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Ethanol sensor and fuel pressure sensor issues

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Hi everyone!

This is my first post here so thank you for taking time out of your day to try and help.

I attempted to search this issue but couldn’t seem to find an answer.

issue #1

My ethanol sensor is reading very erratically. I don’t have e85 in the tank yet, however, pump gas here in the states has about 10% ethanol. When the car has the ignition on and the fuel pump is primed, the ethanol gauge shows about 8% ethanol. Once the car is running the gauge is fluctuating between 2%-8% very rapidly. I should not that the sensor is mounted after the fpr.

issue #2

My fuel pressure sensor is reading very low compared to the analog gauge mounted on the fpr. The analog gauge is showing about 44psi with the vacuum line removed, while the sensor (wired into the adaptronic) is reading at about 5psi. The fuel pressure sensor is also mounted after the fpr.

Is this an issue caused by the placement of the sensors? Or something else?

The Fuel Pressure sensor needs to be before the FPR, as close to the injector rail as possible, having it after the FPR means that you are measuring the pressure in the return line to the tank.

#1 I'd suggest starting with a review of all the wiring, there may be a partial break or bad contact that's giving a unstable voltage to the sensor and/or gauge.

#2 addressed.

@blackrex - ok I will try and find a new spot for the sensor

@Gord - it’s pretty simple wiring and all three of the ethanol sensor wires are wired straight into the ecu, I’ve double checked the wiring and it all looks intact. Would the erratic values typically point to a voltage or ground issue, or could maybe aeration in the lines cause it? Its especially confusing because once the ethanol sensor sees fuel that isn’t moving, it reads correctly, however, once the car is on and running, that seems to be when the issue starts.

Are you feeding the sensor with 5V or VBatt?


The sensor is getting 12v from existing pins in the ecu. Not directly from the battery

I've always put my sensor on the fuel return no closer than 12 inches. Only time I've seen erratic ranging of content percentage was with an electrical issue, or a reaallyy suicidal fuel pump.

I should have asked before, but exactly what ethanol percentage sensor are you using - some use a 5V supply, some use a 12V supply? Are all three (?) wired connected to it - ie. is the sensor grounded to it as well?

Here is the unit I make for my customers to install. Continental sensor. Provides content percentage and fuel temp.

Attached Files


its strange that once the fuel pump is off and the fuel is just stagnant in the sensor it reads fine. Only when the car is running is the readings all over the place.

Ya I’m using a continental sensor, the one I’m using is the smaller version tho


im using a continental ethanol sensor, all the wires are going straight to the ecu. It’s pulling 12v from an extra pin on the ecu, 5v pinned to the ecu, and ground from the ecu. It almost seems like the sensor might just be faulty.

I would look at the signals (including power & ground) using an oscilloscope both running and stopped.

Where is your power source from?

I'm using an open ecu power supply, on some cars I'll pull from an open fuse location, as from battery and such the voltage can be very unstable. How did you wire in, crimp or solder? where is your ground and how solid is the contact?


The power and ground is coming from open pins in the ecu. And the signal wire is pinned straight into the ecu aswell. I’m almost certain now that the sensor is just in the wrong place, I’m not sure why. I’ve placed it at the return line after the fpr. I’ve tested a second sensor and still getting the same issue. I may have to plumb into the feed line. I believe my main issue is the sensor isn’t seeing a constant stream of fuel, which is why the readings are so erratic and when the fuel is stagnant in the line, the readings look fine.

The return should be constant and smooth vs the pulsation and turbulence of the feed line. try placing it further away, I go no closer than 18" personally.

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