John Deere 4400 hard to start/thermistor maybe?

[ridgerunnerinwv]

My JD 4400 is very hard to start at times,a few years ago while under warranty the dealer replaced the ( spelling ? ) thermistor and it solved the hard starting problem. My question is,where on the tractor exactly is the thermistor located at ?? What would the part number be ??? I think it may need replaced again and I want to fix it myself.

Thanks

 

[Soundguy]

A thermistor is an electrical component that has a resistance that changes with temperature. (This is a real basic explanation)

I can think of quite a few applications in an electrical system that 'might' use a thermistor.. like a fan sensor.. or a heat sensor in the hyds / tranny.. etc. I'm not too sure where one might be used in the ignition system..? (sensing for precomb chamber heat from a thermal start assist?????? )

Is there any chance he refered to a 'thermostart system' or glow plug instead?

Soundguy

 

[ridgerunnerinwv]

A thermistor is an electrical component that has a resistance that changes with temperature. (This is a real basic explanation)

I can think of quite a few applications in an electrical system that 'might' use a thermistor.. like a fan sensor.. or a heat sensor in the hyds / tranny.. etc. I'm not too sure where one might be used in the ignition system..? (sensing for precomb chamber heat from a thermal start assist?????? )

Is there any chance he refered to a 'thermostart system' or glow plug instead?

Soundguy

Soundguy,
Thanks for the quick reply !!! I just done a search and there are others in the past that had trouble with the thermistors http://www.tractorbynet.com/forums/search.php?searchid=145485

I am not sure where to go and look exactly...I will call my dealership if know one here tells me where to look.

Thanks for your " basic explanation" of how a thermistor works.

 

[Soundguy]

Nothing came up on that search.. what did you find?

Soundguy

 

[ridgerunnerinwv]

Nothing came up on that search.. what did you find?

Soundguy

I do not know what happened to my link ...I just typed in thermistor on the search feature and I found a few posts of others with themistor problems on John Deeres..

 

[dbdartman]

Oooooo...! A question I can answer!

The thermister is located on the back of the fuse panel. It's a tiny little thing that costs about $3 & takes about 2 minutes to change (after you take about 2 hours getting to it ) Once you unbolt the fuse panel, you should have just enough room & slack to turn it so you can see the thermister (it's about half the size of a dime with 2 wires, tucked in with the wires).

I had an occasional "no-start" condition on my 4400 late last year that turned into a constant no-start, so I started changing things in the spring: First was the fuel pump start solenoid ($$$$!), then battery cables (old ones were getting crabby), then I went through the ignition switch & solenoid electrical functions (the service manual is severely lacking in this particular case) & finally arrived at the thermister. Once that was changed, it has started immediately every time it is called on. I didn't even have to start it to know it was fixed, though. With the new solenoid on the pump, just turning the ignition on resulted in a pronounced "KLACK" of the solenoid being retracted.

Trouble-shoot like this: Unbolt the bracket behind the solenoid on the rear of the fuel pump (fuel line passes through it, gives room for ratchet & extension) & let it hang. Remove the solenoid from the back of the HP pump (be aware it will likely have some oil in it) & turn the ignition switch on. The soleniod pin should retract. If it doesn't retract, it's pointing toward the thermister being bad. Now, try to start the engine. If it fires right up, it's probably the thermister causing the hard start (although it could be the solenoid). If it doesn't start immediately, your problem is elsewhere. To stop engine (if/when it starts with solenoid removed) just push the lever in the HP fuel pump where the solenoid was with you finger until engine stops completely (this shuts the fuel off).

 

[ridgerunnerinwv]

Oooooo...! A question I can answer!

The thermister is located on the back of the fuse panel. It's a tiny little thing that costs about $3 & takes about 2 minutes to change (after you take about 2 hours getting to it ) Once you unbolt the fuse panel, you should have just enough room & slack to turn it so you can see the thermister (it's about half the size of a dime with 2 wires, tucked in with the wires).

I had an occasional "no-start" condition on my 4400 late last year that turned into a constant no-start, so I started changing things in the spring: First was the fuel pump start solenoid ($$$$!), then battery cables (old ones were getting crabby), then I went through the ignition switch & solenoid electrical functions (the service manual is severely lacking in this particular case) & finally arrived at the thermister. Once that was changed, it has started immediately every time it is called on. I didn't even have to start it to know it was fixed, though. With the new solenoid on the pump, just turning the ignition on resulted in a pronounced "KLACK" of the solenoid being retracted.

Trouble-shoot like this: Unbolt the bracket behind the solenoid on the rear of the fuel pump (fuel line passes through it, gives room for ratchet & extension) & let it hang. Remove the solenoid from the back of the HP pump (be aware it will likely have some oil in it) & turn the ignition switch on. The soleniod pin should retract. If it doesn't retract, it's pointing toward the thermister being bad. Now, try to start the engine. If it fires right up, it's probably the thermister causing the hard start (although it could be the solenoid). If it doesn't start immediately, your problem is elsewhere. To stop engine (if/when it starts with solenoid removed) just push the lever in the HP fuel pump where the solenoid was with you finger until engine stops completely (this shuts the fuel off).

Ahhh....Now we are talking...I appreciate very much your time to type your reply and share with me what you have told me.

 

[Soundguy]

Ok.. I'll bite.. What are they using the thermistor for in the circuit? I.E. is it heatsunk to any particular component in the fuse box.. ? a breaker or something? A shunt?

Soundguy

Oooooo...! A question I can answer!

The thermister is located on the back of the fuse panel. It's a tiny little thing that costs about $3 & takes about 2 minutes to change (after you take about 2 hours getting to it ) Once you unbolt the fuse panel, you should have just enough room & slack to turn it so you can see the thermister (it's about half the size of a dime with 2 wires, tucked in with the wires).

.

 

[dbdartman]

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.

 

[Soundguy]

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.

.

Hmm.. well.. there are better ways to have limited the current in the solenoid circuit, from initial pull in, to hold.. however.. if it works good with few problems.. I guess it may be cheaper.. etc. that's what the bean counters like..

Soundguy