^ cutting an 'access' hole would definitely classify as a make work exercise
I did what was possibly the first 80 subtank install in the US on my 80 and that tank has been in and working for 20+ years now. Never had to access the top of the tank and as others have said, dropping it would be very easy if needed. Of course if you have nothing better to do, then go ahead and cut metal and install your never to be used cover
Haha, true. Although it took me all of 5 minutes to take a holesaw to the factory access panel and pop on the cover. I’d wager that’s even easier than dropping the tank. I guess I’m out $15 for the cover though...
Made some progress today replacing the fuel lines on discharge side of the transfer pump. 5/16" fuel injection hose. I also replaced the vapor and return hoses, with 1/4" fuel line, that connect to the main tank. All of these will be difficult to access after the main tank is installed. The suction lines to the transfer pump I will be able to reach from underneath.
I replaced the o-ring on filler neck with new. Part # 96712-24053
Made the wiring harness for dash switch and ran to kick panel. Dash Switch Pinout
1 - Rheostat Ground (will tap into rear heater switch wiring. white/green wire)
2 - +12v switched for backlight (will tap into rear heater switch wiring. green wire)
3 - ECU Pin #5
4 - +12v (gauge pod fuse)
5 - N/A
6 - Ground at kick panel
7 - N/A
8 - N/A
9 - ECU Pin #7
Photo 1 - Harness for dash switch
Photo 2 - new o-ring installed
Photos 3 - How the dual tank valve works. In this position fuel is directed to the main tank. There is a rubber seal that will prevent fuel from entering the sub tank. This is the normal position of the dual filler neck - knob pushed in.
Photo 4 - Filler neck valve in position to fill sub tank. There is no seal on the passage to the main tank. Some fuel will enter the main tank while filling the sub tank. In this position the knob is pulled out. Fill the sub tank first, then the main tank.
Finished the wiring today. Made a similar ID5 connector with all the wires run to it.
The main tank was cut and ring welded on. This will house the 75% level sensor.
I need to verify all the wiring and test the system.
I installed everything and system is functioning as designed. Had a few issues that needed troubleshooting at first attempt. The Sub dash switch diagnostics gave me both error codes #2 (fuel level switch signal open or (main tank) fuel level high) and #6 (fuel level switch open or fuel level high (extra or sub tank)). #2 pertains to the main tank and #6 to the sub tank. The issues are outlined below.
1. Bb1 connector had a rotted pin. This is the connector under the truck where the spare is. It connects to the sub tank level sending unit. My issue was that the ECU would not get a sub tank switch signal. There are two sensors in the sub tank. A level switch and level rheostat (float). The switch is used to tell the ECU if there is more than minimum fuel in the tank. If there is, transfer is permitted. If not, it wont pump. The rheostat is part of the overhead console circuit. It changes the resistance and hence the indication on the overhead gauge. Instead of splicing wires, I noted there were unused pins in the Bb1 connector that also ran to the kick panel. I swapped pin positions in the connector and rewired the new ID5 connector to match this new wire. Typically this is the Y-L wire.
2. The second issue was a bad connection at Bd2. This is the connector under the driver passenger floor board by the frame. The harness penetrates the cab at that point. These connectors see all the road dirt. I cleaned it out as best as I could but one pin was still not making good contact. This pin was connected to the new main tank level sensor that tells the ECU if the tank has more or less than 75% capacity. Without this input the system would not transfer. I stripped an 18gauge multi-strand wire and stuck one of the strands into the female pin. This created the needed contact for signal to transfer. I will consider replacing the pins in the future if I have issues.
- LX450 is not prewired for this system like the Land Cruisers. You have two options: add the pins/wires and connectors or pickup a harness from a part out. I ended up getting a harness from a 3x locked cruiser to fit my LX.
- Use the wiring diagram posted in post #1 and trace out the wires from the ECU to kick panel. Do yourself a favor and take notes on wire colors and pin locations. It has been mentioned before and I can confirm that there are many combinations of harness and wire colors. A multi meter is the best tool for this project.
- The wires you want to trace from the ECU to kick panel are:
-> Pin 2 - power to the fuel pump ECU. You will supply power to this wire from the ECU-B fuse by taping/splicing it.
-> Pin 15 - connection to onboard diagnostics. You will connect this wire to pin 5 of the ABS connector. Photo of this is on page 4 post #77.
-> Pin 5 - connects to the dash switch bulb circuit. ECU will send signal to turn on the switch indication light. This light is used for diagnostics as well so ensure it works.
-> Pin 7 - connects to the dash switch circuit. When you push switch this sends a signal to pin 7 of ECU.
-> Pin 14 - OPTIONAL - connects to cluster charge light circuit. Tells the ECU if battery is low to not run pump. I did not connect this.
-> The last wire that you need to trace is the sub tank level indication that is used for the overhead console. This wire is not found at the ECU but is located under the truck by the spare tire at connector Bb1.
- If possible, replace all fuel hoses with new. The last thing you want to do is have a leak and try to replace the hoses while everything is in the truck.
- Once your main tank is out of the truck, look it over for rust and take care of it then.
- If you are unable to source the new main tank fuel pump assembly, modifying your existing is not very involved. The only difference between the US and those with a sub tank system is one filler tube. You can drill a hole and install a short piece of tube via welding or mechanically fitted.
- There is a lot of information in this thread which can be overwhelming. Read to understand what the objective of the system is and what you are going to have to do to make it work. It's a simple system once you see how it all works and the wiring is pretty straight forward.
Hope this helps the next person doing this upgrade. Total cost in 2020 is about $1500 for this upgrade.