Flex Fuel Sensor reading 100%

2006 Corvette, E-Force - 10lbs boost, Heads, CAM, E85 Flex Fuel. I have recently been experiencing an issue with my DSX Flex Fuel Sensor. At start-up the sensor will read Ethanol Fuel % at 80.4 to 81.6%. After several minutes of warm-up (5-10 minutes) the Ethanol Fuel % goes to 100%. After a few hours of non use, at start-up the sensor will again read at the 80 to 81% range. I have been told by an experienced tuner that moisture/condensation can cause this issue. Not sure of how that all works but when it does happen and I'm at the track waiting to go WOT in the quarter mile, its somewhat disconcerting. I'm looking for a work around in the tune when this happens. Currently my Engine>Fuel>Flex Fuel>Sensor Default Percentage is set to 70%. What has to happen in order for this Sensor Default Percentage to replace the sensor reading of 100%? If I unplug the flex fuel sensor, the Ethanol % goes to zero and not 70%. I'm hoping someone has already worked through this issue and I'm not the first to experience this. I have talked with the Tech's at DSX Tuning and they apparently have not had to face this problem. I may just order another GM Flex Fuel sensor but that may not fix the problem. Any idea's?

This is not normal, I would say with almost certainty it's a hardware issue, check your wiring and if that is good replace the sensor. I wouldn't try compensate for a bad sensor in your tune.

Wiring is good and like Big Tuner, I believed from the start that the sensor was going bad. However, DSX was very skeptical of a bad sensor as they could not recall of a sensor problem like mine that was the result of a bad sensor. I have a new sensor on the way and should have it installed by Monday if it arrives as scheduled. I will report back on Tuesday the 23rd if the new sensor fixes the problem. I believe heat may be the issue. When the sensor goes to 100% the oil is at 160 degrees, coolant is at 175 and the sensor also reads 175 degrees when scanned with my infrared heat scanner. Like I stated earlier, at start-up it reads as expected. Only after setting at idle through warm up (5-10 minutes) does the sensor reading go from 81% to 100%. I am still wondering how or when the Flex Fuel Default Percentage is activated in the tune. I set mine at 70% but have no idea if this has any impact on the tune of the motor or not. What would have to take place for this to have any bearing on the tune?

Replaced the DSX Flex Fuel Sensor with no change in the outcome. Right at 7 minutes after initial start, the flex fuel ethanol content goes from 80% to 100% which is an indication of contaminated fuel (moisture in the fuel). I have added Sta-Bil 360 and Heet but neither has had any effect on the sensor readings. I will just have to use up my fuel (E85) and replace with a fresh E85R Fuel. The sensor is doing just what it is supposed to do which is to peg at 100% when encountering contaminated fuel.

This is not normal, I would say with almost certainty it's a hardware issue, check your wiring and if that is good replace the sensor.

The signal from the alcohol sensor is a frequency. 0-150 Hz from memory. Is the wiring for the sensor routed near anything noisy?

Have you tried a different tank of gas?

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Originally Posted by Alvin

The signal from the alcohol sensor is a frequency. 0-150 Hz from memory. Is the wiring for the sensor routed near anything noisy?

Have you tried a different tank of gas?

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Maybe use shielded wire?

The output of the sensor, a single white wire which goes to a pin-out on the E38. The output wire is routed via a heat shield sleave from the sensor to the E38. My next step will be to burn through the fuel I have in the tanks and replace with fresh E85R which I purchase from Bandimere Speedway via 5 gallon jugs. I will insure the jugs are clean and dry when refueling. As mentioned, the output of the sensor is a frequency which I believe ranges from 0 to 190Hz with any output > than 150Hz an indication of fuel contamination (moisture in the fuel). Will report back on the results of fresh fuel in the tanks.

Added Fresh fuel (E85R) after burning down what was in the tanks. Fresh fuel fixed the problem. The flex fuel sensor will peg to 100% when it reads contaminated fuel (fuel contaminated with moisture).

I had a similar issue on a 2010 Camaro SS E38. The flex tune worked perfect for several years. I added a VP Racing E85 additive to the fuel. It immediately showed 100% E on my gauge. After driving a bit I added 5 gallons more of E. The % came back down to ~80%. While driving it would sometime spike back to 100%. So I added more of the VP additive and it went back to 100%. I then changed the sensor out and no longer am running the additive and the sensor is now steady in the low 80's.

If any water gets through the sensor it will read 100