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Curtis B.
Curtis B., Technician
Category: Small Engine
Satisfied Customers: 12726
Experience:  have worked on and around most engine models for 35 yrs./Polaris ATV expert
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John Deere D105. Was running at lowest idle 30 sec.

Customer Question

John Deere D105. Was running at lowest idle for about 30 sec. PTO off, and in neutral. Then started to slow down, like it was going to cut off. I was about 20 feet away and couldn't move the throttle. Suddenly cut off with one loud backfire, like a single gunshot. Had just finished mowing about 20-30 minutes worth. Engine seemed very hot to what I remembered. Engine has 2.2 hours on it.
Now - won't turn over, starter is not even attempting to move.
Thoughts?
Submitted: 1 year ago.
Category: Small Engine
Expert:  Curtis B. replied 1 year ago.
Welcome to JUST ANSWER small engines, let me try to help you !! Can you turn the engine manually by moving the upper screen above the flywheel? Is engine full of oil? Could oil be thinned by gas in the oil? Does starter engage flywheel, but does not turn engine? Engine may be seized! Is this a new mower. or new to you? If oil is ok, and engine is seized, do you have any warranty left on the unit?
Customer: replied 1 year ago.
Had not tried to turn the screen above the flywheel. Just tried that. It turns both ways through several full rotations. In one direction, there is not much compression. In the other direction, it must be giving full compression, because it is difficult to turn all the way around, but it can be done. It seems normal compared to other engines of that size, ie, no scraping sounds, rotates smoothly, good compression, so it is not seized, thankfully.The tractor is brand new to me, 2.2 hours on engine timer, drove it home from the Lowes around the corner.The engine has the correct level of oil as shown on the dipstick. It seems a little thin. I think it smells faintly like gas, but my wife does not think it smells like gas. So we're not certain whether there is gas in the oil.After rotating the screen/flywheel a few times through several compression cycles, there seems to be a little pressure in the dipstick tube. When I turn the lid and remove the dipstick, there is the sound of air escaping (or being drawn in, can't tell). So there is either some air pressure in the oil chamber, or a slight vacuum.The starter does not seem to work at all. When I turn the key, the headlamps come on, and the 20 amp automotive fuse is intact (not blown). But when I turn the key to the start position, the headlamps go out, and there is no sound. A car will usually make some sound like is trying to turn the starter but can't like if the battery is dead. The tractor doesn't do anything- no sound, no click, nothing.It seems to me like it is electrical somehow - the starter never makes any sound, never engages, no rotation anywhere at all. But how could a hard backfire break the electrical/starting system?What next?
Expert:  Curtis B. replied 1 year ago.
I question the battery and the battery cables! Do you have a voltmeter to test the battery? Have you checked the cable connections? The engine may have backfired when the fuel solenoid closed from lack of battery voltage. With lights dimming, it seems battery voltage is low.
Customer: replied 1 year ago.
The battery is a 12 V battery according to the label.The voltmeter reads 12.45 volts with the key off, and 12.11 volts with the key in the headlamp position. When I turn the key to the run position, the voltage comes back up to 12.45 volts. I think there may be a switch that turns off the headlamps in the run position until the engine is running?Then, when I turn the key to the Start position, the voltage does not change at all, not even by .01 volt - it stays exactly on 12.45 volts.So it seems like there is something keeping the starter motor from getting any power. There's no sound, no click, no rotation, nothing, and the voltage does not drop by even a tiny amount.I checked the only fuse I can see and it's good.Could there be some kind of protection circuit, or interlock, or something to explain why there seems to be no power going to the starter? Could that protection have been set by the sudden backfire?I'm stumped.What next?
Expert:  Curtis B. replied 1 year ago.
If you follow the battery cable to the starter solenoid, can you jump the solenoid from the battery post to the single switch terminal and spin the engine? This is test of battery, cables and starter solenoid and starter. If it spins, you are correct that it is likely a safe switch or interlock. Have you checked the seat switch and harness?
Customer: replied 1 year ago.
There is no harness, but there is a seat switch. I was sitting in the seat when trying to restart the tractor, but the starter would never engage.I did as you suggested and traced the battery to the starter solenoid. In the D105 they are right next to each other. The starter is also on that side of the engine so everything is clearly visible.I used a standard car jumper cable to connect the positive battery terminal to the red output cable from the starter solenoid, the cable running from the solenoid to the starter motor. I could have just touched the jumper cable to the starter motor as well. I did not use the black side of the jumper cable at all. This bypassed the starter switch as you said. The starter motor immediately turned, as did the flywheel and screen.I tried the starter switch again, no luck.The engine sounded like it had compression, so I set the choke on and touched the starter motor again. I also set the parking brake and made sure the tractor was not in gear, and that the transmission lock (which lets you roll the tractor when it isn't running) was engaged, so the tractor would move if it were in gear and running (ie normal position).The tractor started up almost right away!I jumped on the seat. After a few moments of relatively heavy blue smoke (guessing there is oil in the exhaust?) I pulled the choke off, which sets the throttle to maximum. The exhaust cleared up as usual and the motor was running fine.I pulled the throttle back to about 1/2 to 1/3 and let the tractor idle for about 20 seconds. Then I put the tractor gear and drove it about 20 yards to put it under my back deck, where I am keeping it until I make more room in the shed. When it cools off I will put the cover on.Tractor ran fine. When parking it, I ran the throttle up to full for a few seconds, then back down to 1/3 for a bit before switching off the motor. The motor switched off fine.The exhaust smelled a little funny when I switched off the motor, like it had gas in it, which didn't make any sense. Also had a faint oil smell, but that didn't seem unusual.After 10 minutes I tried to restart the tractor: parking break set, out of gear, transmission lock set engaged, PTO off, sitting in the seat. No joy. Exact same result: it will not start with the key.I didn't try to restart the tractor by jumping the solenoid, but I'm sure it will work fine.So, great advice, I was able to get the tractor running enough to get it put away.So I'm guessing the problem is:
1. Starter switch bad
2. Solenoid bad
3. Interlock I can't find to resetBecause the tractor is brand new, I'm having trouble believing something is broken.Also, I'm concerned about the seemingly high temperature when the tractor backfired.I will study the manual more to see if there is something missing interlock-wise, but I'm still stumped.Now that tractor is out away safe, what do you recommend I do next?
Expert:  Curtis B. replied 1 year ago.
Seat switch, brake switch, pto switch. That should be all the safetys! Has to be a safety switch as the fuse is good, and he battery is good enough to start the tractor when you jump the solenoid! I assume you had the blades off!