4120 Fueling Problem Solved

[GalwayBoy]

I've been having ongoing engine issues with my 4120.
(Tractor is @ 39 months and 660 hours)
Engine will sputter at times, then come back up to speed.
Often seems like it's down on power.
Today it was warm enough (38) to actually go out to the barn and find out why.

Checked the fuel return line to the tank - nothing but a dribble.
Hmmm. Filter was recently changed. Possibly a gelled filter? I'm using winter fuel with P/S added. Pumped the primer, to find fuel @ the outlet.
Checked for flow @ the filter inlet while cranking the engine- nothing at all.
Checked for fuel @ the transfer pump inlet, and had flow from the tank.
Pulled out the transfer pump to find that the plunger rod is stuck, and will not return from the pump.

I used some #600 paper and was able to get satisfactory movement of the pump rod, and put it all back together. Tractor now runs as it did when I bought it. Not even a hiccup.

The odd thing was that throughout this ordeal, the fuel primer would bring fuel up to the filter, but would never get hard. Nor would it feel hard with the engine running.

It appears that the integrated injectors were drawing whatever fuel was available, thereby acting also as suction pumps?

I don't know exactly how long this has been going on, but my machine hasn't felt quite right for months. I'm happy to have figured it out, and happier still that it's not the injectors.

Now how a pump with 660 hours siezes is a mystery to me.

Jon

 

[kennyd]

Glad you found the trouble

Now how a pump with 660 hours siezes is a mystery to me.

Water, or another contaminate in the fuel would be my guess

 

[GalwayBoy]

Glad you found the trouble




Water, or another contaminate in the fuel would be my guess

Kennyd,
The pumping mechanism worked (works) fine. It was the push rod that became stuck.
The rod is totally outside the fuel area. It's bathed in engine oil, which is regularly changed per the schedule with Rotella synthetic.

I just started it upon my return from work, and it's still good.
Sounds different now too- That loud Powertech "crack" is back. The engine sounded somewhat muted when it was starving for fuel.

Jon

 

[RalphVa]

Glad you found the problem.

Fuel gelling is just wax formation. Melt the wax (and the 38ish weather would probably have done it), and it no longer gels. That apparently was not your problem. You can solve either a wax gelling or water freezing problem with a hair dryer blowing along the fuel line to the filter and on the filter itself if you ever suspect those might be the problem.

Ralph

 

[AKfish]

Kennyd,
The pumping mechanism worked (works) fine. It was the push rod that became stuck.
The rod is totally outside the fuel area. It's bathed in engine oil, which is regularly changed per the schedule with Rotella synthetic.

I just started it upon my return from work, and it's still good.
Sounds different now too- That loud Powertech "crack" is back. The engine sounded somewhat muted when it was starving for fuel.

Jon

Good bit of "mechanical Detective work"! Like to hear about those PITA mysteries when the solution comes out - thanks.

The rod must have gotten a veneer or residue of some kind adhering to the surface. Nearly 700 hours in 40 months. Doesn't seem like your tractor is sitting in the shade for real long periods..
Or the rod may have manufacturing defects and with use, there's enough "out-of-tolerances" that it's sticky..

Nonetheless, you nailed it!!

AKfish

 

[Treeman999]

My J D 4120 had the same problem. It has been going on for several years. I bought a new filter assembly first. Did not help much. Once you got it going it would run with an occasional sputter. Thanks to your post I replaced the fuel transfer pump and that fixed it.:cool2: