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Best location for flex fuel sensor

Ethanol & Flex Fuel Tuning

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Discussion and questions related to the course Ethanol & Flex Fuel Tuning

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Hi I was wondering the best location to mount a flex fuel sensor. I originally had mine mount on a pressure line just after the fuel rail but have been told it should be on the return after the pressure regulator. I had no room in my engine bay for this. So I mounted the sensor in the boot beside my swirl pot and was going to put it on the return line there. But have been told again it needs to be just before the fuel rail .

Can you advise ?

Irrespective of where you put it, there is going to be a slight delay one way or the other between what's in the fuel rail/injectors and what the sensor is reading. Probably the best thing is to have it as close as possible to the rail to minimise that.

I always put it in the least intrusive, least flow restricting area, so usually in a return line by the tank. I don't really use fuel temp in any active correction maps usually and if your ethanol content is changing on the fly often enough to cause you issues I think you've got bigger fish to fry.

all that said, I'm sure there are different rules one should follow for a returnless port or DI system.

Ok thanks for the replies .

Would mounting the flex fuel sensor between my inline fuel pump and fuel rail be any good ? It would be mounted in the rear of the car soo a little bit of length of fuel line till it gets to the fuel rail would this have a big effect on tuning? . I have taken the flex fuel course from HPA.

The only issue I have is my loom is already made to have the sensor in the boot thinking it was going to be on the return line. But now taken the course it seems it should be better on the feed line . It's not a huge horse power car. Round 500 Bhp


David's correct, I was overthinking it.

There may be a momentary conflict in fuel and mapping, but it would be when the pump would first be activated, when ignition first turned on, and the original fuel would be flushed almost immediately, to be replaced with the new blend. Might be a little reluctant to start, if that, but when fuel and map match up it should all be fine.

Does engine vibration adversely effect the FF Sensor’s operation? I was going to mount mine on a bracket under the intake manifold, on the -6 return line, before the Pressure Regulator…the Haltech sensor appears to be a -6 so no added restriction to the system, it’s close to the rail so read time delay should be minimal, but the vibration is an unknown for me.


~Rich Laws

Akron, OH — USA

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