JD 4600 won't start solenoid and termister replaced

Robert Rex · Jun 3, 2014

I'm new to this forum, read a ton of threads and posts on similar problems and don't find a direction. My JD 4600 just stopped, won't restart. It turns over just fine, at about the RPM I am used to hearing. I replaced the thermistor and checked the solenoid (before installing the new one I bought for $250!!). Out of the pump the solenoid works, pulls in while cranking. If I crank a long time it stays in so I assume the new thermistor is working. Old one probably did also but it's only a $6 part. The plunger in the injector pump (pushed by the solenoid to cut off fuel and stop the engine) seems OK. I can push it in with my finger and it moves back out smoothly when released. Checked the seat neutral switch, very frayed so replace connectors back to good wire, check continuity to make sure the circuit is made, it is. Recently did service so fuel filter is clean, cracked the fuel line at pump and determined that fuel is going to pump. I'm about to go back (it's dead in the vineyard) to loosen one of the injectors at the head to see if I am getting fuel there. I have no instruments to check the fuel pressure at injectors (which I believe is high, like 2000psi).

Question: can a new thermistor be bad? Can I check the ohms when cold - what resistance should it show?
If the solenoid is out of the pump and the solenoid is used to shut off the fuel shouldn't the engine start without it in place (I should have to push the arm inside the pump to cut the engine off). I read somewhere that this tractor could have a PTO neutral switch but I find none.

Is there a way to test the injector pump? A rebuild is like $750 and may not even be the problem. I've talked to the local dealer service manager twice. He said it could be the relay the helps run the solenoid but if that were the case I would think that the solenoid wouldn't wouldn't work. In fact when I removed the relay it didn't work. Am I missing something?

Any other ideas.
Thanks

Robert Rex · Jun 5, 2014

As it turned out the problem was not the thermistor or the solenoid or the injector pump. It was water in the diesel fuel. We use farm diesel, which is red. When I went to check the pump I noticed the "fuel" coming out was clear. The fuel tank had water in the bottom, not unusual with diesel. What I didn't remember to do is open the stop cock at the bottom of the fuel tank to empty out the water. It has risen far enough to be picked up by the fuel line. I bleed the lines at the injectors three times before I got all the water out and then it started and ran fine.

Now I have another problem. After running awhile it stopped and would not turn over again. Power to everything I checked but dead, like if it were not in neutral. I suspect a loose connection at the fuse block, which I pulled out to replace the thermistor. I pulled it out again but can't find any obviously loose connections wiggled them all. This now has me stumped. I still suspect this is where the problem is. Can't be the solenoid because it deals only with fuel cutoff. Has to be some loose wire, bad connection or at the outside, a bad relay. I'm having trouble finding a wiring diagram for this tractor, any help there will be appreciated or any insight on where to look next on the tractor.

4310 · Jun 5, 2014

You have the same luck that I do.

I can't offer much help but have you checked the battery? What I usually do is spend $300 on unnecessary parts and it turns out to be something simple.

patchnball · Jun 5, 2014

Hydrostatic????? push both forward and reverse pedals a couple times ( safety switch involved) ......make sure PTO is not engaged

Robert Rex · Jun 6, 2014

Battery tests strong. Transmission is shift, not hydrostatic. I'll try isolating the neutral switch on forward reverse lever. Can find wiring diagram anywhere. JD makes it hard to fix without such support. Thanks for the advice guys.

Tx Jim · Jun 7, 2014

parts schematics don't help much but terminal #27 states for trans & parts key 47 is NS switch. If engine turns over I think NS switch is OK. I think that the problem is associated with fuel control solenoid or it's electrical source.

mfreund · Jun 7, 2014

Did you load test the battery? I have had a few fail with 12v on meter but had no Amps when tested. One was a 10 month old battery in a Harley that was always on a battery tender!

Robert Rex · Jun 12, 2014

Turns out it was a bad diode and possibly one bad relay. I replaced the run relay and the V1 diode. I had no way to check either, other than check continuity between closed parts of the circuits. By swapping the K2 start and the K4 run relays with others that are less likely to be the problem, such as K7 Accessory Relay, I narrowed down the one that would create the problem, which was the intermittent failure of the stop solenoid. Turned out to be the run relay. I'm not certain how they are interconnected but you seem to need a complete set of K2, K3 and K4 relays for proper start and run operations. I had nothing to swap with the V1 diode and it costs about $15 so I replaced it. The relay costs about $20. A new stop solenoid cost $250!! I've attached a drawing of the relay layout, which I found on line after a long search. The JD dealer service manager was a help but mostly a a sounding board. Like most modern mechanics they tend to just install new pieces until the thing works, not knowing exactly how the circuitry is mapped. I think a diode or relay failure would be rare, but if you have replaced or determined that the solenoid and thermistor and battery and starter are good I would suspect the relays.

Thanks for your help and ideas guys.