I have a john deere 6400 with starting problems it turns over very slowly even with assistance of another battery it started for 15 seconds and cut out agin as soon as the jump leads were removed. There is smoke coming out the exhaust when its turning so ive cancelled out a diesel problem! I also have only the battery light on the dash panel nothing else works! Any help much appreciated!

I am unfamiliar with your exact product but can explain the operation of a Diesel on Startup.

The initial start requires glowplugs, a glowplug timer, and a power relay (which may be incorporated as a timer/relay combo unit}. Once the engine starts, compression fires the fuel after the cylinders heat up.

First, you need a strong battery. Then you need a good starter. Have both checked. A draw test on the starter can be done on the unit or use a bench check.

Check the power pulse to the glowplugs by using a Voltmeter on a disconnected glowplug wire. Note how long or if it works at all. If the wire going to the glowplug does not work, it is connected to the timer.
No power coming out of the timer can mean no power is going into the timer. That means to check the power relay supplying the timer first, before condemning the timer.

If all seems well, its time to pull the glowplugs and test them. As you can see, the time is brief. This means it is the only amount of time the glowplugs have to heat up.

Glowplugs can be checked by energizing each glowplug with a battery jumper cable and comparing visually the glow of each plug. The more each glows, the better the condition of the glowplug. BUT you can melt them. Be careful to preserve the threads of each glowplug by fixing the battery cable to the base housing and touching the top of the glowplug with the other battery jumper cable.

There will be arcing, but the top of the glowplug should still accept the feedwire after you do this. Darker glowplugs are worn out. Remember that heating time is limited.

NEXT, Some makers use a relief valve for "cold start" compression. I know Kubota does. This device is suppose to relieve compression for easier starts and may also be a possibility for your problems.

Please rate my info.

Several things may help here,,check oil levels and see if the oil is really thick(in cold weather it will turn to sludge and startup is almost impossible) heat the engine witha space heater for some time to warm it up if possible..or take a torch carefully to the block for some minutes..do not discolor the paint, just enough to warm the engine..also take the starter off and test for high end torque while free running..if not turning to speed replace it..( a warmed up engine will start easier)..then change to a lighter weight engine oil for cold weather use..usually rotella 5w30 will work fine..and put a suplement aditive in the fuel for cold start use..like cetane boost ita what truckers use in colder climates..we had a fleet of diesel trucks that wre a pain to start in below zero weather until we learned about the cetane additive and tricks for cold weather starting some years ago.. now most gas stations sell pretreated fuel for their area of the country.. this is a requirement by federal law...but the rule of thumb is a quart of cetane for a fifty gallon tank of fuel for anything between zero and 15 below temps ..above that a quart for 100 gallons should be fine..only use ether as a last resort..because too heavy of a concentration will blow the engine apart. this smoke is a combination of diesel fuel and engine oil vapors that have collected together in the combustion chamber during startup proceedures..but I think if you heat the engine for a bit with a space heater it will help to get things going for you.. and charge the battery also..repost findings thnx

Check and clean both the pos. and neg. cables . also give the battery a good charge.