John Deere 850 Started Running Rough and Blowing White Smoke

Matt Hightower · Jul 22, 2012

Hi all,

I have a 1985 John Deere 850 (3-cyl Yanmar diesel) with just over 1,000 hours. Today I was running the Bush Hog and everything was fine for over two hours of runtime (a little bit of smoke from the blow-by tube after awhile, but it was a HOT day.) All of a sudden in the middle of a pass it started running noticeably rougher and blowing white smoke. Not bellows, but it normally does not smoke at all. Now even after cool down it starts and runs quite rough and blows white smoke. If I idle down below 1k RPMs it dies. The smoke smells acidic (unburnt fuel) not sweet (coolant).

It has not leaked a drop of any fluid before. Now I have (literally) two drops of fuel on the shop floor and the middle injector is wet around the nut. The other two injectors are dry. The top of the gas tank is also wet, apparently from the return line.

I have limited experience with diesels, so would GREATLY appreciate any direction you guys can give as to what may have happened and how I can diagnose and fix the problem.

Thank you in advance!

Hightower

crashz · Jul 22, 2012

Maybe the injector line, nut or body cracked? It won't allow the injector to fire and would leak and run poorly. Just a thought.

arrow · Jul 22, 2012

It sounds from your description that you have an injector seal gone. As a result, this cylinder's fuel ratio is off in order for the engine to run properly. The injector itself could be cracked as well. Usually black smoke is unburnt diesel fuel and when an injector itself is gone, it throws too much fuel and doesn't necessarily leak to the outside. Start with the seal unless you can spot an injector breach. It will be alot cheaper this way if you could cure the problem with the seal.

Matt Hightower · Jul 22, 2012

Thanks guys,

Looking at it more, it appears that the leak is on the return line, so it would seem that the leak and the other issues are unrelated. I just got the thing. The previous owner replaced the injector pump and fuel lines less than 20 hours ago.

Any troubleshooting I can do before pulling the injectors and making the 50-mile (each way) trip to have them tested?

Thanks again!

crashz · Jul 23, 2012

Call the dealer first. The key words here are injection pump replacement. Sudden change in operation means something went haywire quickly and is not common for normal wear and tear. Seems to me, if you can be sure the leak is not a pressure line to the injector (check to make sure the nuts are tight), that timing slipped at the pump. Retarded timing will cause white smoke, as the diesel is not completely burnt. Will also cause rough running. I'm not positive that this is your problem, but its something to consider.

Jerry/MT · Jul 23, 2012

White smoke may be raw fuel. could be a burned valve or a burned piston crown. Is there any increase in the blow by from the crankcase vent tube? if so, check your compression.

What's the air filter look like? Is it clean? If it clogged you'll run higher peak temps in the cylinders and cause some distress.

Matt Hightower · Jul 24, 2012

Ok, so now I'm really confused.

I went down earlier to check the coolant level, the oil, etc.; all checked out fine. Nothing had leaked while the tractor's been off.

I fired it up and noted the same condition; rough running with occasional knock and white smoke with mild diesel smell from the exhaust. When I would idle down to 1k, it would erratically rev up and down. If I idled down further it would die.

After a few minutes though it started to clear up. It would smooth out a little then get rough again. Then got smoother. Still producing white smoke though.

I decided to put it in gear and see what it did under a load. At this point it was noticeably smoother, although still sending up white smoke.

After a few passes under load though, it seems back to normal; minimal if any smoking, smooth(er) idle, smooth throttle up and down, will idle all the way down to 750 rpm. It's still sending some smoke out the blow-by tube, but I can't honestly say if it's more than before or not.

What has me concerned now is, a) what was the problem, and b) why did it clear up in 30 minutes of runtime? I top off the tank every time I shut down, but other than that no fuel, oil, or coolant changes.

If it continues to operate "normally", is it safe to do so? I don't want to risk damage to the tractor.

Thanks for all of your input!

Hightower

arrow · Jul 24, 2012

Could be an air in the system coming from a leak or lack of purge when the injector pump was replaced. If so, it may have had to work its way out of the system. If it happens again I'd say its an air leak you are getting in your fuel system. Any bubbles in your fuel bowl?

tractordoctor · Jul 26, 2012

I've worked on tractors for 17 yrs at three different dealerships . Sounds like you have a bad injector . That model tractor unfortunately isn't an all true John deere . It's made a little cheaper , so you'll see problems like this arise from time to time . Just loosen the injector lines at about 1000 rpms one at a time you should notice a significant change in pitch . When the change is unheard or you don't have one make a big difference, then that would be your bad one .

arrow · Jul 27, 2012

tractordoctor said:
I've worked on tractors for 17 yrs at three different dealerships . Sounds like you have a bad injector . That model tractor unfortunately isn't an all true John deere . It's made a little cheaper , so you'll see problems like this arise from time to time . Just loosen the injector lines at about 1000 rpms one at a time you should notice a significant change in pitch . When the change is unheard or you don't have one make a big difference, then that would be your bad one .

The 50's series tractors were some of the best products JD ever put their name to. Yanmar arguably is one of the best small diesel engines in the world. If you meant "cheaper" as tractors with no frills, I can understand but JD spared no expense on the build of these tractors and I disagree as to why you see problems like this from time to time. I would agree if you stated the tractor was old, not used much, fuel related jelling problems, operator or repair errors but never to infer that these line of tractors have problems because they are cheaply made for they are not and I'd say this is more of an issue for some of todays products. The saddest thing about the 50's series tractors is parts availability is becoming scarcer and scarcer. They are too good of a tractor to succumb to obsolescence.