ECM B fuse pops when I switch fuel tanks...

[johnnydefacto]

Both were working perfectly until today, went to switch fuel tanks to left side and the ecm-b fuse popped. It kept popping when I would key the ignition until I switched back to right side tank. Then it worked fine. Every time I switch to left tank it pops.

Leaving on a trip in 10 days so I have limited time to get this thing right. First thing that comes to mind is the fuel pump on that side went bad. Other than that trying to chase down wires from the cab to the pump is going to be tough because the wires are all tied up on the frame in the loom.

Where should I start? how do I take the fuel pump out of the system to check the switch to see if the fuse pops?

thank you

 

[chengny]

Where should I start? how do I take the fuel pump out of the system to check the switch to see if the fuse pops?


You might be best off if you cut the wire as near to the tank as possible. If the fuse holds when power is applied- it's the pump. If it blows - the problem is in the dash switch, the transfer valve or the interconnected wiring. It won't be in tank level sensing circuit, that is separate from the power for the pump and the motorized valve.

Ideally, all the wiring, the dash switch and the transfer valve motor could be eliminated if the harness was able to be disconnected at the sender. But unless your bed is off, that's probably not going to happen. You might want to find the best place to work and cut the wire there. If you do it in an accessible spot it will be easy to make a splice after the problem is fixed.

One thing you can do is eliminate the entire transfer valve just by unplugging the connector from the Pollak valve. Power will still go to the LH fuel pump because the pump feed is branched off from the tan wire before it goes into the valve. The tank won't be lined up to the fuel system - and the level will be wrong - but it will just be for the time it takes to do the test.

You must be registered for see images attach

Another way to confirm that the problem is in the fuel pump would be to check the resistance of it's motor windings. Use a multimeter and attach one probe to a good clean spot on the frame. The other probe needs to make contact with the conductors inside the insulation of the tan wire. You can make contact with the copper by cutting a tiny slice in the insulation with a utility knife - or poke through the insulation with the point of the probe. With the meter in the auto position - or the lowest ohm setting - measure the resistance of the motor windings.

This isn't an exact science. What you are looking for is a dead ground or a short in the windings either of which will be indicated by a reading of 0 ohms. Any reading above 1 ohm on the meter means the motor is not short circuited or shorted to ground.

Rule of thumb:

0 resistance = Bad fuel pump (winding are shorted or grounded)
1-3 ohms = Good fuel pump
High resistance = Bad fuel pump (open in the windings)

 

[johnnydefacto]

Where should I start? how do I take the fuel pump out of the system to check the switch to see if the fuse pops?


You might be best off if you cut the wire as near to the tank as possible. If the fuse holds when power is applied- it's the pump. If it blows - the problem is in the dash switch, the transfer valve or the interconnected wiring. It won't be in tank level sensing circuit, that is separate from the power for the pump and the motorized valve.

Ideally, all the wiring, the dash switch and the transfer valve motor could be eliminated if the harness was able to be disconnected at the sender. But unless your bed is off, that's probably not going to happen. You might want to find the best place to work and cut the wire there. If you do it in an accessible spot it will be easy to make a splice after the problem is fixed.

One thing you can do is eliminate the entire transfer valve just by unplugging the connector from the Pollak valve. Power will still go to the LH fuel pump because the pump feed is branched off from the tan wire before it goes into the valve. The tank won't be lined up to the fuel system - and the level will be wrong - but it will just be for the time it takes to do the test.

You must be registered for see images attach

Another way to confirm that the problem is in the fuel pump would be to check the resistance of it's motor windings. Use a multimeter and attach one probe to a good clean spot on the frame. The other probe needs to make contact with the conductors inside the insulation of the tan wire. You can make contact with the copper by cutting a tiny slice in the insulation with a utility knife - or poke through the insulation with the point of the probe. With the meter in the auto position - or the lowest ohm setting - measure the resistance of the motor windings.

This isn't an exact science. What you are looking for is a dead ground or a short in the windings either of which will be indicated by a reading of 0 ohms. Any reading above 1 ohm on the meter means the motor is not short circuited or shorted to ground.

Rule of thumb:

0 resistance = Bad fuel pump (winding are shorted or grounded)
1-3 ohms = Good fuel pump
High resistance = Bad fuel pump (open in the windings)

okay, thank you. I will try these tests out...

 

[johnnydefacto]

Where should I start? how do I take the fuel pump out of the system to check the switch to see if the fuse pops?


You might be best off if you cut the wire as near to the tank as possible. If the fuse holds when power is applied- it's the pump. If it blows - the problem is in the dash switch, the transfer valve or the interconnected wiring. It won't be in tank level sensing circuit, that is separate from the power for the pump and the motorized valve.

Ideally, all the wiring, the dash switch and the transfer valve motor could be eliminated if the harness was able to be disconnected at the sender. But unless your bed is off, that's probably not going to happen. You might want to find the best place to work and cut the wire there. If you do it in an accessible spot it will be easy to make a splice after the problem is fixed.

One thing you can do is eliminate the entire transfer valve just by unplugging the connector from the Pollak valve. Power will still go to the LH fuel pump because the pump feed is branched off from the tan wire before it goes into the valve. The tank won't be lined up to the fuel system - and the level will be wrong - but it will just be for the time it takes to do the test.

You must be registered for see images attach

Another way to confirm that the problem is in the fuel pump would be to check the resistance of it's motor windings. Use a multimeter and attach one probe to a good clean spot on the frame. The other probe needs to make contact with the conductors inside the insulation of the tan wire. You can make contact with the copper by cutting a tiny slice in the insulation with a utility knife - or poke through the insulation with the point of the probe. With the meter in the auto position - or the lowest ohm setting - measure the resistance of the motor windings.

This isn't an exact science. What you are looking for is a dead ground or a short in the windings either of which will be indicated by a reading of 0 ohms. Any reading above 1 ohm on the meter means the motor is not short circuited or shorted to ground.

Rule of thumb:

0 resistance = Bad fuel pump (winding are shorted or grounded)
1-3 ohms = Good fuel pump
High resistance = Bad fuel pump (open in the windings)

Okay I disconnected the fuel pump and the fuse pops still.

So now I am going to bypass the selector switch...

 

[johnnydefacto]

Where should I start? how do I take the fuel pump out of the system to check the switch to see if the fuse pops?


You might be best off if you cut the wire as near to the tank as possible. If the fuse holds when power is applied- it's the pump. If it blows - the problem is in the dash switch, the transfer valve or the interconnected wiring. It won't be in tank level sensing circuit, that is separate from the power for the pump and the motorized valve.

Ideally, all the wiring, the dash switch and the transfer valve motor could be eliminated if the harness was able to be disconnected at the sender. But unless your bed is off, that's probably not going to happen. You might want to find the best place to work and cut the wire there. If you do it in an accessible spot it will be easy to make a splice after the problem is fixed.

One thing you can do is eliminate the entire transfer valve just by unplugging the connector from the Pollak valve. Power will still go to the LH fuel pump because the pump feed is branched off from the tan wire before it goes into the valve. The tank won't be lined up to the fuel system - and the level will be wrong - but it will just be for the time it takes to do the test.

You must be registered for see images attach

Another way to confirm that the problem is in the fuel pump would be to check the resistance of it's motor windings. Use a multimeter and attach one probe to a good clean spot on the frame. The other probe needs to make contact with the conductors inside the insulation of the tan wire. You can make contact with the copper by cutting a tiny slice in the insulation with a utility knife - or poke through the insulation with the point of the probe. With the meter in the auto position - or the lowest ohm setting - measure the resistance of the motor windings.

This isn't an exact science. What you are looking for is a dead ground or a short in the windings either of which will be indicated by a reading of 0 ohms. Any reading above 1 ohm on the meter means the motor is not short circuited or shorted to ground.

Rule of thumb:

0 resistance = Bad fuel pump (winding are shorted or grounded)
1-3 ohms = Good fuel pump
High resistance = Bad fuel pump (open in the windings)

I cut the fuel pump wires and the fuse did not pop this time. So I ordered a whole new pump/sending unit assembly. I do not know what 2 wires I cut yesterday, I think they went to the transfer valve... going to have to splice those back together when I pull the bed off to change pumps.