4110/15/et al fuel shutoff solenoid readings/bypass

al3 · Sep 7, 2015

Has anyone confirmed the JD manual test values of 12.4 and .4 ohm on a new fuel shutoff solenoid? My history with failing windings is that the ohm reading usually go down as the windings short. Mine are almost double that on a machine that is having starting issues. It always cranks, but doesn't always start

All started when my 10 year old Optima (RIP) finally died on a nice 90 degree day. Tractor stopped in its tracks, battery voltage was just about zero; I figured as the voltage went to zero the fuel shutoff solenoid wouldn't stay open and it just died. However, when then replacement battery was installed, the 4110 wouldn't always start. Cycling the key all the way to the off position and then start a second time would usually result in a start. This didn't happen all the time, i.e. it often started normally on the first attempt.
Did all the relay voltage tests outlined in the shop manual (starter and fuel pump relay, glow plug relay) and all checked out fine. Wound up replacing both the glow plug and fuel pump relays as long as I had the counsel apart. Problem still pops up. (No fuel restrictions, cleaned lines, new filter)
The fuel shutoff solenoid currently on the tractor has two high ohm reading---manual calls out 12.4 ohm for two of the tests and .4 ohms for one other. I measure 28 ohms for each of the two and about .25-.3 ohms for the other.

Also, has anyone damaged their ECM running in a low battery condition? Looking at the wiring schematic is depressing---sure are a lot of ways a bad/damaged ECM could screw up the correct signal to the fuel solenoid. Would be great to just send voltage to the solenoid via separate switches and bypass all the ECM no-run/no start conditions. A�nyone done this?

JD755 · Sep 8, 2015

The high current pull-in solenoid coil on my 755 simply connects to the starter motor. The low current hold-in coil is connected to have power until the key is moved to the OFF position. This is how JD did it before all the electronics. Never had a problem in 22 years.

al3 · Sep 10, 2015

JD755. Yea, that's what I have in mind. Pretty easy to find a source of battery voltage, not too sure where to source the low voltage if I'm trying to bypass the ECM. Couldn't find the low voltage spec in the shop manual.

New switch arrived; ohm readings are same as the old one; info in the Deere shop manual is incorrect.

And to further screw up the day, discovered when a block heater is installed, there is no access to the one of the bolts attaching the solenoid to the fuel block assembly. Will have to pull the block heater (and coolant) to simply change out solenoid. Picture attached.

BTW, if you're looking at this and considering changing out your glow plug relay, you'll have to lift the gas tank in order to get to one of those attaching bolts.

So, do yourself a favor and don't let your battery discharge to zero. From the other posts reviewed doing so looks like a good way to start spurious electrical issues

JD755 · Sep 11, 2015

The typical solenoid does not need a low voltage. One coil, the hold-in, just draws a low current from the 12 volts. It does not need much current since it only holds a latching link in position. The other coil, the pull-in, needs a lot of current to pull the rod into position for latching by the holding link. The 12 volts should only be on the pull-in coil for a brief time, while the engine is starting. If it had continuous 12 volts it would burn up from the heat. Using either a starter motor connection or the automatic operation of the ECM will accomplish this. 12 volts is applied continuously to the low current hold-in coil until the key is turned off, at which point the holding link will move out of the way and the solenoid will move back thus shutting off fuel flow to the engine.

Watch the solenoid while you start it. If it fully pulls in while cranking, the pull-in coil is fine. If it does not stay pulled in after cranking then the hold-in coil or associated wiring has a problem. Measure for 12 volts at the hold-in coil. If that is good then there is a problem with the coil, such as your resistance measurement would indicate.

al3 · Sep 12, 2015

Thanks for the thoughts JD755.
Went through the shop manual again, found a spec for the fuel solenoid. Says the pull in voltage is 6.8VDC and the hold voltage is 3.0 VDC. Assuming the spec is accurate, looks like I just can’t run 12V line voltage directly to this solenoid without it overheating.
Did some looking around, there are clearly some chips (IC voltage regulators) designed to do this which is probably what’s buried in the ECM.
Also saw some products designed to lower 12V for specific products, most common is to 5V to power USB stuff. I know this is also an issue that has to be addressed when switching running lights to LEDs. So I’ll continue to look for an off the shelf solution before building a circuit board.
Anyone got thoughts on how to figure out the amperage draw of a typical 12v solenoid coil?

JD755 · Sep 17, 2015

6.8 is simply the minimum voltage required to pull in the coil. Anything below that is not guaranteed to pull it in. 12v should be applied. 3.0 is the voltage at which the coil will drop out when shut off. These are typical hysteresis values for a solenoid designed to operate on 12 volts. They insure the coil has sufficient margin to operate in real world conditions. 12 volts may not always be solid, but will be above 6.8. Due to peculiarities in the circuit, the voltage may not go to zero when off, but will always be below 3.0 volts. Due to the magnetic field generated when the coil is energized, the voltage to turn it off is less than the voltage required to turn it on. That is the hysteresis range.