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Need a detailed explanation of RX8 fuel system?

Old 01-12-2019, 03:21 AM
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Need a detailed explanation of RX8 fuel system?

Hello everyone,
I recently bought a rx8 model 2003, and the previous owner has messed with the fuel system which includes issues like:
.getting no fuel indication on speedometer (if there is fuel or not the reserve light is always on and the indication needle is always on empty)
.there is fuel pump wiring on the inside of the tank going to the other side of the tank to run a secondary pump that pumps fuel to the passenger side of the tank.
.the fuel pump assembly on the pessenger side is missing.
.on the driver side of the tank the fuel pump is lying horizontal on the floor of the tank and the assembly portion has a gauge sort of think that has 2 wires going to the inside of the tank.
.there is a return system of sort the excess fuel always go to the driver side of the tank.

What i want to acheive here is to restore all of this mess to company setup!

If someone here can give me detailed information on how the company system is and how it looks that would be highly appreciated!
If someone could add in pictures of the company setup would be great.
😊😊😊


​​​​
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Old 01-12-2019, 07:40 AM
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Stock fuel system is returnless with a pump in the left side of a saddle tank and a venturi pickup in the right side tank that uses the overflow from the fuel pump to activate. There are 2 fuel level sensors...one in each side of the tank that the ECU uses to calculate the fuel level.
There should be a pump assembly in the left tank and a pickup in the right tank... and a black plastic fuel line that connects them and attaches to the pump unit and too the siphon pickup

It sounds like that is all gone.... the easiest thing would likely be to buy a complete tank setup from a wreck... otherwise you will have a difficult time sourcing all of the missing parts.
You may still need to replace the pump unit in a salvage tank though as the filter is integrated into the unit and is not replaceable
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Old 01-12-2019, 07:39 PM
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google mazda RX8 service repair manual may be there
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Old 01-26-2019, 02:02 PM
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Originally Posted by dannobre View Post
Stock fuel system is returnless with a pump in the left side of a saddle tank and a venturi pickup in the right side tank that uses the overflow from the fuel pump to activate. There are 2 fuel level sensors...one in each side of the tank that the ECU uses to calculate the fuel level.
There should be a pump assembly in the left tank and a pickup in the right tank... and a black plastic fuel line that connects them and attaches to the pump unit and too the siphon pickup

It sounds like that is all gone.... the easiest thing would likely be to buy a complete tank setup from a wreck... otherwise you will have a difficult time sourcing all of the missing parts.
You may still need to replace the pump unit in a salvage tank though as the filter is integrated into the unit and is not replaceable
Thank you dannobre for the swift reply, and sorry for responding late i got quite busy with exams and job, now that i am free we can discuss what i found.

1. Couldn't find a complete fuel tank.
2. I bought a N3H1 fuel pump assembly including the pump.
3. Had a close look at the fuel tank and i found out that there is a return which is feeding back fuel into the tank. The plastic pipe that goes out of the siphon of the fuel pump assembly is there, but it was turned other way arround. Now i don't know what you are reffering to as the pick up in the right tank, i couldn't find that.
4. I am planning to keep the return line and install the N3H1 assembly, i also bought mazda 6 fuel pump assembly and i am planning to use the top on the N3H1 so that i could feed the return directly to the pump side. I will also be installing a filter bag on the other side of the black plastic pipe so that it cleans the fuel before sending it to the pump side. Now there is guage sort of a thing installed on the right side its sitting in the fuel pump hole, if its fixed can it measure the fuel level.

​​​​​​Just before i do this, it would be good dannobre if you can point out what i am missing here!
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Old 01-27-2019, 07:12 PM
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There is a fuel level sensor in each side of the tank. If it is disconnected you might have to dig around to look for the small plug that plugs into the lid. The wires are really small and they can break easily. You might have to repair them


The right side of the tank has a lid with a pickup attached that the black tube that crosses over from the left side of the tank attaches to. This is the siphon that transfers fuel from the right to left side of the tank. The black line attaches to the siphon on the fuel pump assembly with a push lock fitting.

If you are going to add another pump to the right tank you will have to figure out how you want to add it to the system. If you just drive the car on the street you will need fine with the siphon assembly if it works properly. If you track the car you might want to change things up a bit.








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Old 01-28-2019, 03:59 PM
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Thank you! Dannobre once again for the reply.
As you said we found the guage wires and both were fixed and i was getting a fuel level feed on the tachometer.
The mazda 6 fuel pump assembly lid was added to the N3H1 and the return pipe was put on it. The only issue i was getting was with the pickup and siphon fuel was not going from the right to left, but thanks to you i found out that i was missing a part that goes on the right side (picture below)

The pick up assembly that attaches to the siphon assembly via black pipe!
i will hopefully look for this part tomorrow.
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Old 01-28-2019, 04:01 PM
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Oh! Here is a picture of the fuel pump assembly i bought.

N3H1
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Old 01-28-2019, 04:03 PM
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Once its all done and successful i will post pictures! So that its helpfull for others aswell!

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Old 01-29-2019, 03:24 PM
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Originally Posted by dannobre View Post
There is a fuel level sensor in each side of the tank. If it is disconnected you might have to dig around to look for the small plug that plugs into the lid. The wires are really small and they can break easily. You might have to repair them


The right side of the tank has a lid with a pickup attached that the black tube that crosses over from the left side of the tank attaches to. This is the siphon that transfers fuel from the right to left side of the tank. The black line attaches to the siphon on the fuel pump assembly with a push lock fitting.

If you are going to add another pump to the right tank you will have to figure out how you want to add it to the system. If you just drive the car on the street you will need fine with the siphon assembly if it works properly. If you track the car you might want to change things up a bit.
Okay dannobre! Everything is in place
Siphon working no spillage from the fuel tank except for the passenger side. The lid does not sit tight on the opening! I will get another one. There is also a slight problem with the guage wiring the feeds are gone again.
There is a fuel pump issue I think: there is missing and sometimes the fuel pump just stops working. It works fine for a while and then the car starts missing. I had to stop and turn the ignition off for 20 mins each time so that the pump could rest. After that's done the pump works fine for a while and then does the same over again.
I would also like to ask 2 questions. If the pump is weak and not creating enough pressure will the siphon work.
​​​​​​can I just leave the black siphon pipe on the other side of the fuel tank disconnected from the pick up assembly will the siphon work then?

It would be good if you add some experience on this issue.
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Old 01-29-2019, 03:31 PM
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It is possible that the black pipe has jammed or torn up the sensor wires again... or when you put the lid on it disconnected the wiring. There is waiting on both sides... and the left side is easy to damage when putting in the pump unit if you aren't careful

The used fuel pump is a bit of a risk. You either need to replace the whole unit ..... best idea. Or replace the pump. Replacing the pump is harder than it sounds...you have to take the unit apart and carefully uncrimp the corrugated fuel line and then reinstall it all with no leaks. The other issue is that the fuel filter is built in and most likely isn't great.

To keep it simple buy a new unit... it will simplify your life a lot. You get a new filter that is good for 100k and a pump that will work well for a stock car
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