Flex Fuel Sensor Problems

[neongreen]

I installed a Ford Flex fuel sensor recently (as shown below) and so far as I can tell, it outputs a frequency signal (as it should).



However, while taking a drive to let VE Analyze Live do it's thing, it would suddenly get horribly lean and misfire. Looking at the logs, it seems the E85 fuel correction value was doing funky things, and destroying my tune. The e85 fuel correction value would jump between 100-103 and the fallback value of 163.



Does anyone here have experience with this sensor? Is this the sign of a dying sensor, or is there something else I should look at?

[jsmcortina]

[neongreen]

Is there a way to cut logs into smaller pieces? I tried to upload, but the file size was 9 megs, which apparently is too big.

[hybrid]

You should be able to do it in excel, but megalogviewer can do it too. You might need the paid version to do it though.

[neongreen]

I think I've got it figured out.

2017-02-04_12.50.10_trim.csv

[neongreen]

2017-02-03_19.45.05.msq

[jsmcortina]

In the datalog your "Ethanol Percentage" is almost always at 1% which indicates an error condition.

Does your multimeter have a frequency setting? It would be worth measuring the output from the sensor to see what frequency you are seeing. Something is clearly wrong with the flex measurement.

James

[neongreen]

Unfortunately my multimeter doesn't read frequency.

I bought another old ford flex fuel sensor, installed it - same result, fuel composition reads 1% and defaults to full ethanol correction. I know that I'm getting 12v to the sensor, and ground is fine. The signal wire has continuity all the way back to the ECU.

Now I'm wondering about the flex fuel circuit and if something needs to change there.



The current MS2 Extra manual shows 2 resistors, a pull up (seen on the right here) and another one in line with the JS7 pad (seen at the top of the pic). Previous manuals show only the pull up resistor. Is it possible that this is causing problems?

[neongreen]

Built a sound card oscilloscope, which is actually very cool and cost about 50 cents to build.

The sensor appears to be putting out a 40hz signal. Does anyone know what this means?

[slow_hemi6]

Sensor range is 50hz to 150hz representing 0% ethanol to 100% ethanol.
Ethanol% = [frequency(Hz) - 50]
1mS pulsewidth = -40 degrees and 5mS pulsewidth = 125degrees for the temperature range.
degC = [ 41.25 * Pulsewidth (ms) ] - 81.25

40hz is going to be seen as an error.

[neongreen]

That's correct. The ECU uses the fallback multiplier when I enable flex fuel input.

The real question is this: is the sensor bad? Do i need to replace it, or is there something else going on?

[neongreen]

As stated above, I have two Ford style Flex Fuel Sensors. One I picked up in a yard, and the other I bought off eBay. Both are dead. I ran some denatured alcohol and gasoline through both tonight, both had the same result on both fuels: 39.9Hz. Time to buy a GM Continental sensor.