John Deere 4400 hard to start/thermistor maybe?

[ridgerunnerinwv]

Soundguy, the theory behind the thermister is that it takes much more power to retract the solenoid than it does to keep it retracted. To that end, the thermister cuts down the power draw by heating up & restricting power to the solenoid by raising resistance over time.

Ridgerunner, since I cut for a while today I took a couple pics. First is the back of the HP pump showing the bracket that must be unbolted (the throttle linkage passes through it & the fuel filter is mounted to it) behind the shut-off solenoid (that's the gold piece on the back of the pump, yours should be black if it hasn't already been changed). Second is a pic of the thermister. It is about the size of my little finger's nail.

You must unbolt the bracket & (something I forgot to mention) pop the throttle linkage from the pump arm (it prys off) to get to the back solenoid bolt.

Thank you dbdartman,
I will print the pictures for my reference and I am going to order 2 of the thermistors,that way I will have a spare.

 

[dbdartman]

Just wondering if ridgerunner ever got his tractor started.

Well....?

 

[patrick_g]

Soundguy, I too was waiting with baited breath (no I didn't eat anchovies) to find out what the heck the thermistor was for. Oh well, does it simplify the ignitioin switch or what? In the olden days the start position of an automotive ignition switch gave full voltage to the ignition while cranking. Of course full voltage while cranking was probably well under 12 due to heavy draw. Then when you released the key switch it reverted to the "run" position and the current (and voltage) going to the coil was limited by the "ballast" resistor. If a ballast resistor went out the symptom was the car would start but when you turned lose of the key it would immediately die. I suppose the thermistor is in series with the coil exitation current going from the switch to the starter solenoid. Gee, they could have put a lamp socket on the dash and put a tungsten filament bulb in series with the solenoid coil. Tungsten exhibits a non linear temperature dependant resistance with low initial resistance that increases with temperature. This would have given the operator a light that came on when cranking and if the bulb burned out it would be obvious as it wouldn't light up but it could be much easier to change a bulb with out much trouble. Just have the colored lamp cover screw off for lamp replacement. Of course due to the heat dependent resistance the current would start out heavier and then be cut back when the bulb filament heated up. ======================= Pat

 

[ridgerunnerinwv]

Just wondering if ridgerunner ever got his tractor started.

Well....?

I got my tractor started,it is starting part of the time and part of the time it is difficult to start. The thermistor is not completely bad,but is going bad. I ordered 2 new ones this past Friday and the dealer is going to send them to my house via US mail. I figured for $3.00 and a few cents apiece I would buy 2 and keep one for a spare.

 

[Soundguy]

That would be way to easy... they had to go find some arcane way that is difficult to fix.. so their shop techs can charge you 55$ an hour, vs you replacing a bulb in the dash for 3$.. etc.

Soundguy

Soundguy, I too was waiting with baited breath (no I didn't eat anchovies) to find out what the heck the thermistor was for. Oh well, does it simplify the ignitioin switch or what? In the olden days the start position of an automotive ignition switch gave full voltage to the ignition while cranking. Of course full voltage while cranking was probably well under 12 due to heavy draw. Then when you released the key switch it reverted to the "run" position and the current (and voltage) going to the coil was limited by the "ballast" resistor. If a ballast resistor went out the symptom was the car would start but when you turned lose of the key it would immediately die. I suppose the thermistor is in series with the coil exitation current going from the switch to the starter solenoid. Gee, they could have put a lamp socket on the dash and put a tungsten filament bulb in series with the solenoid coil. Tungsten exhibits a non linear temperature dependant resistance with low initial resistance that increases with temperature. This would have given the operator a light that came on when cranking and if the bulb burned out it would be obvious as it wouldn't light up but it could be much easier to change a bulb with out much trouble. Just have the colored lamp cover screw off for lamp replacement. Of course due to the heat dependent resistance the current would start out heavier and then be cut back when the bulb filament heated up. ======================= Pat

 

[ridgerunnerinwv]

I got the thermsitor and installed it. The tractor started fine last night,I will try it again today. The thermistor is not much bigger than the fingernail on my small finger.I bought 2 and am keeping one for a spare,they were a little over $3.00 apiece,but the shipping via UPS was over $8.00

 

[Soundguy]

You know.. now that you have a spare.. you won't need it. It's kind like insurance.

I twisted a front lugnut stud offa my Nh 7610s. I went and bought a bag of new studs and nuts. Having had the rim off another couple times... Of course.. no new breaks...

Soundguy

 

[ridgerunnerinwv]

You know.. now that you have a spare.. you won't need it. It's kind like insurance.


Soundguy

Ain't that the truth.........................

 

[JustaTreefarmer]

This past weekend after a year or so of intermittent "won't start" issue on my 4300 I found these threads on the problem and fix. First I found that a 1/4 inch drive ratchet and 10 mm shallow well socket gets behind the solenoid to the bolt closest to the engine block without removing anything. I still had to reach behind the solenoid to start the bolt to reinstall.

I have a couple of questions, is the problem that the solenoid allows oil to get behind the plunger and causes increased resistance that the circuit can't overcome or is it that the thermistor has slowly changed value over time and not allowing enough current on startup to engage the solenoid and open the fuel path?

Has anyone that replaced their solenoid or thermistor had the problem return?

I pulled my solenoid and cleaned the thick oil out of it and then the solenoid opened with the same audible level as when new. I am hesitant to replace the thermistor if the problem is really the seal in the solenoid?

 

[brtmotorsports]

I experienced the same issue with the fuel shut off solenoid on my 4700. After purchasing and installing an expensive new solenoid several years ago I realized the root cause of my problem after seeing all of the oil leaking out of the old one. That oil was hydraulically locking it up. As stated you can tell by the sound when you first turn the key. When it sounds muffled it's because there is oil in it. When empty it makes a loud, distinct click. It's been several years since I learned that lesson and my no longer "new" solenoid has occasionally started doing the same thing. I have found that if I don't hear the distinct click from the solenoid when I go to start my machine it requires that I simply turn the key on and leave it there for a few of minutes. It's a pain to have to wait but it always fires right up if I give it time. In my opinion it takes constant pull on the solenoid to force the excess oil from it and allow enough travel to let fuel to flow to the pump. Turning the key off and on again trying to start the tractor doesn't seem to discharge the oil. It's time to look at my old solenoid ( I'm a pack rat,couldn't throw a $165 part away) and determine what it takes to replace the seal. I never knew that a Thermistor existed so I've never replaced it. Not saying that isn't an issue but I'm convinced that oil leakage / hydraulic lock of the solenoid has always been the root cause when my machine fails to start. I may replace my thermistor and see if it reduces or eliminates the "leave the key on for a few minutes" solution I have been using recently. If it does then I won't care about oil leakage into my solenoid. Maybe the Thermistor was designed to provide the pull necessary to overcome the hydraulic locking of the solenoid all along.