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Discussion Starter · #1 · (Edited)
Ok so I need help, it’s the common fuel solenoid issue but way more complicated.
I just bought this tractor and after some investigation I found someone had bypassed all the safeties, modified the fuel control solenoid, and damaged the injection pump. So the past week has been me repairing everything they destroyed. New K3 relay, new relay socket, new solenoid, new thermistor. Now I have power on 302C red “hold circuit” going to the solenoid, but nothing on the white wire “pull circuit”. Now I’ve studied the wiring diagram for hours, it’s all hooked up right. So what I can figure out is how is the K3 relay energized? Do I have a defective solenoid and the hot should be coming from both red and white? Is there a power feed that just isn’t shown on the wiring diagram?
788113
788114
 

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JD 455, 4610, 4052R, and 6120E
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Now I’ve studied the wiring diagram for hours, it’s all hooked up right. So what I can figure out is how is the K3 relay energized?
You appear to have a technical manual. In the "Theory and Diagnosis" section under "Fuel Supply Circuit Operation", what does it say about the function of the thermistor?

I have a 4610 which doesn't use a thermistor in this circuit, and I have asked before on this forum what the technical manual for a 4300/4400 says about the function of the thermistor, and so far no one has replied with this information.

It would appear from the schematic that when the key is first turned ON, the thermistor passes current to ground through K3 relay contact 87A and allows the fuel solenoid pull-in coil to operate. After a period of time, the thermistor lowers this current to keep from burning up the solenoid pull-in coil. The hold-in coil remains energized to keep the fuel solenoid retracted. This is just a guess how the thermistor works in this circuit without reading more in the 4400 technical manual which I don't have.
 

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I have both North American and European schematics, no difference in that area I just happened to take a picture of the European
OK. Thanks.
In you diagram, I did not see where K3 relay got it's ground. I think what JD Driver posted is good information.(y)
 

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Do I have a defective solenoid and the hot should be coming from both red and white?
You can check the solenoid with a multimeter. The power comes into terminal A and then passes through the pull-in coil to terminal B and the hold-in coil to terminal C. The B,C terminals are grounded to activate the specific coil when needed by the fuel solenoid control circuit. A burned out pull-in coil would probably show infinite resistance between terminals A and B, or a short to case ground.

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Discussion Starter · #9 ·
You appear to have a technical manual. In the "Theory and Diagnosis" section under "Fuel Supply Circuit Operation", what does it say about the function of the thermistor?

I have a 4610 which doesn't use a thermistor in this circuit, and I have asked before on this forum what the technical manual for a 4300/4400 says about the function of the thermistor, and so far no one has replied with this information.

It would appear from the schematic that when the key is first turned ON, the thermistor passes current to ground through K3 relay contact 87A and allows the fuel solenoid pull-in coil to operate. After a period of time, the thermistor lowers this current to keep from burning up the solenoid pull-in coil. The hold-in coil remains energized to keep the fuel solenoid retracted. This is just a guess how the thermistor works in this circuit without reading more in the 4400 technical manual which I don't have.
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You are correct and I understand the theory of operation but I can’t seem to get power to the relay. I’m thinking the solenoid is defective, power should be coming in the red wire the out the white to the k3 relay.
 

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OK. Thanks.
In you diagram, I did not see where K3 relay got it's ground. I think what JD Driver posted is good information.(y)
The ground for K3 runs from K3 85 to K2 85 to V1 7 to frame ground.
 
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Ok so I need help, it’s the common fuel solenoid issue but way more complicated.
I just bought this tractor and after some investigation I found someone had bypassed all the safeties, modified the fuel control solenoid, and damaged the injection pump. So the past week has been me repairing everything they destroyed. New K3 relay, new relay socket, new solenoid, new thermistor. Now I have power on 302C red “hold circuit” going to the solenoid, but nothing on the white wire “pull circuit”. Now I’ve studied the wiring diagram for hours, it’s all hooked up right. So what I can figure out is how is the K3 relay energized? Do I have a defective solenoid and the hot should be coming from both red and white? Is there a power feed that just isn’t shown on the wiring diagram? View attachment 788113 View attachment 788114
K3 is energized by current from the fuel solenoid pull in coil. Red 302C is current into the Fuel solenoid, white 329A is current out from the pull in coil to K#
 

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Discussion Starter · #13 ·
You can check the solenoid with a multimeter. The power comes into terminal A and then passes through the pull-in coil to terminal B and the hold-in coil to terminal C. The B,C terminals are grounded to activate the specific coil when needed by the fuel solenoid control circuit. A burned out pull-in coil would probably show infinite resistance between terminals A and B, or a short to case ground.

View attachment 788128
A to C is 23.9 ohms and A to B is .4 Ohms
 

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You are correct and I understand the theory of operation but I can’t seem to get power to the relay. I’m thinking the solenoid is defective, power should be coming in the red wire the out the white to the k3 relay.
Thank you for this information. It is very helpful to understand the function the thermistor performs in this circuit. The K3 relay coil is initially un-powered, and then as the thermistor heats up (and the variable resistance increases), the K3 relay coil is energized which switches the pull-in coil leg to an open terminal on the relay (87), which removes power from the pull-in coil to keep it from overheating.

The resistances you measured of the two fuel solenoid coils are consistent with what I see on my tractor, and the solenoid works fine even though the hold-in coil resistance is higher than JD shows in the technical manual.

When you turn the key switch from OFF to ON, do you hear a loud clunk as the pull-in coil retracts the fuel solenoid?

If not, what happens if you turn the key the key to ON, then briefly short across the 2 thermistor legs? Does this cause the loud clunk to occur as the fuel solenoid pull-in coil is activated?

Alternately, you could remove the K3 relay and temporarily install a button across relay terminals 30 and 85 to allow you to manually actuate the pull-in coil (push button briefly) after the key switch is turned on. If this activates the pull-in coil and allows the tractor to start, then we can further isolate the problem.

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788139
 

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Discussion Starter · #15 ·
Thank you for this information. It is very helpful to understand the function the thermistor performs in this circuit. The K3 relay coil is initially un-powered, and then as the thermistor heats up (and the variable resistance increases), the K3 relay coil is energized which switches the pull-in coil leg to an open terminal on the relay (87), which removes power from the pull-in coil to keep it from overheating.

The resistances you measured of the two fuel solenoid coils are consistent with what I see on my tractor, and the solenoid works fine even though the hold-in coil resistance is higher than JD shows in the technical manual.

When you turn the key switch from OFF to ON, do you hear a loud clunk as the pull-in coil retracts the fuel solenoid?

If not, what happens if you turn the key the key to ON, then briefly short across the 2 thermistor legs? Does this cause the loud clunk to occur as the fuel solenoid pull-in coil is activated?

Alternately, you could remove the K3 relay and temporarily install a button across relay terminals 30 and 85 to allow you to manually actuate the pull-in coil (push button briefly) after the key switch is turned on. If this activates the pull-in coil and allows the tractor to start, then we can further isolate the problem.

View attachment 788138
View attachment 788139
Turn the key on, no click. Jumper thermistor no click. The only way I get it to work is to apply a 12v source to either 30 or 86.
 

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Turn the key on, no click. Jumper thermistor no click. The only way I get it to work is to apply a 12v source to either 30 or 86.
Ok, thanks. If you unplug the fuel solenoid, turn the key to ON, and then measure the voltage on terminal A (on the tractor side fuel solenoid connector), do you see tractor battery voltage? Terminal A is the common voltage input to both fuel solenoid coils, and voltage should always be present when the key is turned on unless there is a safety interlock open in your tractor.

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The K4 engine run relay provides power to the A terminal of the fuel solenoid relay, if the K4 relay is functional and activated.

Do you have a Power Reverser Transmission (PRT) or hydrostat (HST)? These tractors have different safety interlock requirements, but to be safe, I would be on the seat with the transmission in neutral, the parking brake on, and the PTO off before trying to activate the fuel solenoid.

You will need a good rear PTO switch (which passes power through in the off position) for this to work. On another thread, there was a person who had a bad PTO switch that wasn't properly passing power to the interlock system in the OFF position which was keeping his tractor from starting.
 

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Discussion Starter · #20 ·
I’m about to make some jumpers to go for the solenoid plug, leaving white open so I can see if voltage is coming out of the white terminal on the solenoid side.
 
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