Flexfuel not updating

[dholloway543]

So ive been driving my flex fuel sensor for about a year now and ive been on e85 for close to 3 months straight now. When I put 91 Oct back in the tank today i noticed that my ethanol percentage was constant at e83. After doing some research it looks as if the sensor was dirty so I did some power pulls and it dropped down to e14 where it should have been. I found on a Honda forum that the flex fuel sensor needs to be plugged somewhere in the fueling loop back ( IE. before the fuel pressure regulator ) in order to prevent something like this.


Does anyone have any ideas on how this can be done or any ideas to help prevent this from happening again?
It seems dangerous to run 91 on an e85 map

[Ashikabi]

Fuel pressure regulator is in the pump hanger so it's not possible to go before it. My FF sensor was between the hardline at the chassis and the fuel rails. To my knowledge this is where all FF kits place the sensor. Might just be bad luck

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[CSG Mike]

It takes a while for fuel to get from the tank to your engine.

You don't want to be doing a pull or loading the engine heavily when you're transitioning from old mix to new mix.

[dholloway543]

Its understandable, I was going on a quarter tank of gas and the flex fuel sensor was still stuck. The only reason why I did it was to see if it made a difference. Maybe i just need to transition fuels more often to keep it from getting dirty. IDK if that would help.

[EndlessAzure]

If you have a flex fuel map, it doesn't matter what your fuel mix is. The sensor will read the fuel mix before it reaches the injector outlet and adjust the map.

The fuel mix doesn't change instantaneously. It needs time to blend in your tank and travel through the lines leading up to the engine bay before it even passes over the sensor or reach the cylinders. That doesn't start until you get a quarter mile or so down the street.

The flex fuel senor shouldn't get "dirty" that easily either because fuel is always flowing over it.

[dholloway543]

I am very aware that it takes time for the ethanol to get to the sensor but I have a gauge that shows my ethanol content as shown in the picture. I burned 1/4 tank of 91 octane and it still showed E83 and i'm curious why or how to prevent it. It used to take a matter of like 5 miles before not >30 miles.

[mrjj]

I see some unexpected behavior from my ethanol sensor as well. I'd like to know if anyone else ever had their sensor "stuck" or reading too high/low?

[Fred E]

If your flex fuel kit is in-line with your port injection line, but your tune favors direct injection during normal driving, it can definitely take a long time for the content to update. In order for the reading for both your gauge and your flex-fuel tune to update, fuel would need to flow through the port injection line, as it does during power pulls.

If this is the case (i.e. FF sensor is in-line with port injection), what is strange to me is how you've only just now observed this, unless you were purposely taking it easy since you've switched to a full tank of 91. If you were on a high E% content, then filled with more E85, you probably wouldn't drive easy immediately since the content wasn't changing much.

Again, if this is case (i.e. sensor is in-line with port injection), one option is to ask your tuner to provide another map that would force the port injection ratio to be higher at all times. You would switch to this map right after filling up, drive for a short while and your readings should quickly update.

Alternatively, you could have your kit's installation modified to move the sensor to be in-line with the direct injection line instead. Moving the sensor would be the highly recommended solution.

Of course, if your sensor is already in-line with the direct injection line, all of my speculation is moot and I have no idea what's wrong.

[dholloway543]

You have indeed found my issue. I believe the port injectors aren't used at all until med to high engine load as to help with low speed pre ignition. Moving the sensor to the direct injectors would blow it up due to pressure so it would need to be moved up the fuel line to before the high pressure fuel pump. Or probably what I'm going to do is just update the tune.

[Ashikabi]

Originally Posted by dholloway543

You have indeed found my issue. I believe the port injectors aren't used at all until med to high engine load as to help with low speed pre ignition. Moving the sensor to the direct injectors would blow it up due to pressure so it would need to be moved up the fuel line to before the high pressure fuel pump. Or probably what I'm going to do is just update the tune.

I'd your sensor is between the hardline on the frame rail and the engine then you don't need to worry about pressure

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