indicate ethanol percentage.

The flex fuel sensor has a three-wire electrical harness connector. The three wires provide a ground circuit, a power source, and a signal output to the ECM. The power source is battery positive voltage and the ground circuit connects to an engine ground. The signal circuit carries the ethanol percentage via a frequency signal.

Alcohol content information is supplied to the ECM from the fuel composition sensor. The fuel composition sensor has a battery positive circuit, a signal circuit, and a ground circuit. The fuel composition sensor uses a microprocessor inside the sensor to measure the ethanol percentage and changes the output signal accordingly. The signal circuit carries the ethanol percentage via the frequency signal. The ECM provides an internal pull up to 5 V on the signal circuit, and the fuel composition sensor pulls the 5 V to ground in pulses. The normal range of operating frequency is between 50–150 Hz. The microprocessor inside the sensor is capable of a certain amount of self-diagnosis. An output frequency between 180 Hz and 190 Hz indicates that the fuel is contaminated.

I highlighted the bold bit...sort of answers your question. You measure the fuel before it gets delivered, so the MicroSquirt can adjust the ignition & injection. Thanks for the question, I didn't realise these rascals existed...mighty useful if you ask me.

[Bernard Fife]

Triangle95,

Good find on the sensor! That's a great price.

The FF sensors I have seen in OE installations have been in the fuel return line. That's where I would put one. However, since many newer vehicles have PWM control of the fuel pump and no return line, that's not an option, and I suspect before the fuel pump is as good an option as any (the fuel moves pretty quickly through the lines, and the fuel composition changes relatively slowly, so delay isn't really an issue, it's more a matter or keeping the sensor away from heat and alive as long as possibly).

The current code assumes your sensor gives a frequency output that changes with fuel composition (these sensors measure the fuel content by it's changing capacitance, and this is most easily done by seeing how it affects the frequency of an LRC circuit). The current code lets you set up the controller to whatever linear frequency response your sensor gives (see: http://www.megamanual.com/flexfuel.htm and http://www.megamanual.com/mt29.htm#sf ).

If you can't find the response curve, it's easy to generate it on the bench with some gasoline, and then some E85 (or I believe Bruce used 190-proof Everclear!). The fuel doesn't have to be flowing in the sensor, the line just has to be full of the measured fuel (so just a couple short bits of hose, a small funnel, some fuel, and a 5V or 12V supply - you can determine which from the OE vehicle's wiring diagrams).

Lance.

[triangles95]

Thanks for the great info. I"ll do some more digging to see if I can find out how the "cheap" sensor I found works. Sounds likely that I could get it to work.

[GrocMax]

Absolutely no reason the dielectric/temp sensor can't be used on the the return, just make sure its on the bottom of a loop so its always full of liquid. And a fuel temp trim should be based on temp at injectors, which will be more accurate on the rail return, not the inlet.