JD 790 won't turn

[2549]

A run down of what I've done:

Went to start the engine and it turned and turned but wouldn't fire. No biggie. It got below 32 the night before and I figured it would take a little longer. It stopped turning completely and the dash lights were out. Took the battery home and put on a trickle charger overnight. Next day, no luck. Dash lights still dead and it won't turn. Tried jumping with my truck and no change. Bench tested the battery and it was ok, about 70% capacity. Went ahead and got a new one. Still no change.

Pulled the fuses and fluke'd them. All good.

Started doing random continuity checks. Hot terminal to starter is good. Starter to ignition good. Fuel relay and starter relay are good (open on one set of terminals and about 50 ohms on the coil).

Found out when I take the key to start and check the starter to ground, it gets grounded. Did it twice. Measured volts with the battery in the circuit (dropped from 12 to 0) and without the battery (ohms went from open to ground) on the hot terminal.

More random continuity checks, the intake air element is low ohms to ground. I need to go back and get better readings. Does anyone know what the resistance of that element should be?

Each reading, I tried to use the same bolt as the ground point for continuity (no pun intended).

I found a wiring diagram in another thread. Awesome, by the way, thanks. Does anyone have a detail of the ignition switch and its contact tables?

Right now, I'm leaning towards a bad intake heater or an internal fault in the ignition switch grounding everything out. I'd like to confirm that, if anyone has details on those two components.

I may just pull that intake heater out and take a look at its internals, anyways. Happy Thanksgiving, everyone.

 

[beenthere]

Does anyone have a detail of the ignition switch and its contact tables?

Here is a test procedure for the ignition switch from the tech manual.

 

[kebo]

Are you saying that the new battery doesn't crank it over??? If so, it's rather odd that putting a brand new battery in made no difference. Are you sure the new battery had a full charge on it to start with??

I am going to assume before you actually try cranking it over that you are first switching the key to the "Preheat/Cold Starting" position? According to the manual for my 2001 model 790, the Preheat switch position is CCW (from OFF) although, it doesn't really define how long to leave it there before attempting to crank it over.

What year model is yours? Unfortunately, I am now about 70 miles from my tractor, otherwise I could make some similar resistance measurements to compare with. I'm in SC and mine cranked over just fine yesterday.

 

[2549]

I wasn't using the preheat, I probably should have. I just looked in my manual and it says 20 seconds for duration.

It's not the battery. Same dead indications with the old battery, new battery, jumped battery, etc.

beenthere, that page is great! Thanks.

 

[Tx Jim]

Sounds similar to typical bad/corroded batt ground connection. I would also recommend using the pre-heater at below 32 degrees after you get starter to turn engine over.

I'm curious what you think this has to do with the starter's ability to turn engine over and I'll quote you
[/quote]More random continuity checks, the intake air element is low ohms to ground. I need to go back and get better readings. Does anyone know what the resistance of that element should be?[/quote]

 

[RoyJackson]

You wrote you had no instrument lights...do you have headlights? Any lights at all? Trun the key to the run position (but not all the way to "Start"). Any lights?

Even with a low battery (unless it's totally dead), your lights should come on. Even with a safety switch acting up, your lights should come on (but the starter won't turn).

Have you tried jumping from your truck or car? Any changes?

At this point, sounds like a bad ground...or even a bad ground cable (off the battery). That would be the first place I'd look before any other disassembly.

 

[grsthegreat]

Did you check the MAIN bus fuse located near the starter???

its not in with the other fuses

if its not this...then i agree with Roy and others....its the ground. There has sure been alot of issues with every brand tractor concerning rust and ground wires lately.

 

[2549]

Well, it's been a little while, but I want to close the loop on this.

I ended up replacing the starter. Found the solenoid was shorted to ground. That's a problem, for sure. But, the new one would bench test fine, but wouldn't work on the machine either.

I jumpered 12V from the battery straight to the starter solenoid and it still wouldn't turn. I was still measuring continuity between the starter frame and negative pole and the starter hot terminal to the positive pole. It didn't make sense.

I replaced the battery side positive cable clamp and that did the trick. Fired right up. A little torquey with the new starter, too.

I'm still scratching my head at how I can have continuity between the starter and battery terminal, and not get it to turn. Dirty, intermittent connection, high impedance, blah blah. Maybe one fault cause a degradation and failure in the other. I don't know. All I know is it works now and I'm happier than a pig in...

Thanks again, for the assist.

 

[sunnyside360]

This is a more difficult problem to trouble shoot. I know because my neighbor had a near identical problem with his Case backhoe and asked me to look at it after he replaced the starter which did not fix it. To make a long story short the problem turned out to be a bad positive cable/connector. Replaced the cable assembly and problem was resolved and the machine has been fine for almost a year.

Good to see you are back in business again.

 

[grsthegreat]

This is a more difficult problem to trouble shoot. I know because my neighbor had a near identical problem with his Case backhoe and asked me to look at it after he replaced the starter which did not fix it. To make a long story short the problem turned out to be a bad positive cable/connector. Replaced the cable assembly and problem was resolved and the machine has been fine for almost a year.

Good to see you are back in business again.

my neighbor had a ford bronco with the same issue... took many hours to find