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JHoop
JHoop, Chevy Technician
Category: Chevy
Satisfied Customers: 5446
Experience:  14 Year Engine Builder,16 years as a Tech HvyLine, Suspension, Electrical, Brakes, 6 Year Shop Owner
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I have a 1998 chevy 3500hd truck that has a fuel system problem.

Customer Question

I have a 1998 chevy 3500hd truck that has a fuel system problem. It is a dual Tank system. the gauge is always on E. The truck runs out of gas when the front tank empties. ( front tank empty - rear tank full )
Submitted: 5 years ago.
Category: Chevy
Expert:  JHoop replied 5 years ago.
Hello John, my name isXXXXX you for choosing justanswer.com. I uploaded the procedure in .pdf format here to justanswer. You can download it by clicking HERE and HERE. I hope this helps you. If you have any more questions or need any more diagrams, please don't hesisitate to ask...Thanks again, JHoop
Expert:  JHoop replied 5 years ago.
Fii all the wiring has been checked, the fuel pump balance module is faulty. I uploaded the procedure in .pdf format here to justanswer. You can download it by clicking HERE. I hope this helps you. If you have any more questions or need any more diagrams, please don't hesisitate to ask...Thanks again, JHoop
Customer: replied 5 years ago.
Hello JHOOP is there any way we can check the relay, or is it a buy and try type of thing Thanks, John
Expert:  JHoop replied 5 years ago.
It is not the relay that is the problem. The fuel pump balance module is the problem. The only way to test these is with a factory scanner. If you have any more questions or need any diagrams, please dont hesisitate to ask...Thanks again, JHoop
Customer: replied 5 years ago.
I put on the new module. Fuel gauge still reads E ( although it does pop all the way to the right and then back when i first turn the key) I can't tell if the transfer pump is working because both tanks are full. PLEASE ADVISE
Expert:  JHoop replied 5 years ago.
When the engine is runnimg, can you hear the rear pump run with the gas cap off?
Customer: replied 5 years ago.

I can try that but, will the transfer pump run with both tanks full ?

Should i first siphon 5-10 gals out of the front tank???

Expert:  JHoop replied 5 years ago.
The treansfer pump will run. It is a lower pressure pump,. and is contreolled by the transfer module. It is very possible that the rear pump failked, drawing too many amps, and blew the module out. You should hear the pump run in the rear, when the key is switched to run for 2 seconds. If not, the pump has failed, taking out the module with it.
Customer: replied 5 years ago.

I don't think there is a pump in the rear tank. The rear tank has a brand new sending unit in it.

When I turn the key on (w/o turning the engine over) I can hear the pump ( that i believe is in th efront tank)run for a couple seconds. then it stops

Customer: replied 5 years ago.
Did you get my last reply
Expert:  JHoop replied 5 years ago.
There is a slave pump ion the rear tank. Read the description and operation of the system. It is in the first .pdf file I posted. It is still there for you to download.
Customer: replied 5 years ago.

The way i understand the written description is: Main fuel pump/sending unit is in the front (or main ) tank. Then there is a transfer pump to tranfer fuel from the rear (or aux )

tank to the front tank. The transfer pump is not in the rear tank, it's on the frame rail between the 2 tanks. are you saying there is another pump in the rear tank that is not part of the sending unit ?

Expert:  JHoop replied 5 years ago.
Iam reffering to the transfer pump. Sorry, i was not clearer in my responce. If you can feel it run with the key in run for 2 seconds, or when the engine is running, then that pump has failed. If you have any more questions or need any diagrams, please dont hesisitate to ask...Thanks again, JHoop
Customer: replied 5 years ago.

OK We got the gauge working-- Transfer pump still not working- we have a new module ( fuel pump balance module). The transfer pump is getting between 6 & 7 Volts w/ the old or the new module-- the gauge came back on with a bad fuse we found (ing E) we have a new transfer pump and it doesn't apper to work either. when we turn the key on the power to the transfer pump only last a couple seconds-- with the truck running it stays on-- we partially emptied the front (main ) tank. are we getting the right voltage ? do we maybe have a new defective pump ?

Expert:  JHoop replied 5 years ago.
The IGN E fuse 10 amp supplies 12v to the balance pump when the module turns it on. There must be 12v to the rear tank pump. Look at the diagram I provided. graphic
Customer: replied 5 years ago.

OK so why do you think i am only getting 6-7 volts? Also I can't tell on the diagrem where it says 12 volts. the pump only has 2 wires so i should be able to activate the pump using the trucks battery--Right? I tried to run the pump directly off the battery and it did not do anything (unless it's really really quite, i even held it to my ear)

so I'm guessing the new pump Napa sent out is defective. What would account for the reduced voltage at the pump ?? relay-- bad wire ??? where do you think i should check first ?

Expert:  JHoop replied 5 years ago.
There are no supply fuses less than 12v. You will have to trace the circuit circled in the diagram, and run a new wire from the IGN E fuse tothe relay. If you have any more questions or need any diagrams, please dont hesisitate to ask...Thanks again, JHoop
JHoop, Chevy Technician
Category: Chevy
Satisfied Customers: 5446
Experience: 14 Year Engine Builder,16 years as a Tech HvyLine, Suspension, Electrical, Brakes, 6 Year Shop Owner
JHoop and 9 other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
Hi J We got it. It turned out that the old pump was shorting out the ign E fuse. and the new pump was just fine. we had chanded that fuse but didn't keep checking it. anyway, it's a long stupid story. THANK YOU !! for your help and patience
Expert:  JHoop replied 5 years ago.
If have any more questions or need any diagrams, please dont hesisitate to ask...Thanks again, JHoop

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