Discussion and questions related to the course EFI Wiring Fundamentals
I'm trying to connect a variable resistance type fuel level sensor to an AEM Infinity ECU on our 2014 Camaro Z28 Race car. Do I need a pull-up resistor to change the signal from resistance to voltage? What is the placement of the restore if needed. What is the best way to construct the custom table for the input values if necessary.
Unfortunately I'm not familiar with the AEM software, but yes, you'll need to add a pull up resistor. If there is an option to enable one in the software, this will be best, but you can absolutely add one externally.
For the value resistor to either choose in software or add externally, you'll need to measure the resistance values of your fuel level sender when it is reading a full tank and an empty tank. If you can get those and post them up here we can select a resistor value and create a calibration curve. Selecting the resistor value can sometimes be a little involved, as if the fuel level sender has relatively low resistance values, we need to take the overall current flow (and thus power dissipation) into account. Because its pretty late model, it most likely wont have been driving a gauge directly, so this likely wont be a concern. I tend to choose a pull-up resistor about half of the maximum resistance the level sender has, which gives a voltage range of around 0-3.3V...
Cool piece of gear, but you would need to be able to configure the AEM to read the CAN data, and I think its CAN profiles are pretty locked down, plus you'd also most likely still need to add an external pull-up resistor to get the Analogue to CAN interface reading the variable resistance signal of the gauge sender
Thanks Zac. That's a big help and I'll get the resistance values in the next couple of days. I come from an industrial instrumentation and control back ground so the principals are the some for pressure, flow, level, temperature, digital, pulse, etc... I'm just learning how things are done in the auto and motorcycle racing worlds but it has been fun so far. Can't wait for the advanced course!
Bastard forum lost my long reply when submitted...
You will also need heavy filtering to slow down the effect of fuel sloshing around. The AEM may have some user configurable input filters so that is something to confirm.
Most fuel level sensors are very low resistance so the pull up will be a bit of a compromise between good range and loading up the 5V reg too much. Below is a pic from our forum of a drawing I done for another user. This will probably work for you if your sensor resistance is less than about 200ohms. To give it a quick explanation, the 100ohm resistor is the pull-up. The 18Kohm resistor an 1000uF cap is what you call an "RC Filter", this particular combination of values will filter the input over a time period of about 1minute.
Sorry about the multiple posts. this forum didnt like a symbol I had in the text and kept deleting my post.
Thanks Adam. I was wondering how to dampen the signal as we're running the stock fuel tank in the 2014 Z28 for a road racing application. I'm still trying to find information regarding the purpose of the car's primary and secondary fuel level sensors.
Some vehicles used a separate sender for the low fuel warning - whilst I would have expected that to work of the regular fuel level sender and be triggered by the ECU in a modern vehicle, could that be it?
Thanks for the reply. It's possible the secondary could be used for that. I'll post if I find a definite answer.
If the tank is an odd shape, to fit over the driveshaft tunnel or similar, sometimes there will be two fuel level senders, one for either side of the tank, and the ECU / dash reads both so it can know how much fuel there is left overall.
So, if that is the case how would I use the two signals to provide a real tank level with an aftermarket AEM ECU?
You could still add the same RC filter to this.