755 hard to start, won't idle

[nightskyisme]

My 755 which has always started no problem, all the sudden won't start....when I crank it at high throttle and hold in that gold solonoid next to the feul injector unit, It runs fine @ high idle, as soon as I release the plunger, it dies.....it never really idled very well, shook and shuddered unless I increased the idle.
Fuel is ok, bled the lines and all seems ok....only puffs smoke and doesn't start now.....any ideas? Thanks!

 

[JD755]

That solenoid is the fuel shutoff. It has two electrical coils in it. The first one has power while the key is ON, the second only has power while the key is turned to START. The first one only has enough power to keep the solenoid engaged. It does not have power to pull in the solenoid from an OFF condition. The second coil, on during START, is what will pull in the solenoid. The first coil will then keep the solenoid engaged after the tractor is started. When the key is turned OFF, it will disengage and shut off the fuel. This system prevents fuel flow to the cylinders each start sequence until the key is turned past ON, to START. Sounds like the hold coil is not working. Watch the operation of the solenoid during start and run. It should stay engaged until the key is turned back to OFF. BTW, my 755 has never idled smoothly at low rpm. I just let it idle slightly faster than minimum.

 

[nightskyisme]

Thanks for that info, I see a white wire going to the starter and the double-connector as well. I think is does retract while cranking, but not when running....but would that keep it from starting? I think something else is wrong....and when I mean it doesn't idle smooth at idle, I mean it rocks the engine so much it tore 2 of the motor mounts, which is why I bought it so cheap....I just ignore it because I only use to to cut the lawn (at high idle).........

 

[JD755]

You are correct that the white wire from the starter is the connection to activate that second coil. Sounds like that part is working OK. The red wire on the solenoid connector provides voltage to the first coil when the key is ON. That red wire runs to a connector just above the coil. If you have a voltmeter you should be able to check for 12 volts on the back side on the connector where the pink and yellow wires go in to make the connection to the red wire on the other side. If that is OK then the coil is bad. If the voltage is not OK, then you not only have no power to the coil, but you also have no power to the thermo-start controller that activates the glow plugs and the preheat dash light. Does that light work OK? If not it would be a first indication of no voltage to the coil.

When the first coil is not working, it will immediately shut down the engine when the key is returned from start to run. Does the engine act like it is starting and so you return the key to the run position? In your first post you said it would run if you held in the solenoid. Is that still the case? If so, then the problem is definitely the coil. Sorry to hear about your severe vibration. I have no answer for that.

 

[nightskyisme]

Thanks for all your time on this: Yes, the glow-plug light does come on ok, but yes, your right, it was running great as long as I held the key to the start position.....then when I got it running enough, I would zip-tie the solonoid (coil) in the closed position and run the tractor at high idle. I will check the voltage when I get home tomorrow and see what I have....that coil is like brand new, it was replaced a year ago (by the previous owner) and only has like 20 hours on it....is it a known failure item? I bet it's not cheap.

 

[JD755]

I am not aware of that being a problem part, but I would not expect it to be. Mine has never failed in 16 years. JD Parts shows a new one is $120! Since yours was replaced not long ago, I would spend some time checking the connectors for dirty contacts or corroded wires. If you feel comfortable doing so, you could test the solenoid by unplugging the connector and applying 12 volts directly to the red (+) and black (-) wire contacts. The solenoid should then stay retracted after you simulate the white wire connection by just manually closing the solenoid and letting go.

You could also test for excessive return spring force on the solenoid. Disconnect the plunger pin so there is nothing for the solenoid to work against. It just involves removing a cotter pin. Then turn the key to run position and push the plunger in. Now see if it exerts a pull against you trying to pull it back out while the key remains in the run position. I should probably clarify this first coil cannot actually pull in the plunger. It is really an electrically activated latch that can hold the plunger engaged after the second one from the starter wire pulls it in. It is that latch you would be pulling against.

 

[nightskyisme]

Thanks, Ill try that and let you know...but would this solenoid "malfunction" actually cause the engine to not start at all (unless I play with the throttle and spay a little ether)?

 

[JD755]

Probably the best way to say it is, with a bad solenoid as soon as you take the key off START position the engine will not run. Does the engine crank and crank with nothing that seems to catch? Or is there a sense of starting and so you let off the START? You could of course have an additional issue with fuel, but I would solve the solenoid issue first and go from there.

 

[kennyd]

Thanks, Ill try that and let you know...but would this solenoid "malfunction" actually cause the engine to not start at all (unless I play with the throttle and spay a little ether)?

Be VERY careful with ether and glow plugs, BAD and EXPENSIVE things can happen to your engine!

 

[JD755]

kennyd is right. I forgot to mention to stay away from the use of ether.