John Deere 6400- Troubleshooting In-tank Fuel Transfer Pump Circuit

[landrand]

My John Deere 6400 (Product ID# L06400v131378) has been sitting in the garage for 5 years with no use. I am now taking the necessary steps to get it back in running condition.

1. I drained the fuel tank and put in 5 gallons of fresh diesel fuel.
2. I changed the fuel filter.

Unfortunately, I was not able to get the tractor to start. When troubleshooting the issue, I discovered my in-tank fuel transfer pump was not pumping fuel to the fuel filter when I turned the ignition key to on.

I removed the in-tank fuel transfer pump and tested it with a 12V battery. The pump was bad and I am preparing to replace it with a new pump/sending unit and new fuel lines.

When testing the wires to the sending unit/pump (with the ignition key on) I'm only getting 7.2V. I'm a novice to fuel transfer pumps so I did a little research. I read that fuel pumps often use various changes in voltage to control the flow of fuel. I suspect it should be 12V but am not sure. Have a couple of questions for the guru's:

1. Should the voltage to the pump/sending unit be a full 12V when the ignition key is on?

2. If 7.2V is low, I need to troubleshoot the circuit for a high resistance. I don't have the circuit wiring diagram but I suspect the ignition key switch, and fuse F101 Main Switch (Term BAT) are part of the circuit. Would anyone have a wiring diagram or information where I should begin troubleshooting this circuit with an multimeter?

Any advice/recommendations to this issue would be greatly appreciated!

 

[MTGreen]

It's a DC motor so lower voltage just means slower speed and there's a return line so the pump is set up to provide more fuel than the injection pump can use.
If it were me I would wait until I get the new pump installed and tested before diving in to the wiring here. 7.5v to me is not necessarily a smoking gun -maybe add some dielectric grease to the connectors and relay feeding it, then make sure your grounds are good

 

[landrand]

It's a DC motor so lower voltage just means slower speed and there's a return line so the pump is set up to provide more fuel than the injection pump can use.
If it were me I would wait until I get the new pump installed and tested before diving in to the wiring here. 7.5v to me is not necessarily a smoking gun -maybe add some dielectric grease to the connectors and relay feeding it, then make sure your grounds are good

Today, I installed the pump and reconnected the wiring. When i turn the ignition key on, the pump momentarily starts then stops. There something funny going on with the circuit.

 

[MTGreen]

Today, I installed the pump and reconnected the wiring. When i turn the ignition key on, the pump momentarily starts then stops. There something funny going on with the circuit.

Did it run continuously before or is it a pressure sensitive pump that shuts off when it gets to pressure?

 

[landrand]

Did it run continuously before or is it a pressure sensitive pump that shuts off when it gets to pressure?

To be truthful, I didn't know the tractor had an in-tank transfer fuel pump until a week ago when I started to troubleshoot why it wouldn't start. After draining the old fuel, putting in fresh diesel and changing the fuel filter, I figured out there was an issue with either the pump/sending unit or perhaps the circuit. I removed the pump and tested it with 12V and it would'nt start. The old in-tank transfer pump was bad and the sending unit wires were in bad shape upon inspection.

Now that I have a new pump/sending unit and fuel lines, I'm trying to prime the fuel system. I open the air bleeding screw on the fuel filter, turn on the ignition switch, and watch for fuel to come out of the bleed screw. I haven't seen any fuel come out of the fuel filter bleeding screw yet. I can hear the pump start when I turn on the ignition, but it only comes on for a second or two and then stops. I checked the voltage at the pump and it stays at 7.2V while the key is in the on position, yet the pump stops after a second or two. Perhaps, the fuel filter is full of fuel and the pump shuts off when it gets to pressure. Tomorrow I'll check to see if the fuel filter has any fuel in it. Thanks for your help!

 

[MTGreen]

May consider taking the hose off of the fuel filter assembly and putting it down below the level of the fuel tank to make sure you don't have any obstructions and your line is full of fuel before hooking it back up to the filter assembly

 

[landrand]

May consider taking the hose off of the fuel filter assembly and putting it down below the level of the fuel tank to make sure you don't have any obstructions and your line is full of fuel before hooking it back up to the filter assembly

Ok. I'll do this tomorrow! Thanks for the help!