JD 790, engine problems?

dfriesen · Mar 18, 2002

This is my first attempt after finding this forum from a Google search. I have been having problems with my tractor and trying to learn. I purchase a new 790 for several chores around the shop, Transmission Repair shop that is. I have only 1 acre to mow with rotary cutter, snow to remove with FEL and dead cars and trucks to move that have clutch and transmission failures. The problem is that this tractor runs rough, soots up the exhaust and requires 2-3 minute of idle time (1200 rpm+/-) to warm up and run on 3 cylinders. Dealer has had it in several times in the first 30 hours. I change oil every 20 hours due to the constant start up/shut off cycle here at the shop. I have continued to use JD break-in oil per dealer recommendations.

At 85 hours, the dealer asked if I would pay for the hours on the meter and take a brand new tractor - since they have found no solutions for the engine running so rough - related to the poor burning of the fuel. I agreed, and asked the dealer to do a 10 hour break-in on a dyno - because there is no way for me to put this new tractor under load, pushing in a few cars and trucks every day. The dealer had assumed that our start-up/shut-down cycle was the cause of the problem.

Now, new tractor with only 15 hours on the dial is running the same way. Now they say it must be my fuel. I have been doing this for nearly 30 years and have had 8n's, Gravely's, PowerKings, and for several years a JD 770 - the only other diesel. I have never heard of blaming the running issues on the way it is used. I did not have this problem with the 770 and my friendly competitor has had several similar small diesels including Kubotas, Yanmars and a Massey 1240, with no problems.
Any ideas??

CVHoss · Mar 18, 2002

<font color=red>I have never heard of blaming the running issues on the way it is used</font color=red>

Don,
I'm not sure that the reason you've been given is too far fetched. My purchase last year of the J.D. 4400 is my only venture into the compact tractor world. My previous tractor experience dates back almost 3 decades, so I'm not sure about the newer diesel engines, but I do know that with every tractor I've used before, I was always instructed to keep the engine at, or close to, the rated rpm range. I've been told that tractor motors are designed to work efficiently at basically their rated speed and that to run them at less was asking for problems. I'm not sure, but given the tasks that you list for your tractor, are you spending a good deal of the time at lower throttle settings? Also, you didn't say what you were using for fuel, but given that it sounds like the tractor gets limited run time, fuel cost shouldn't be a problem. If you aren't already, I'd suggest buying the best grade of on-road diesel (low sulfur content) available and adding a good additive to it (per recommendations from the TBN brain trust, I've been using Power Service and having good luck) and see if that doesn't help alleviate your problems. If it doesn't, at least your dealer can't blame it on the quality of fuel your using and should work at it until he finds what the problem is. I'm sure you'll get some more intelligent answers from others on the forum, but that's the limit if my experience.

Hoss

markcg2000 · Mar 18, 2002

I use my 790 for either snow-blowing or mowing at least half the time, so that means I have the RPMS's at max (recommended) a lot. I've never had an issue. I bet that you are having the problem because the low engine speed doesn't allow either the injectors or pistons really clean themselves out. Assuming, of course, that you are running top-grade fuel.

Might try letting the tractor run @ ~ 2000rpm for a minimum of 3-4 minutes each time you start it, wether at the beginning or the end of the move. If you're only running around the lot, can't be too worried about the fuel "wasted".

RoyJackson · Mar 18, 2002

After reading quite a few posts in the last months, it appears most of us don't normally run the engines at rated speed (which, I assume, is PTO speed) except for mowing or snowblowing. Other tasks such as FEL work or grading are at considerably lower engine speeds. Even mowing at PTO speed is for the efficiency of the driven implement rather then the tractor's engine.
There doesn't seem to be many others with issues as described by dfriesen.
Seems more like a fuel issue...do you get your fuel at the same place...if so, try another dealer.
There were two different tractors with the same problems. The only thing in common is the dealer, and, perhaps the fuel supplier. If it's the dealer..their setup on their tractors may have problems (i.e. dealer prep). If you get the fuel at the same place, they may have contanimation in their tank.

dfriesen, you did have a 770 Deere with no problems. How long ago did you sell that..or did you trade for the 790?

dfriesen · Mar 18, 2002

I was surprised how many there are that responded! I just found this forum when this problem arose and I was looking for answers. Thanks.

We have done a fuel sample, Cetane above 45, which is mid-range of what Deere asks for. The fuel is extremely low sulphur according to the dealer.

I did not experience any of these problems with my JD 770 in several hundred hours. I traded tractors on a whim and a few hundred (1850) dollars because the dealer said that my used tractor was nicer than the day it was delivered. Several coats of wax, frequent washings - it was spotless. The 770 had R-1 tires and they were worn more than 50% from the constant use on cement. The dealer trade and attitude has been unbelievably fantastic.

dfriesen · Mar 18, 2002

I purchase my fuel at a Texaco Truck Stop so as to have fresh and blended fuels for winter and back in the summer.

I had none of these concerns with the 770. My competitors down the street are both using Kubota's and seem to have no problems. They have both been up looking at my Deere, green with envy.

Dealer today recommended that we try again with the same fuel and Deere's own cetane booster.

dfriesen · Mar 18, 2002

I loved my 770. I had no problems with it in the exact same usage. I traded 18 months ago. The dealer tech has been in contact with the Deere factory tech support. They are now telling us that this engine, same as in the 4300 and 4310, is designed for variable engine speed usage. Unlike many diesel engines, our application should have no bearing on this problem.

I do agree with the Deere tech and others who have responded on TBN, that it seems as if the nozzles are not warming enough to clear. I do not however understand why that causes engine oil residue in the exhaust stack.