Ethanol / Flex Fuel Sensor
 

Hey Guys,

Hope all is well.

I finally sorted out my start up issues last month and got the car running well.

Once I added ethanol and raised the boost we had issues with the fuel pressure dropping and realized the additional fuel pumps weren't activating, we sorted that problem out easy.

Took the car out for a test run on ethanol and it went into limp mode again, fuel pressure is okay but the ethanol sensor isn't reading the ethanol content correctly under load forcing the car into limp mode.

My Flex sensor is currently on the OEM return line after the FPR. Do you guys think that the flow on the return is too high for the ethanol sensor to read correctly? As I don't face this problem on the pump gas running the same boost (1.7 Bar).

1- Has anyone faced this issue before?

2- Is the solution to split the return line into 2, and have one line going into the sensor and the other directly back to the tank (Picture below). My concern is if the current return flow is low then how does splitting the return solve the issue?

3- Should I move the sensor to the feed line? Split it into 2 and feed one through the sensor? But wouldn't that restrict flow?

Any help or ideas would be appreciated!

From what I have been told by a few tuners in regards to the placement of the sensor needs to be as close to the rail as possible. On my Syvecs setup on the 996TT and my brothers ProEFI 112 on his 997TT the sensors are literally within a few inches of the Fuel Pressure Regulator on the return side.

I originally had my Syvecs plumbed in the middle of the car on the return line, but it was providing incorrect Ethanol Content because it was so far down the line. That's when my tuner had me move it right to the return on the regulator so it was providing the best readings of E% so the Syvecs flex fuel blending could work correctly.

the picture you posted is how i have it setup on my car in the return and it works fine. you definitely do not want to put it in the feed line.

Have you checked to make sure the FPR is not faulty?

Thank you guys for the input.

Is it too much pressure or too low pressure on the return line that's causing the sensor not to read correctly?

Prodigy, if it is too low pressure, then wouldn't the bypass not solve the problem as the fuel flow is too low for a reading? And do you have the flex fuel sensor on the FPR side (right) or the feed side (left)?

I'm just so bummed that I need to drop the engine again to do this, I have at least dropped the engine 5 times since my engine was done lol.

So I just want to make sure of the right solution before going at it.

Thanks again

No I haven't checked the FPR specifically. But the car is fine on pump gas at the same boost level, I don't think it could be the FPR? Fuel pressure is fine and isn't dropping, its just the ethanol content reading cuts and causing the car into limp mode.

All be it a different platform, but I run my sensor in the return line post FPR on my Supra without any content reading issues. Even at idle I can see the changes while filling the tank if the car is running.

I think you would have to be running your fuel system on the ragged edge for there not to flow in the return line. but theoretically that is possible. also there are multiple flex fuel sensors available now. the reason why I made a bypass for mine was because it wasn't keeping up with the return after pressure has gone up and then let off boost. what regulator are you using by the way?

Thanks for the input, my flex fuel sensor is working correctly and I too can see the ethanol content changing when filling pump gas with ignition on. Also the car runs fine on ethanol at WG pressure (0.8 Bar) so it only happens under higher boost and load.

Thank you for the input, the sensor is wired correctly and I am getting the readings, its just under heavy load the ethanol content reading drops, causing the car into limp mode.

Hey Prodigy,

My Fuel system uses:

1- 2 stock pumps and I have 2 additional Pierburg pumps that activate by boost the first one activates at 1 Bar and 2nd at 1.4 Bar.
2- Stock fuel rails
3- Stock 3.8 Bar FPR
4- Asnu 1500cc Injectors

I have attached a picture of the log my tuner sent me, if I understood correctly from this picture is that my ethanol content drops forcing car into limp mode, and then my fuel pressure drops as additional fuel pumps are shut off due to no acceleration/boost.

Picture Keys:
1st Green line = Fuel Pressure
2nd Green Line = Ethanol Content
Blue Line = RPM
Pink = Map

Note: This run started on 2nd gear, and car went into limp after the shift to 3rd

how much power is your car making that you are trying to use 4 fuel pumps and a stock FPR??


few things I see is that FP is not rising 1 to 1 and then in 3rd gear when it cuts boost the fuel pressure actually spikes even higher, that's because the regulator cant bypass all the fuel from all your pumps.


I would revisit the return side of your fuel system. either get new rails, or modify stock rails ( 2x driver side rails ), don't use stock regulator and get a nice Weldon one.

What FPR are you using?

he posted that its stock

Sorry about that, OP I would look into adding a Weldon FPR as those have one of the largest orifices out of most FPR on the market today.