L39 won't start, just buzzes

[lighthouse jim]

Suddenly a gremlin made its home in my tractor. After lunchbreak my L39 decided not to start. As soon as I turn key to On, I get a buzzing from relays under dash. Took dash apart, found the Engine Stop solenoid relay was the noisy one. It bench tested fine, so I checked the solenoid itself. tested not fine (compared Ohm values to my handy repair manual) so I replaced it. Same buzzing, but with that relay disconnected I checked for proper voltage at wiring harness connector-checked good. When I turned key on the glow plug relay started to buzz, but with a pulse that matches blinker. I jiggled the blinker switch to make sure it wasn't in On position, and buzz stopped pulsing but kept buzzing. bench tested that relay-checked good, and so is voltage reading at harness connector. I checked all ground connections (took them each apart and used electrical cleaner/corrosion cream) as well as + cable ends from battery to starter, (I reamed and cleaned these as well). Checked ECU connection for power-good. Took main switch apart to check for continuity-good, and got proper voltage at the harness connector. I bench tested Alternator for diode function-good. made sure battery is fully charged, and load tested it just to be sure.
It's been a long couple of days, and I've check this forum for advice repeatedly, and have checked areas where others have had issues. I'm running out of ideas. Help?

 

[Jim L.]

Buzzing as like the coil loads its field to hold in contacts, not enough juice, unloads and then tries again?

Somewhere there is a not quite good connection. If you put amps thru it there will be a voltage drop.

Do things get worse when the headlights are on?

It is also possible that a fusible link or ordinary conductor has broken inside the insulation.

You may have to make up some jumper wires to fault isolate the bad connection by progressively bypassing the circuit elements.

 

[lugbolt]

Funny story that is sorta relevant.

Guy brought me a Yamaha Rhino last week. Says it won't start just buzzes. He assured me that he's an electrician and says it's getting power to the starter, but it just won't turn over, and asks me to replace the starter. Ok no problem.

Replaced starter, still buzzes. Called customer. He says it must be the relay. Said replace it. Done. Still buzzes/relay buzzing. So now he's into it about $500 for the starter + labor + starter relay assembly. I grab my volt meter and test the battery. 12.27v. Load it down and it drops to 4.3v. Battery junk. Called customer and told him what I found, he says he's an electrician and knows that the battery is good. So I said it's ready to be picked up after some arguing. HE shows up about an hour later, says why won't it start. Told him the battery's too dead to crank it. Argue some more. I grabbed my trust jump box and hooked it up, fired the engine right up and drove it up on his trailer-after he paid his $570 bill, which could've been fixed by a $60 battery.

 

[lighthouse jim]

Thanks, Jim L. I’m trying to eliminate potential hiding places for that gremlin, and I like your idea of jump wire to help. Yes, the relay buzzes just like it’s not getting quite enough power, but last time I checked (was it only yesterday?) I forgot to check voltage at that relay while cranking...
I can hardly wait for morning, now. Thanks.

 

[lighthouse jim]

Thanks for trying to cheer me up, Lugbolt. I***8217;m stubborn enough to keep trying to solve this puzzle, but not stubborn enough to say I***8217;m good at it. (I did remember to load test the battery, though).

 

[thepumpguysc]

Just disconnect the solenoid, its just a push connector, & see if the buzzing stops.
The sol. is a weak link in that system.. I've replaced MANY..

 

[North Idaho Wolfman]

If very likely could be a safety switch (bad one) that is not allowing enough voltage to engage the relay fully.

 

[hope to float]

On my old girl I have to hold the forward/reverse lever lightly up to get the neutral switch to engage.

 

[lighthouse jim]

If very likely could be a safety switch (bad one) that is not allowing enough voltage to engage the relay fully.

I checked the seat switches (operator sensor and rotation) and both show good continuity according to WSM. The harness connectors show proper voltage. Is there something else? How would I check if a safety switch is allowing improper voltage through? ( I am getting full voltage at the relay end of the harness, so I don't know if this is really a factor, but I don't know how to check.)
Thanks

 

[re54drider]

You did not mention checking the negative cable/connections. A poor ground could cause this.

 

[lighthouse jim]

You did not mention checking the negative cable/connections. A poor ground could cause this.

Thanks for the reminder. It does sound like a ground issue, or a possible short. I checked, cleaned coated with anti-ox goop the grounds from the battery (both ends of the cable), ground strap on engine, and transmission. I tested the instrument panel connection ground pins, too, just for good measure.

I found a couple of mystery relays that don't show up on the WSM wiring schematic-on the right side near hydraulic pump-poorly taped from factory and full of dirt. Thought I'd found the culprit-used electrical contact solvent, tested relays(OK) and put it all back. Nope. Not it.

Any other ideas?

 

[lighthouse jim]

What symptom would show up if diode on starter relay is bad? I just tested mine and I'm wondering...

I tested with multimeter set at continuity-I should get open with leads in one position, and closed if I reverse them, right?
I get open in one, and different readings each time I switch- some times 1.2 , other times as high as 6.8 m ohm. Normal? Faulty?

 

[lighthouse jim]

What symptom would show up if diode on starter relay is bad? I just tested mine and I'm wondering...

I tested with multimeter set at continuity-I should get open with leads in one position, and closed if I reverse them, right?
I get open in one, and different readings each time I switch- some times 1.2 , other times as high as 6.8 m ohm. Normal? Faulty?

Well, I guess it doesn't matter too much--I just turned the key on with that diode in my hand and got the same angry buzz. Dang...

 

[D2Cat]

What's the voltage at the relay when you try to start the engine? If you jump 12v directly to the relay that's buzzing will the engine start? Maybe there's a ground on that relay that's not allowing full voltage.

 

[100 td]

What happens when you bridge/jumper the main positive battery lead on the starter motor to the starter motor solenoid spade connector? Does the engine crank at full speed. NOTE: Ensure tractor transmission is in neutral, park brake on and wheels chocked.

 

[lighthouse jim]

What's the voltage at the relay when you try to start the engine? If you jump 12v directly to the relay that's buzzing will the engine start? Maybe there's a ground on that relay that's not allowing full voltage.

I'll check this out-thanks.

 

[lighthouse jim]

What happens when you bridge/jumper the main positive battery lead on the starter motor to the starter motor solenoid spade connector? Does the engine crank at full speed. NOTE: Ensure tractor transmission is in neutral, park brake on and wheels chocked.

I haven't tried this. I'll check this out and let you know. Thanks.