Diesel tractor revving up?

[M.Magis]

I don’t know much about diesel engines and have a small issue with one of my tractors I’d like to get tracked down if I can. It’s an ’86 JD 2550, 65 hp. Every once in a while, if I idle it down to get off and do something, it’ll increase the RPMs by itself. Say it’s idling around 700 rpm, it’ll rev up to around 2000. If I pull the throttle toward WOT, and then put it back down it’ll correct itself. It doesn’t happen all the time, and it just started this spring. I did have some major hydraulic work done that required splitting the tractor, they also dyno tested it. Not sure any of that is relevant, I mention it just in case. I’ve done some searching for ideas online, but most things I’ve found apply only to newer engines. Thanks for any ideas.

 

[M-5]

Fuel injector pump.

 

[hurleyjd]

Somewhere on the accelerator linkage you will find a place that has a friction washer there is good chance worn out look it over will real well most of the time it is on the rod that goes thru the dash and is about 2 to 2.5 in diameter. There will be a spring on the rod that keeps pressure on this washer to keep the speed you set.

 

[jltrent]

Fuel injector pump.

+1

 

[Nesikep]

While what hurleyjd says is the simplest, (and worth looking at), it really does sound like there's something amiss in the injector pump.

I'd add some 2 stroke oil (50:1 should help) in the diesel, along with injector cleaner.

 

[skyhightree1]

Fuel injector pump.

+1

+2

 

[M-5]

If you've ever ran a tractor out of fuel it will rev up just before it switches off. Its an unmistakable sound. if you kill it as soon as it revs you can usually get away with not bleeding the injectors

 

[M.Magis]

Thanks for the help. I’ll check the simple things first, but assuming it’s the fuel injection pump, is it something feasible for me to rebuild? Or am I better off just replacing it?

Edit: after a little reading online, I assume my best bet is to replace it or have a shop rebuild it.

 

[skyhightree1]

If you've ever ran a tractor out of fuel it will rev up just before it switches off. Its an unmistakable sound. if you kill it as soon as it revs you can usually get away with not bleeding the injectors

Yes and bleeding can be a not so nice word.

Thanks for the help. I’ll check the simple things first, but assuming it’s the fuel injection pump, is it something feasible for me to rebuild? Or am I better off just replacing it?

Edit: after a little reading online, I assume my best bet is to replace it or have a shop rebuild it.

Yea I wouldn't even attempt to rebuild one. Here a rebuild is about 600-800 from a good diesel shop

 

[hillbilly beef man]

My 2350 has did this for years. It is in the linkage, I just don't pull it all the way down, I just leave it just a hair above Idle.

 

[hurleyjd]

Thanks for the help. I’ll check the simple things first, but assuming it’s the fuel injection pump, is it something feasible for me to rebuild? Or am I better off just replacing it?

Edit: after a little reading online, I assume my best bet is to replace it or have a shop rebuild it.

Is it hard and slow to crank in the morning if so could have a air leak somewhere in the fuel lines.

 

[Nesikep]

I've taken a number of injector pumps apart and cleaned them and put them back together... You need a good workbench that you can have CLEAN, a few cans of brake cleaner and a bucket of solvent.. Take LOTS of pictures as you disassemble it.
I don't know what your mechanical skill level is, but if you're careful, it's not rocket science...

The basics of the injector pump are working, it sounds more like it's gummed up somehow, which is why I'd recommend fuel additives, though if Hillbillybeefman has had the same issue and it's in the linkage, by all means check that first!

 

[coalburner]

Had a Massey that would act a little strange like that, the manual fuel pump was full of trash. Almost like a plugged fuel filter. Also, we poured a quart of automatic transmission fluid in diesel tank to lube up injector pump??

 

[M.Magis]

I appreciate the advice. I'll try to look into the linkage this weekend. It doesn't happen often, so it may be a bit tough to diagnose.

Is it hard and slow to crank in the morning if so could have a air leak somewhere in the fuel lines.

Yes, it drags azz when it's cold/cool. Although, I understand that to be a common problem with these closed loop hydraulic systems if they have a leak somewhere. I hoped after having the trans pump and hi-lo rebuilt it would go away, but it's still hard to crank.

 

[greybeard]

There are several things that can cause it.
1. as stated, injector pump.
2. Most diesels use a spring of some sort between the rigid throttle linkage and the governor throttle input lever. Instead of the linkage moving the gov lever directly, the linkage puts pressure on a --this prevents mechanical damage to the governor and gives the gov a little time to react for a soft increase instead of a sudden lurch forward or stop during throttle input changes. If the spring is covered in oil, grease and dirt, (or a dirt dauber nest) the governor will 'hunt' when the throttle moves the governor off or on to the idle stop. Most gov springs are of the following type:
http://muellessmag.com/wp-content/uploa ... 015-15.jpg
3. Air or vapor in the system. Can come from anywhere, transfer/lift pump, tank shut off valve, even a back flow of combustion gas from an injector.
4. Water/condensation in the bottom of the tank or bottom of filter canister. As the injector pump gets a shot of water and sends it to the injector, the rpm drops and gov tries to compensate for the drop by suddenly increasing the quantity of fuel going to the injectors.
5. Broken injector rack idle buffer spring. Usually see an rpm 'hunt' (rpm surges up and down) if this spring is broken.
6. Partially plugged fuel filters.

 

[M.Magis]

Thanks Greybeard. This gives me a good list to look into. It hasn't done it this week, seems pretty random. I think the only time it's happened is when I idle down completely, so I'll check the linkage first.

 

[hurleyjd]

Try increasing idle speed to 825 to 875 per spec. Should be some stop screws on top of the pump that can be set to maintain idle desired. 700 rps is pretty slow.