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.

 

[nightskyisme]

Yeah, I am aware of the volatile natue of the ether....I just put a "wiff" of it near the intake and waited a good minute just to see if it started.....Ill hold off on it for now....thanks

 

[nightskyisme]

Well, applied B+ to red and ground to solenoid leads.....doesn't pull in, but when I pull it in, it locks and stays in until I remove the voltage.....when I turn the key to start it (still wont start) the solenoid pulls right in while cranking, so I assume this is operating as it should? Guess I should start checking fuel-related items now?

 

[JD755]

Sounds like the solenoid is working correctly. That's good. But since you have to manually hold it in while the engine runs you need to insure 12 volts is applied to the red wire during use. There is still the possibility of dirty/corroded connectors. After it pulls in during start mode, it should stay in until the key is turned completely off.

Also, the linkage has an adjustment range. It is possible that is incorrect and the solenoid cannot be electrically pulled in far enough to engage the latch. Momentarily turn the key to start, then leave it on run. If the solenoid did not stay engaged, manually engage it and see if it stays. Your previous test showed the solenoid can engage the latch, so if it does not stay now then you do not have 12 volts. If it stays, the solenoid was not pulling in far enough to latch.

 

[nightskyisme]

Regardless of the solenoid, it still doesn't start. I should mention the morning it didn't start, fuel was leaking from the fuel-bowl, so I removed and reinstalled it tighter, it then was fine....I did unscrew the bleeder screw and the lines coming out of the fuel-pump area and got fuel, should I have bled it more or somewhere else? Don't forget, I did get it started and it ran fine at maximun idle, just wouldn't idle and now doesn't start....any other things to check? Thanks again.

 

[JD755]

If you have an owner manual, it does describe the bleed procedure. There is one bleed screw at the fuel filter, then another one where the fuel hose enters the injectors. First bleed the one at the filter, then the one at the injectors. If that is not sufficient, the top nozzle nuts at each injector can be loosened and bled. Hold the bottom nuts in place while loosening the top nuts.

I still need to be clear on whether the solenoid is closing when the key is left on after an attempted start. If you check where the solenoid linkage connects, it is in the engine. So there will be no residual fuel in a line to keep the engine going briefly after an attempted start. The fuel is immediately shut off in the engine and it will die immediately.

Keep at it. We'll get this thing started!

 

[nightskyisme]

Ok, just came in from the garage.....the solenoid pulls in fine while cranking, but returns when I stop cranking (key still on)....good/not good? As for bleeding, since it won't run, I assume I loosen ALL the bleed areas or one at a time while cranking? Thanks

 

[JD755]

Nice thing about the 755 is you don't need to crank the engine while bleeding the fuel line. As long as the key is on, the electric fuel pump will run and provide fuel for bleeding. (The late model 855 and all 955 changed to a mechanical pump that does require cranking.) You need to bleed the line in sequence as the fuel comes from the tank. This means one point at a time. First at the filter, then below the injectors. Only after you have done those in sequence and there is still a problem would you need to open the top nuts at the injectors and bleed there. At each of the points open the line until fuel flows with no air bubbles, then close that point and go to the next one.

You do however still have a problem with the solenoid operation that needs to be fixed first. It is shutting off the fuel at the engine so it will never run. Disconnect the solenoid plunger from the spring loaded fuel shut off linkage. Turn on the key and push in the plunger. If it latches and cannot be pulled out then we can try resetting the linkage. But if it does not latch then you do not have 12 volts. You already tested the solenoid with 12 volts applied separate from the harness and saw it worked. This would be the same test but using the harness wiring. So if it does not latch we will need to check the tractor wiring.

 

[nightskyisme]

Well, I just bled the two screws on the fuel bowl and the one below the injector lines, all went well, BUT when I loosed the injector lines just above the last bleed screw on top of the fuel pump unit, nothing.....dry and no fuel....what gives there? (I even fiddled with the throttle and the solenoid) nothing...dry. I would assume there should be fuel coming out of those or does trhe engine actually need to be running for that?

 

[jd110]

Yes, the engine needs to be cranking to get fuel out of the injector lines. Since you are having fuel solenoid problems, try holding the solenoid in while cranking. You should see fuel spurting out with each revolution of the engine.

 

[nightskyisme]

Thanks, Ill try it