Dual Lift Pumps with Dual Tanks ?

[Acesneights1]

Was trying to help someone out one another site I belong to and this is a first to me. He is describing that he has two tanks and two lift pumps ? I am thinking he is looking at switching valves but I have never worked on a 6.5 truck with dual tanks.

Here is his post :


How does the rear lift pump work on a 2000 chev. 3500 with two tanks. Truck is only running on the front tank and will pump about 4 gallons from the rear tank. We replaced the rear lp about 2 weeks ago and it will pump when the key is turned on. Does the rear lp pump into the front tank? The front pump seems to work fine. Thanks

 

[Turbine Doc]

Invite him to come here to post, always easier to troubleshoot 1st hand rather than via a proxy.

Never seen a dual lift setup either, pics of what he has would be handy, must have some sort of switching circuit that should power the 2nd lift when the changeover vale to 2nd tank is selected.

Gnds, would be my 1st guess, ought to be a simple check, start truck and read for volts at lift pump connector, truck should stay running with no lift, and is the change over valve actually shifting over

 

[buddy]

Ask Matt Bachand, I think he has dual lift pump with stock dual tanks.

 

[Acesneights1]

Never saw that wasn't sure it existed.
Yeah guess I'll invite hm over. I spend alot of time in the heavy truck section on that site.

 

[MRB 6.5TD]

Ask Matt Bachand, I think he has dual lift pump with stock dual tanks.

I sure do. Uses different rear FSU and has an exact stock replacement liftpump that pumps from the rear tank to the front tank.

The front tank then pumps the fuel to the IP obvoiusly.

the 2nd LP must be run off the float of the rear tanks FSU is what i've come to believe. Here is my question that havn't been able to answer yet, as it seems not many people talk about this dual configuration i've noticed so I'm jumpin all over it.

When you fill the front tank, and the rear tank (PO told me to do it that way FWIW) what stops the the rear tank from pumping too much fuel into the front tank?

 

[MRB 6.5TD]

Invite him to come here to post, always easier to troubleshoot 1st hand rather than via a proxy.

Never seen a dual lift setup either, pics of what he has would be handy, must have some sort of switching circuit that should power the 2nd lift when the changeover vale to 2nd tank is selected.

Gnds, would be my 1st guess, ought to be a simple check, start truck and read for volts at lift pump connector, truck should stay running with no lift, and is the change over valve actually shifting over

There is no switch to change tanks, the rear pumps to the front tank.

 

[NVW]

The rear pump must only work when the front tank fsu is below a certain level would be my guess

Leo

 

[MRB 6.5TD]

The rear pump must only work when the front tank fsu is below a certain level would be my guess

Leo

I was thinking the same thing. I took a nice picture of my rear LP but somehow it got lost before making it from inside the trucks ass to the computer I'll go crawl back up there and take another picture.

 

[MRB 6.5TD]

If i hold my breath I can squeeze my torso between the rear tank and bumper allowing me plenty of work room to change either FSU. I need to drop the front driveshaft to access the front. Here some pix

The camera is sitting dead over the rear tank & FSU taking these pictures for reference. The rear tank is a square shaped that sits right behind the rear pumpkin.

 

[diesel65]

The dual tank trucks have as you know two lift pumps and two sending units, To control the system the PCM controls the primary pump as if it was a single tank system, the secondary pump is controlled by a fuel balance relay and fuel balance module.
The module has two functions, one is to combine the two tank sending units resistance readings and create an output signal to the instrument cluster for proper guage reading.
The second function is to energize the balance relay when the primary tank is two gallons lower than the secondary tank.
The module and the relay is located inside the frame rail under the drivers seat.
I have a few trucks where I work and have noticed when this system is not working, the problem is usually a bad secondary tank sending unit.

 

[MRB 6.5TD]

Was trying to help someone out one another site I belong to and this is a first to me. He is describing that he has two tanks and two lift pumps ? I am thinking he is looking at switching valves but I have never worked on a 6.5 truck with dual tanks.

Here is his post :


How does the rear lift pump work on a 2000 chev. 3500 with two tanks. Truck is only running on the front tank and will pump about 4 gallons from the rear tank. We replaced the rear lp about 2 weeks ago and it will pump when the key is turned on. Does the rear lp pump into the front tank? The front pump seems to work fine. Thanks

His rear FSU is probably garbage Aces...