MF50 Diesel Starting Issue

Bill VA

Well-known Member
Need to do a little more work with my volt meter, but my MF50 diesel would not start after what I thought was a welded starter solenoid from a low voltage try at starting. That was somewhat conformed when I put a jumper on the battery and the starter immediately engaged - solenoid wasn't disengaging. Pulled the starter and replaced the solenoid, put everything back, no start.

When I turn the key to start, the amp meter shows a strong negative response, like there is a short, but no click from the solenoid. I assume the neutral start switch is OK, else there would be no movement of the amp meter. I ohmed out the start switch earlier and it's good.

What do you think is wrong?

I need this tractor ASAP for some haying. I'm thinking for a band-aid of jumping the switch with a push button and fuse to the 'S' start terminal on the solenoid to see if I can get the tractor going. Sound like a good/bad idea?

BTW, the solenoid, old and new had a second terminal labeled 'R'. What is the purpose of this terminal?

Any sage advice is much appreciated.

Thanks!
Bill
 
Might re-check all your cable connections, could be a bad ground too. Cables can sometimes go bad inside with green stuff growing. You don't need the R terminal on diesel engines, it's for gas engines to by-pass the ignition resistor to place full voltage to the coil during engine cranking only.
 
When you replaced the solenoid did you swap the plunger too or just put the new body on the old plunger? Sometimes they are different enough in size to not work properly.
 
Good advice from Dieseltech, I just had a time with my 205 industrial and found bad battery cables. The problem was the replacement terminal ends that clamp onto the cable with 2 1/4 inch bolts. They had loosened up. Made up some new cables with soldered clamps and lugs. She spins like a top now.
 
Looking at the wiring diagram and from what I recall when I ohmed out the switch, there are 3 poles on the switch. Constant power from the battery/generator via a conmection to voltage regulator, momentary start pole that runs through the neutral safety switch to the start side of the solenoid and a counter clockwise actuated pole to the thermo start heater. It all looks ultra simple, including how the gauges are powered, not from the switch, nut the generator. I assume if the generator or is not working, the gauges won't work - a sign you've got generator issues?

So when I replaced the solenoid, nothing was bound-up that I could tell - nothing welded.

Question is - previously when I put a jump starter on the otherwise dead battery, why would the engine have wanted to crank? The switch seems to ohm out. Maybe I need to give it another look.

Also, wonder why MF used a copper buss bar to the lights vs a heavy gauge wire? It makes for a tight fit when trying to troubleshoot the switch.

Thanks,
Bill
 
One more thought for a band-aid and trouble shooting route. Looking at the wiring diagram, it looks like I could come-off the 'L' terminal to the neutral start switch with a momentary push button switch and bypass the start switch all together. If that works, I've isolated the key switch without cutting any wires.

Much to do this morning.....

Thanks!
Bill
 
Most starters have a nut underneath the cable connection that should be held to prevent the inside from shorting out when making connection.
 
Update - no luck.

Bypassed the key starter switch with a momentary push button switch. From leg 'L' off the voltage regulator to the 'S' terminal on the solenoid. Keep in mind the solenoid is new and starter is almost new.

Push the switch (range and gears in neutral and the fuel shutoff - off), the starter spins like a champ - yippie!!!!!

Let off the switch, the starter keeps turning - dang. Luckily the hot side of the battery wasn't cranked down and I quickly pulled off the cable to the starter.

Put the battery cable back on, no cranking (as it should be), pushed the momentary switch, starter spins great, won't stop spinning - again quickly pulled the battery cable to the starter.

Almost new starter, new solenoid. What the heck is going?

Again what got this going was a low battery and the thought that I had welded the solenoid via low voltage. Changed out the solenoid, turned the key and nothing. Today's effort was to bypass the switch and be sure the solenoid/starter would work, isolating the switch, but what I've got is a continuous running starter motor after initiating a start via the switch.

What do you think is wrong?

Also posting to the main board for a wider audience.

Thanks!
Bill
a170229.jpg
 
X2.. Lesson i learned a long time ago is just because something is a new part does not mean it's a good part.
 

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