Thanks to anyone offering help with my question, first.

So I have replaced my left and right side fuel pumps during a clutch change project. I got everything back together and figured I would check to make sure everything works as designed before moving on to putting the drivetrain back in the car. So I fill the tanks to full with gas cans, removed the shrader valve from the fuel rail, put a jumper between 87 and 30 on the fuel relay, and began draining the tanks. Both sending units seem to be find and the fuel gauge read full.

When I put power back to the car, the fuel pump started and all seemed fine, until the fuel gauge got to exactly half tank. I found the left tank drained, but did not siphon the right tank at all. I had a bitch of a time getting the fuel lines routed and attached to the left fuel pump, so I assumed I had kinked a line or something. Today I pulled both tanks out of the car and removed the fuel pumps to make sure everything was kosher. I put the fuel system back together and put about 13 gallons in. I attached my Tech2 to the car and found the voltage on the right side was a 1.57v, and did not move while pumping gas out of the fuel rail. The left side continually lowered from 2.49v to below 1v when I stopped. So I can assumed the left side is not siphoning fuel from the right tank.

So my question is, when I jump 87 to 30 at the relay, is there a reason the right side tank would not get reference voltage and not siphon? I have yet to check the pin at the pump and am struggling to find a pinout diagram that makes sense and explains what I should look for.

Thanks for any help or input!

 

So while doing more reading, it seems the jet pump will not siphon fuel to the left tank unless there is adequate fuel pressure. So with the schrader valve out and an open fuel line there is likely only a few pounds of fuel pressure at best I would assume.

Any knowledgeable folks have thoughts on maybe this being the cause?

 

Bumping this up

 

Don’t know what you mean by “reference voltage” as far as jumping 87 and 30...there is no pump in the right tank that pumps fuel over to the left tank !!...some pressurized fuel from the left tank goes to a siphon jet pump in the right tank which creates a venturi to draw fuel from the right tank and then sends it to the left tank...nothing electrical or mechanical with this !!

 

I was hoping someone with your knowledge would respond and answer my question. Thanks for jumping in..... Although your punctuation seems excessive! Haha.

Anyway, while trying to find pin out diagrams to see what was included in the passenger side wiring harness, it appeared there was a 5v reference voltage carried in the grey / black wire of the right fuel tank harness based on information in another thread, which I assume is part of the fuel tank pressure sensor. I then wondered if only jumping 87 to 30 at the relay may have left that harness without energy.

I have become intimately familiar with the concept of the fuel delivery at this point unfortunately. This is the first part of the project that presented any challenges, but it too will be conquered. So I take it you are saying there is no electrical effect on the which jet siphon pump (that is not a pump) which would affect operation. That's what I needed to hear and understand.

 

if the right tank fuel level did not move, the check engine light should be on.

the only electrics on the right tank pertains to fuel level

what pressure were u pumping fuel out of the left tank at?

i suspect the internal lines inside the crossover tube were not connected properly

 

Jumping pins 87 and 30 at the fuel pump relay only turns on the fuel pump...the fuel tank pressure sensor is a whole different system and yes there is a 5 volt reference on that circuit...one of MANY on the car !!

 

Yes, the siphon pump setup is all mechanical. There is nothing electrical to switch on to get it to siphon besides having the fuel pump running.

I have always believed it was excess return fuel from the regulator that went through the jet pump, so dumping fuel from the valve wouldn't allow it to work. If you still have the left mostly empty and the right full then put the valve back in and run the pump for a while and see if the right gets pumped over to the left.

Generally speaking, the siphon pump moves fuel faster than the engine can use it, so it will keep pumping fuel to the left tank until the right is empty first.

 

Happy to say I have decreasing voltage in the right tank and I can see the transfer of the fuel to the left on the voltage​​​​​​, as it will fluctuate in the thousandths as the fuel is transferred.




I hate creating false crisis out of ignorance. But I can confidently say I am much more familiar with how this fuel system works and the installation! I wish that weren't the case.

Thanks for the replies fellas, this forum is great as always.