JD 6400 - InTank Fuel Transfer Pump Electrical Circuit Issue

[landrand]

I'm having issues with my in-tank transfer fuel pump working. I installed a new fuel pump/sender unit in the tank. I put in a new fuel filter replaced the fuel lines. The pump has a forward and return fuel line. I opened the filter bleed screw and when I turn on the ignition to prime the fuel system, the pump turns on for a second and then stops.

There's three wires going to the Fuel transfer pump/sending unit. Ground, DC+ to pump, and a wire for the fuel gage. One of the wires measurs 7.2V and I believe this wire is for the fuel gage.

When I turn the ignition key on, the DC+ wire to the fuel pump measures 12V for a second and then the voltage jumps down to a very low voltage and the pump stops. I took off the hoses to the pump, and the pump did pump fuel for a second and then stopped, as expected by my voltage measurements at the connector.

I called JD service, and they gave me a little info about the circuit, but I'm not sure it is correct for my tractor. Anyway, I attached diagram as to what I THINK the circuit looks like.

Here's a list of items I've done to troubleshoot.

1. I used several of the Bosch Relays in the panel and in the fuel pump circuit. I get the same results and measurements, so the relay appears to be ok.

2. I did a continuity check on the ignition key switch. Everything tests out fine.

3. The fuse F101 is fine as it powers up many other circuits in the tractor.

4. I took the K108 Fuel Pump Relay out and did some voltage measurements in the fuse box with the ignition switch on. I stuck the red multimeter prove into the holes with black probe connected to ground. Here's what I measured with the ignition key on.

Pin 5= 12V
Pin 4= 0V
Pin 3= Varies from 0 to 2.5V
Pin 2= Varies from 1 to 3V
Pin 1= 0V

Something seams weird with these measurements. Without a relay in the socket, why am I getting 12V on pin 5.

In addition, the coil terminals in the relay are show a varying voltage of 1 to 3V. This coil in the relay should be supplied with 12V when the ignition key is on so the relay can provide power to pin 5 and to the fuel pump.

Any idea's what to test out next, opinions, or recommendations. The relay may be wired differently than what I show in my drawing. Any help would be greatly appreciated!

 

[ljjhouser]

Seems to me if the Battery is ok.....and the feed at the fuse (both in and out are
+12)....and you have +12 at the ignition switch both in and out when keyed on......And...wait...Pin 1 is 0 and Pin 3 is 0-2.5v?? HOW can the pump get 12v? The only input to the relay seems to be pins 1 &3.
If the ig switch works, then pin one should read +12. Is the pump trying to work at 2.5v then dropping out.

The path from the battery to pump seems to be from the battery to pin 1 and all should be 12V unless I misunderstood something.

Maybe poor connecting ig switch. Maybe it is not carrying the needed v or current when the pump puts a load on it.

 

[landrand]

Seems to me if the Battery is ok.....and the feed at the fuse (both in and out are
+12)....and you have +12 at the ignition switch both in and out when keyed on......And...wait...Pin 1 is 0 and Pin 3 is 0-2.5v?? HOW can the pump get 12v? The only input to the relay seems to be pins 1 &3.
If the ig switch works, then pin one should read +12. Is the pump trying to work at 2.5v then dropping out.

The path from the battery to pump seems to be from the battery to pin 1 and all should be 12V unless I misunderstood something.

Maybe poor connecting ig switch. Maybe it is not carrying the needed v or current when the pump puts a load on it.

I've done some tests and rethinking the circuit design. Here's an updated version of the fuel pump circuit design and a few tests to verify. I believe this one is correct, but I need to do a few more voltage measurements to vallidate.

 

[K5lwq]

This is how it should be wired.

Measure voltage using pin 30 and chassis ground. Should see 12v with key off. If not, trace 30 wire back to battery source.

Measure voltage using pin 86 and chassis ground with key in on position. Should see 12v. If not trace 86 wire back to switch and test.

Measure voltage using pin 86 and pin 85 with key on. Should see 12v if not and assuming 86 to chassis ground was good then trace wire 85 back to ground.

Pin 87 to chassis ground should read 12v with relay installed and key on.
Hope this helps.