Ford 4600 SU engine vibration. Help!

My 4600 engine starts fast in cold weather and runs good overall but I do have one issue I'm trying to resolve. Engine runs smooth till 1600 rpms then feel a lot of vibration till 1800 rpms. After 1800 till max speed it's smooth. Any idea what could cause vibration 1600-1800? Injectors or fuel pump?

Thanks
 
Try cutting out the injectors one at a time while it's vibrating badly by loosening the injector line nut. If you find one cylinder that does not make a change in the way the engine runs, try swapping that injector with another hole and see if the problem stays with that cylinder or follows it to the other.
 
The nut where the fuel line attaches on the side of the injector. Just crack it about 1/4 turn or so. You should see fill spitting out past the fitting when you do this - don't be alarmed.

Do this one at a time. Tighten each one back up before loosening the next. Listen for a change in engine sound. Change in sound means that cylinder is firing.
 

I think there all firing but you tell me. Today I cut very heavy fescue down low and had the rear of the 6' bush hog 286 level to help shred the grass better. It did pull the engine down but I would think 2 cylinders wouldn't even touch that much grass. Thoughts?
 

When unloaded,, there is a speed where the engine will rock or oscillate. Probably an harmonic in the crank or balancers. Is that what your referring to? Could be the advance on the injector pump also as its advancing for a load and your not loaded.. So the engine will sound rough at that one rpm. If so, it pretty much on all fords...
 

Well I have a 4000 SU and it does it to but even worse and from 1800-2200 or max rpm. On the flip side I have a 2810 and 3910 and both are pretty smooth all the way through. Not as smooth as some of the Perkins and other newer stuff but nothing that bothers me either. But on my 4600 I find myself moving out of the bad rpm range to smoother waters so to speak. This is what was leading me to believe it might be something that could be improved.

Thoughts?
 
If the sound changed evenly on all 3, then I'm at a loss. Without being able to hear it for myself, I don't have any other thoughts. If it was a 4-cylinder engine, I'd have you check the balancer, but no such beast is on your 3-cylinder.

Can you give more details, like, is the engine loaded or not? Does it make a difference if there is a heavy load on the engine? Is the PTO on? Does the sound/vibration change when you step on the clutch? Do you hear any unusual noises while cranking with the fuel off?
 

Load seems to have little effect but sometimes under load it might be a tad worse. Pto on vs off is no different. Cranking with stop knob out presents no unusual sounds. Now I have posted on another thread a possible over heating issue toward rear of block near driver. Could a internal circulation problem cause this issue? Tractor seems to run well and cranks almost instantly in cold weather so engine seems pretty healthy overall.
 

I made a quick one but not sure how to post it. The funny thing is in the video the steering wheel is oscillating around. By the way when running the bush hog it is a little worse than with no load. Just seems to rough to be a normal condition to me. I'm thinking of putting in some different injectors just to see.
 

I had a mechanic review it yesterday and thinks the injectors need new tips. He will replace them next week so keeping my fingers crossed to see if it helps.
 

Guys, problem is resolved. Believe it or not I just ran two tanks of a heavy dose of injector cleaner and now she runs smooth again. I used Opti-Lube per a friends recommendation and to my surprised it worked. I will keep using the standard dose for protection.
 

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