F935 cranks but won't start, has run perfect

pclose · Jun 29, 2020

I've had a F935 for 3 years. I like the machine. It's always started and run fine. I've cut grass with it a few times a week since March, no trouble. Last week I started the machine (started right up) drove it no more than 100 yards, realized I'd forgotten to do something inside. Drove it back into the garage and turned it off. 10 minutes later it wouldn't start? It wont start. It cranks fine. Battery is a little old so I swapped batteries with a new one form my tractor. I checked fuel delivery and it's good. Oil was good. Fuel solenoid snaps shut good. Glow plugs is about the only thing I havent checked. Could that do it? One weird thing is that I was getting white smoke puffing from the muffler the first time I tried to start it, now I dont get much. There is much more coming from the blowby tube than the muffler and that was not happening before...of course it has always started right up so I didnt pay close attention to what it did before. The only thing I did to it between it running and not, was tighten the PTO drive shaft belts. I cant imagine that having anything to do with it not starting,. Any ideas? It doesn't consume much oil. It doesn't make smoke. It's always started...until it didnt. Your help is greatly appreciated!

grsthegreat · Jun 29, 2020

doesnt that mower have a couple of safety switches...like a seat switch and a brake switch? have you checked these

beenthere · Jun 29, 2020

grsthegreat said:
doesnt that mower have a couple of safety switches...like a seat switch and a brake switch? have you checked these

Wouldn't allow it to crank if they were involved, would it?

Diesel, right?

:welcome to TBN

https://www.tractorbynet.com/forums/john-deere-lawn-garden/280116-john-deere-f935-wont-crank.html

Kyle_in_Tex · Jun 29, 2020

beenthere said:
Wouldn't allow it to crank if they were involved, would it?

Diesel, right?

:welcome to TBN

https://www.tractorbynet.com/forums/john-deere-lawn-garden/280116-john-deere-f935-wont-crank.html

Ahhh, the old fuel tank internal tubes.

Welcome to TBN pclose. Please let us know what ends up fixing your machine.

pclose · Jun 29, 2020

thanks for replying. Yes it's diesel (yanmar) and I've been there and done that with fuel lines. It's also filled to the caps in both tanks with fresh fuel to rule out a line problem. Yes, it has a bunch of safety switches and mine are all still functioning. It wont crank at all if its a switch. It cranks fine but makes no effort to start. I'm pretty sure I ruled fuel issues out but I will dig into it further and make sure my replacement tank tubes are still good. I replaced the pump when I did that 3 years ago. I can hear it work and it sprays fuel when i open up the bleeder. It's an oldy, but I would rather rule out common stuff before looking at engine internals. The blowby is a concern, but it was running and I turned it off. In my experience, when it's an internal problem, they've turned themselves off. Last time, the really upset engine part quit work and broke out of the engine (Shibaura). I didn't need this forum to diagnose that one... but I should have shared the pictures!

TractorGuy · Jun 29, 2020

I would double check the fuel shut off solenoid. It should pull all the way open when starting. Might have someone pull on the rod while it's being cranked. Crack an injector line and make sure fuel is feeding while cranking also.

pclose · Jun 30, 2020

Thanks for the input! I did as you said and the solenoid pulls tight with no play and I could not pull it back while cranking. Cracked all three injectors and they all get fuel. Still nothing. Do you think too much fuel has gone into the cylinders? Is that even a possibility? Lots of cranking has gone on.

pclose · Jun 30, 2020

I've been thinking about what I did between the mower running, and not mowing. I didnt originally admit this, but it's time for full disclosure. I've recently replaced the belts and bearings on the PTO clutch and drive side, when I engaged the mower it sounded wrong so i stopped it and discovered that the bolt and washer at the end of the PTO driveshaft had come loose and the belt drive pulley was able to slide. I only mention this (aside from the relief of coming clean and facing my shame and guilt lol!) is that on in order to hold the top of a bolt that needed to be tightened and loosened, I removed a bracket that holds the glow plug relay. Deere is $70 proud of this little gizmo, but it was definitely involved in what happened between running and not running. Do these go bad? How would I know? My glow light comes on and goes off normally when i turn the key. I'll clean up the contacts on it real good and make sure it's seated correctly and try starting again. I didnt know what that relay did, but now that i do...i'm hopeful it could be the problem

TractorGuy · Jun 30, 2020

If you have unrestricted air intake, fuel and compression it should start.

Compression Pressure
3TN75, 3TN78, 3TN82,
3TNA82, 3TN84
(870 CUT, 955 CUT) . . . . . 2448 kPa (355 psi)
3TNC78 (3011 OEM),
3TN84 (3014 OEM). . . . . . 2158 kPa (313 psi)
Maximum Difference Between
Cylinders . . . . . . . . . . . . . . . . . . . 490 kPa (71 psi)

TractorGuy · Jun 30, 2020

I guess you have verified it is fuel at the injectors and not water?

I wouldn't ordinarily suggest this but you might try a little squirt of starter fluid. Emphasis on little.