John deere 850 fuel pump - no output

[Chuck_L]

Good Day. Well I just joined up here. Having a problem with tractor I inherited dad; I hope I'm asking the question in the correct place. If not, please let me know.

Ok, the Tractor is a John Deere 850, late '80's. It has been running fine until few days ago when it started, ran for 20 sec, then died.

The fuel flows freely to the pump. But the pump itself just "spits" a little out of the three ports. The throttle linkage is fine. I removed the pump, did a little online research. I then dissasembled the pump. There is nothing in this mechanism that seems overly worn or suspect to the eye.

I am not experienced with diesel systems, but I am experienced with machinery in general. I am really quite flumoxed as to why this thing is not pumping out fuel. The pistons move freely. The check valves are pristine. The parts that make up the flow regulating mechanisms are, again, pristine. These three pistons are driven by cam lobes which are certainly still in the tractor and certainly still turning.

I don't see anything mechanically that says it shouldn't work. But it just stares at me, not working. So it's obviouly smarter than me.

Thanks in advance for any insight

Chuck

 

[beenthere]

Welcome to TBN
What "pump" are you talking about? The injection pump, or a different one?
Put up a pic or two and good help/advice should come your way.

 

[Chuck_L]

Thanks Beenthere, I'm uploading a couple of pics.
It is the fuel injection pump.

 

[beenthere]

From what little I know about injection pumps, you may have dived down that rabbit hole too quickly. But hope "thepumpguysc" member will chime back in, or you can seek his advice from other threads here, as to what to do next.
Hopefully the recovery is poassible, but I wouldn't count on it. Search for more injection pump information, and we will pray for you.

 

[thepumpguysc]

If u flip it over and go thru the bottom.. remove the pin, roller tappets.. PAY ATTENTION TO THE TIMING SHIMS UNDER EACH.!!
Then CAREFULLY lift out the pumping plungers..
Look at the “cut” (helix)..
If u see score marks, they’re bad..

 

[thepumpguysc]

When ur lifting up the plungers.. PAY ATTENTION TO WHICH WAY THE CUT FACES..

 

[Chuck_L]

Hello Pump guy. Well, I havent taken it apart from the back side. I removed "check valve" mechanisms from the front. I then took out the "cylinders" into which the "plungers" (I believe you are talking about) fit.

Yes, I became aware of the orientation of them as I was working with it. I was able to see (barely) that there is a kind of helical cut in them, and that was my "ah ha" moment where I understood how they regulate the flow.

Still, it sure seems odd that the tractor would run fine then suddenly not. I would think that if those plungers are suseptible to becoming worn, a person would notice having to throttle up the tractor more and more, as they wear and lose pressure.

Then again, maybe it just gets to a point where the presure is just no longer enough to get past the check valves... I guess I can see that happening in a more sudden fashion, so to speak.

Ok, well, I'll take it apart from the back side and get to those plungers and see what I see.

Thanks much for the tips.

 

[thepumpguysc]

Did u happen to see the slot on the barrels u removed.??
They HAVE TO SLIDE ONTO A LEAD PIN..
If u just dropped them in and tightened up the “top nut” u sheared the pins off..
U might as well stop now…
There’s nothing in the pump u can repair, other than a leak..

 

[gstrom99]

Welcome to TBN. It's rare for an injection pump to just quit. Like someone else said, you may be "premature" on the Dx. I know you said fuel "flows freely", but did you check/remove/replace the fuel filter first? Check all the hoses for cracks? Bleed the lines at the injectors?

 

[Chuck_L]

I hear you gstrom.

Everything is clean from the tank to the pump. No obstructions, no way for air to get it. The flow is smooth, bubble free, and strong.

Here is an observation: I disconnected the fuel line to the pump and removed the hollow bolt with the bleed screw. So at that point I was looking at the bare input orifice of the pump, with fuel all the way to the top of it. I cranked the engine and watched the level. It slowly decended as the 3 injectors "spit" tiny amounts of fuel out. This told me that something was amis, unless the system needed some amount of head pressure to keep things primed and pumping. So I reassembled everything, bled the lines, and used the exhaust port from a shop vac to put just a bit of pressure in the fuel tank and see if it would affect the situation in some way. However it didn't make any difference, better or worse.

But, thank you for confirming my suspicion; "It's rare for an injection pump to just quit." Now that makes sense to me.