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I saw the previous issues on this topic and believe I followed the advice properly, however I cannot get the vehicles to accept IE's biodiesel. I can insert it into the gas station, and fill gas cans, but starting the transfer does nothing. I also cannot use a gas can that contains IE's biofuel. It says it contains 100mb and will not allow me to use it or place it back into the station.

I have configured car-server.toml with:
[machines.gas_station]
#Range: 1 ~ 32767
transfer_rate = 5
#If it starts with '#' it is a tag
valid_fuels = ["#car:gas_station", "#forge:biodiesel"]

and config/car/fuel.toml with:
["car:bio_diesel"]
efficiency = 100
["immersiveengineering:biodiesel"]
efficiency = 100

I have also tried setting fuel.toml to the forge tag:
["car:bio_diesel"]
efficiency = 100
["#forge:biodiesel"]
efficiency = 100

You need to make sure you don't have any other fuel in the car.
When you initially spawn a car it has generic fuel. But after you fueled it once with a specific fuel, you need to completely empty the cars fuel tank in order to fuel it with another fuel.