Go Bottom870 Fuel shut off problem
 | Slate
Join Date: Posts: 1 
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2003-04-27 53874
I have a JD 870 and I am having an electricial problem with the fuel shutoff solonoid. It will not pull the plunger in and open the fuel. If I push the solonoid in by hand it will stay until the iginition switch is turned off.
I put a new solonoid on and it does the same thing. I tested the old one further and it will work if I hook directly to the battery. The solonoid must have two windings or magnets. One to pull the plunger in and another to hold it in.
Any suggestions where to look next?
Thanks,
Martin
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 | Peters
Join Date: Feb 2002 Posts: 3034 Northern AL 
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2003-04-27 53876
I would check the voltage across the solenoid in the normal position. If the voltage is low I would check the connections for corrosion and then see if there is another solenoid used to activate this one. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-04-28 53898
It sort of sounds like the switch under the seat problem discussed here several times but I don't know if that problem affects 870's.
A voltage check isn't bad, but relay circuits are often tested on the basis of current, although who know where specs could be found. A relay with a poor ground in operation might be weak but a voltage test to ground might read high rather than low. It would have low current and therefore low hold-in power. A poor connection on the hot side may result in low voltage and also low current and low hold-in power. I don't know if the fuel solenoid would have two windings like a starter solenoid or not.
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| jdgreen
Join Date: Jul 2003 Posts: 232 Maryland
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2003-04-28 53940
I believe the 870 has a time delay relay that operates the pull-in side of the shut-off solenoid. It should be mounted on the front top of the firewall just behind the engine. It sounds like this part is bad. ....
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| slate
Join Date: Posts: 1
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2003-04-28 53944
I have checked the voltage at the connection where the solenoid hooks into the wiring harness. There are three wires. One ground, two hot. When the iginition switch is in the on position one of the hot wire shows 12.46 volts and stays thatway until the switch is turned off. The other hot goes to 12 volts as soon as the ignition switch is turned on, but it goes to zero in about 2 seconds. The two second hot wire should pull the plunger on the solenoid in and the second hot wire holds it in. My information says that it takes 50 amps to pull the plunger in and about 1 to hold it. It must not be getting the entire 12 volts and 50 amps required to pull in the plunger. I also have another problem. The voltage going to the solenoid is intermittent. sometimes it's there and sometimes it's not. Yee Ha!
I'm trying to figure out how to test the relays you guys mentioned and the timer relay for the pull in side.
One good point - the tractor still starts and runs with the solenoid removed if you operatethe fuel lever manually. I'm afraid this negates all the safety switches or I'd rig up a manual kill switch out of a good stiff coathanger.
Thanks for the help. additional suggestions are appreciated.
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-04-29 53969
I did get my reasoning a bit messed up in yesterday's comment. I'll blame my now ancient teching experience. A component with a bad ground will measure full-voltage from the hot side to ground. A bad ground is just an extra resistance is series with the component and full voltage will be shown across a full series network. Likewise, a resistive hot-side connection will still measure 12V to ground because there's virtually no current flow through a volt meter.
If there are resistances in either the hot or ground side of the component, they won't affect voltage measurements. They will start dropping voltage when current flows though a component, which reduces current and the power of a solenoid. If current can't be directly measured when the solenoid is in operation, it might be solved from the total series resistance in the circuit and battery voltage.
If the ground wire is the only ground path in the circuit, a measurement from the plug to a good chassis ground, one across the solenoid winding and another from the hot wire to the battery terminal (disconnected of course) should give total resistance in the circuit. Battery voltage divided by resistance in ohms should give current in amps. I would note that many components receive their grounds through their cases and mounting bolts so the ground wire may not be the only ground.
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| Deere_Tech
Join Date: Jul 2003 Posts: 1 columbus indiana
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2003-04-29 53994
both windings must power up to pull solonoid to run position and then only hold winding be powered up when key switch in in run position.
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-04-30 54033
I'll some more guessing here. Deere Tech's comment made an important point. Both windings must work for the solenoid to pull in. A 50A circuit seems pretty heavy for operating something like a fuel shutoff and I wouldn't have thought that the hold-in winding would be needed as well.
That sort of complicates testing since both winding circuits have to be tested. I'm guessing the solenoid is designed like that so all safety interlock switches can be in the hold-in winding circuit. The fuel solenoid wouldn't energize unless all safety switches are closed. It sure starts sounding like a wiring diagram would be handy here.
It sounds like the hold-in circuit and related safety switches might be a good place to look. I'd keep in mind that safety interlocks are sometimes placed on the ground-side of the winding of a safety relay. In such a circuit, the hot lead wire and even the hot contact on another component such as the fuel shutoff solenoid always will measure full voltage. Such designs may not be all that safe since a short circuit around the switch would defeat the safety protection, but it's like that on my Ford.
If you're already jumping things and have a wiring diagram, jumping individual safety switches might help find the problem.
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| VaSlate
Join Date: Jul 2003 Posts: 1 Hillsville, Va
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2003-05-05 54350
Up Date - Thank all of you for your helpful comments.
I found a Mechanic that made me a copy of some of the test procedures for this problem. The diagram was great and illustrated where to test exactly. It started with the battery voltage and walked through point after point with expected results at each test point.
Even with this treasure of information, what you guys said helped me solve the problem. The voltage from the timer did read 12 volts for the 1.5 seconds it was supposed to without a load, butas one of you pointed out, sometimes the reading was different with a load. It was. It dropped to 0.5 volts with the solenoid hooked up. One of you mentioned that a poor ground would cause a lack of power in a load, so I wired in a direct ground and the solenoid would work once in a while, but got very hot. I got voltage and continunity across the 3 amp fuse to the delay timer but when I took off the fuse panel to check points behind it, I noticed that the Time delay switch kept clicking on and off. I isolated one of the fuses causing the clicking when I touched it. It wasn't the fuse but a loose fitting fuse. It was held tight enough to test ok but too loose to carry the 12 volts under load. I bent the contacts together where the blade fits into and it works great now!! Exceptwhen you engage the PTO with the transmission in gear, Then it cuts off. It will reopen the fuel if you take it out of gear. I've got a bad seat switch also. One of you mentioned that possibility also. The solenoid quit working about a year ago and then quit holding itself in at all lately, I guess when the seat switch went bad.
I've got a new one coming. Right now I've got it jumped so it works all the time, but no safety switches.
Thanks again to all of you for you interest and help. If you have a similar problem or electrical problem on a similar tractor, let me know. I'll tell you a few places to check.
Yee Hah!!
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2003-05-06 54378
Sounds like a pretty good outcome. The fuse holder solution was the same one that I found for an intermittent lighting problem I had. I finally it out when I noticed that the holder contacts had voltage on one side of the fuse but not the other. I figured it was a bad fuse and put a new one in which didn't cure the problem. I finally check for continuity across the fuse, which indicated the fuses were good. The holder contacts were about the only explanation left.
I'm guessing that the ground path for the solenoid that got hot has another component in it before the circuit gets to chassis ground. Another component would provide more resistance and reduce the current flow. That's also the explanation if it's the same point where voltage dropped under load. Several loads in series divide the total up voltage across them when current is flowing but not when it isn't. Trouble-shooting nightmares can happen when several things wired in series have a broken ground at the chassis connection. Every point tested in the circuit will read battery voltage. A common conclusion and one that I've made is 'Yep, that's got voltage, it must be working.'
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