Fuel door release harness

[tmoretta]

"Misnomer"- What I thought was a connection in the right rear corner of my donor WRX to the fuel door is actually the connection to the fuel pump controller. I do know that I do need to include this in my 818 build, but I am confused about the FFR instructions in terms of other fuel tank equipment. The assembly directions only cover the fuel pump and fuel level sensor. According to Subaru wiring schematics, there are three other devices that are not mentioned: The pressure control solenoid valve, the drain valve, and the fuel tank pressure sensor. Now my donor harness includes terminals for these devices, but, is it possible they are not necessary? Also, is it true that I can eliminate the "keyless Entry unit" and all associated wires to source? And, what is the "CRU" unit?

[longislandwrx]

From one of my posts on another build thread regarding the fuel pump controller:


It is a voltage regulator that can drop the appx fuel pump duty cycle from 0%, 33%, 66%, or 100% based on what the ecu is demanding.
If you were to datalog what voltage your pump is seeing you might see it go from 5v-14v's
It will also kill the pump if the engine stalls, something that doesn't happen if you just run the pump off a relay.

Car will run fine if you hard wire the pump, but you'd probably want to tune as you will most likely be running rich. It's there, and already wired and a nice safety feature. I'd use it.


As far as the emissions/evap stuff, The pressure control solenoid valve, the drain valve, and the fuel tank pressure sensor, can all be removed, you'll just need to disable the codes so it doesn't throw a code.

[Mechie3]

Now my donor harness includes terminals for these devices, but, is it possible they are not necessary? Also, is it true that I can eliminate the "keyless Entry unit" and all associated wires to source? And, what is the "CRU" unit?

Not sure what the CRU unit is.

The solenoids and pressure sensor are because the fuel tank is a closed system. When filling, the ECU will open the solenoid to the charcoal canister to vent pressure to allow it to be filled. It will also pull vapors from the canister into the motor during operation. The FFR tank is a permanently open vent system (unless the car tips, it closes). Unless you want to retrofit the pressure sensor and replace the valve, it's not needed.

You probably can remove the keyless entry, but it might be a pain to do if you have an immobilizer. Subaru doesn't typically release info on what their modules do. They're are (literally) black boxes. Wires go in, wires go out, unless you characterize it yourself you don't really know what type of signal it has and when.

[tmoretta]

From one of my posts on another build thread regarding the fuel pump controller:


It is a voltage regulator that can drop the appx fuel pump duty cycle from 0%, 33%, 66%, or 100% based on what the ecu is demanding.
If you were to datalog what voltage your pump is seeing you might see it go from 5v-14v's
It will also kill the pump if the engine stalls, something that doesn't happen if you just run the pump off a relay.

Car will run fine if you hard wire the pump, but you'd probably want to tune as you will most likely be running rich. It's there, and already wired and a nice safety feature. I'd use it.


As far as the emissions/evap stuff, The pressure control solenoid valve, the drain valve, and the fuel tank pressure sensor, can all be removed, you'll just need to disable the codes so it doesn't throw a code.

Thankyou for the info.