E90 Fuel level sensor, wired to the Infinity setup? | AEM
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Andrew C
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E90 Fuel level sensor, wired to the Infinity setup?

I know this can be done, with a resistor on other ECUs, but, does the Infinity have internal resistors on any of the analog input channels?  Would hate to be redundant on resistance and cause an error on the CD7.

  

AEM_SB
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Joined: 06/07/2014 - 14:29
If you're not already using

If you're not already using the Analog_5_Temp input (pin C2-16 on the Infinity ECU) this gets called 'AirboxTemp' in the Infinity software, and it's broadcast via CAN so the CD7 dash could be configured to use it.  The input has a built-in 2490 ohms resistor, which might work pretty well if the OEM fuel level sensor has an operating range that goes up to 500 or 1000 ohms. If the resistance of the OEM fuel level sensor is much lower than the ECU's built-in resistor, there will be a very small voltage swing from empty to full which means and the measurement won't be very precise. Watch the channel Analog_5 [V], I would want to see at least 1.0V difference between the full and empty measurement.

 

Hope that helps,

SB

 

 

soardrft
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Joined: 04/05/2018 - 20:17
My float type fuel level has

My float type fuel level has the following ohms:
Full - 4ohms +/- 1.0
Empty - 110ohm +/- 7.7

Does the infinity have an input for a resistor that i can switch to log my fuel over CAN?

 

John Randolph

AEM_SB
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soardft, I'm going to assume

soardft, I'm going to assume you have a 30-7109 Infinity ECU installed in an E46 since you replied to this post in the E46-specific section of the forum.

Your resistance values of 4-110 ohms will translate to voltages of about 0.01V - 0.21 V when connected to pin C2-16 of the ECU. The measurement resolution would be much better if you added a pullup resistor in the harness, but it may be acceptable using the default circuitry inside the ECU. You can adjust the values in the AirboxTemp [C] table so that 4 ohms = 100  and 110 ohms = 0.  This channel gets broadcast to the CD7 dash, the default name for it will be 'AmbientAirTemp_raw' when you are using any of the Infinity dash setups. Then you can insert a new 'output channel' in the DashDesign software to rename the channel from AmbientAirTemp_raw to 'Fuel Level' or whatever you want to call it. 

Hope that helps, let us know if anything is unclear.

SB

oldmanlance
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Hi SB.

Hi SB.

While we are on this topic, I measured the ohms of the factory saddle tank sensors.  Would like to know if either of these readings can be used for an idea on fuel level.  I have the Infinity and CD7.

Passenger side:

Full:398,  Half: 250  Empty 70

Drivers side:

Full:315, Half: 200, Empty: 70

Thanks.

AEM_SB
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Those values aren't an ideal

Those values aren't an ideal match for the ECU's pullup resistor, the measured voltage for each sensor will be around 0.7V when full, 0.5V at half full, and 0.1V when empty. That's probably good enough to act as a fuel gauge, although I would want better accuracy if this was an endurance race team trying to predict exactly how much fuel needs to be added before coming in for a pit stop.

 

Adding a 470 or 1000 ohms resistor in parallel will improve the accuracy of the measurement, although the ECU's calculated 'resistance' values won't match reality since you will have changed the total resistance of the pullup circuit.

 

Hope that helps,

SB