John Deere 770 790 Just quit..

[Industrial Toys]

Thought I would post this to add to the 770/790 database.

Neighbour showed up pulling the JD770 (circa 2000) that I sold him years back. Still in really nice shape. Says it was running and just quit. Would not restart. TRACTOR HAD SAT UNUSED IN AN UNHEATED CONTAINER ALL WINTER.

Right off the bat, I noticed that the fuel solenoid wasn't clanking on.

Noticed that a dealer must have changed the seat switch to something electronic like a prox sensor. There used to be a plunger, that you could pull up for unattended PTO operation.

Found a blown 5 amp blade fuse on the left side, second up from the bottom. Replaced and solenoid still did not operate.

Found 12 volts going to the two wires of the fuel solenoid. Possibly hold and pull. I don't know how this works. So Suspected the solenoid at this time.

BUT, it didn't quite make sense, so I connected a 12 volt gell cell to the solenoid with the black wire as negative. Solenoid works.

RECONNECTED and tractor started right up. Returned to neighbour. What the heck?

 

[Richard001]

Loose or bad connector, removing and reconnecting often helps.

 

[Industrial Toys]

Thanks. I think, that was the first thing I did. Nada. Maybe if I knew how the pull/hold system worked. Is there a contact in there?

 

[Richard001]

Thanks. I think, that was the first thing I did. Nada. Maybe if I knew how the pull/hold system worked. Is there a contact in there?

The Yanmar 3-cyl diesel engine uses a fuel solenoid that has two coils. A pull-in and a hold coil, or at least the ones that we used at the over-the-road refrigerated transportation company I worked for.

The pull-in coil should only be energized for a second or two, otherwise the coil will overheat and destroy itself, it is a rather high current coil. The hold coil is used as it's name implies,it holds the solenoid open during the time the engine is running.

If either coil is not energized in the proper sequence, the fuel solenoid will not operate.

Richard

 

[Industrial Toys]

So, I am curious, what switches the pull and hold coils. They could have put a single set of wires going in with an internal contact to switch out the pull coil when it is activated.

Seems like he lost his hold coil and then didn't have his pull coil either for a restart. Maybe the common ground?

Still curious what the 5 amp fuse was for.

 

[Richard001]

This is what it looks like and this one has two wires, but it must use the body for the ground connecton.

Robot Check

I should have added that there is a controller that turns on both coils and then automatically turns off the pull-in coil.

Sorry don't know what the 5A fuse does.

 

[Industrial Toys]

Anyone know about that apparent upgrade of the seat switch?

 

[beenthere]

There is a part # M803327 for a seat switch.. Look at that and see if that is the one you refer to here.

 

[Industrial Toys]

That switch as the plunger. Maybe I should look at it closer next time. Possibly someone just capped it off, disabling it. Looked like some prox sensor to me.

 

[Industrial Toys]

Update. Neighbor drove up yesterday with the 770 and a case of TUBORG.:drink: Says fuel solenoid had quit again and the fuse I replaced had blown again. Bought solenoid at dealer for four hundred something, CDN. All is fine, for now.

My guess, is that the HOLD coild was going bad, windings shorting out.

Says he used a stick to keep solenoid open until repairs could be effected. Proud of him for that insight.