35hp diesel lugging, dying under load

[petebert]

Tractor is Zetor Zebra 3520, 35hp diesel made by HMT. Under load the engine starts to lug, blow black smoke and will die. To get it restarted you have to pump the manual hand pump that you'd normally use to bleed the system. Thought it might have been the lift pump dying so I put a small 3-5gph electric pump inline before the lift pump, that doesn't seem to have helped. Should I have gone with a higher volume one or bypassed the lift pump?

Another thing I just noticed is some leakage/bubbling on the injection pump. It's a Bosch pump but so far I can't find a model number on it.

 

[kthompson]

Have you checked your air filter and the air intake system?

 

[thepumpguysc]

The pump requires 25 psi to run correctly..
The gov says "mico" which is Licensee of Bosch..
The name plate is above the side cover.
The "leak" should be oil.. no fuel in that area..

 

[thepumpguysc]

The lift pump/supply pump bolted to the side of the inj. pump should produce the sufficient fuel required..
All you did was install a "helper" pump to pull the fuel from the tank to feed the supply pump.. helpful? YES.
Is there a fuel return on the inj. pump?? Fuel comes in on 1 side.. then what?? does it return thru a "banjo bolt" style connection?
OR is it blank w/ a bleed screw.. your pic doesn't show the top of the pump..
IF it has a return.. then it has an overflow valve.. those valves get weak or break over time..
You can check it by removing it.. DONT take it apart if its the 2 pc. style.. Just remove it.. either shake it or use a small pick/scribe & poke the bottom.. it should have spring pressure on the ball or valve..
if you shake it.. your listening for it to rattle if it has a broken spring..
The symptoms of a broken/weak ovflo is> low power & hard starting..

The valves in the supply pump are "nylon" & they get beat down after awhile.. The rebuild kit for the sp is Bosch P#>DGK301.. OR.. a DGK301-H that includes a new hand primer.. The kit includes, 2 valves, 2 valve springs, & all the copper gaskets, new glass filter hsg bowl & nylon filter.. & w/ the "H", you get a hand primer..

 

[Agvg]

Take the pump off the injector pump and check that the piston is moving freely, but I suspect you have something in the tank or lines thats are blocking the flow of diesel.

 

[Agvg]

This is the old Zetor design with the tank higher than the pump?, it should por out diesel wen you remove the hose from the tank, you have checked that the valve under the tank is fully open?

 

[petebert]

Thanks, lots of info here. Lets see how much I can comment on right now.

Yes there's a fuel return, I can see it dump back into the fuel tank.

The fuel tank is above the lift pump and if you undo the line the fuel will all just drain out.

The tractor seems to start pretty easily it just chugs/lugs under load. For example I can drive it in 5 high, I can run the pto while sitting still. I can't drive and run the pto at the same time.

Here's an older video of it lugging, now if I where to get off and pump the manual pump it will get going again.

 

[petebert]

Here's a video I just made the other day. Notice the small amount of flow through the clear filter. Around the 10 second mark I start to use the hand pump and you can see a slight increase in flow. Not sure if this means anything.

 

[Agvg]

Would have rebuild or replaced the fuel pump, do you have fresh oil in the injection pump? New fuel filters?

 

[petebert]

Fuel filters are good. It's pretty hard to find parts for this tractor due to it not being a real Zetor but a HMT so I haven't been able to find a fuel pump. I had no idea the injection pump took oil, can you tell me how to do that?

Here's some more pics showing a better pic of the data tag if that helps. Also shows the fuel return line.

 

[thepumpguysc]

That return connector IS an overflow valve.. remove it & check it..
I'm not 100% sure if you have to add oil to that pump or not?? IF you do..the fill is on top of the governor hsg.
the big nut to the right of the overflow valve.. Its gonna be TIGHT.. just give it a couple of raps w/ a hammer 1st..
The FULL mark is that banjo bolt on the back of the gov.. where you saw bubbles coming from..
Theres something fishy about that whole pump set-up.. There shouldn't be a soldered connection on that gov... its supposed to be either a screw plug or an oil feed line.. NOT a soldered-up, oil feed line..
As far as the fuel connections go.. I'm w/ the others.. I don't think you have enough FLOW TO the inj. pump.. clogged screen in the tank maybe?
Or a collapsed rubber line??
If you can.. while your checking the ovrflo vlv.. blow back thru THAT LINE, back to the tank.. just to eliminate a clogged return line..
BE SURE to remove the fuel tank CAP before you do that.. or you'll pressurize the tank..
OH.. that's another thing.. The FUEL TANK CAP.!!! remove it & do your tests.. you might just have something as simple as a clogged vent in the cap.!!! They HAVE TO breath.. if you remove it AFTER running and you hear it sucking back down..vacuum.. that's it..
Good luck.

 

[petebert]

When you're talking about the valve, is it just this? There's a ball on a spring in there, wasn't stuck or anything. Moved back and forth pretty easily.

Also could this be part of the issue. These two bolts on the fuel filter housing. One of them is broken. It has just enough thread left to seal the hole. The hole is clean, there's no pieces of it left inside. On a related note, anyone know where to get a replacement? It's a specialty bolt, as you can see on the complete one it's got a hole through it. I'm guessing fuel passes through it.

 

[TnAndy]

Check the really simple thing first. Do you have good fuel flow from the tank ? Take the hose off at the tank and see what comes out. TWICE with my tractor a floating obstruction (in the tank) has decreased fuel flow from the tank to the point the tractor would barely run. Fuel would just 'dribble' out, but stick a skinny screwdriver up in the fitting, moving the obstruction aside, and you get HOSED with fuel.

If you're not getting enough fuel, it will act exactly like you describe. Idle fine, but can't take a load.

May not be your problem, but having seen it twice on mine....plus a Mitsubishi dozer I had, I'm inclined to look at the tank outlet first to make dang sure fuel is available.

 

[Agvg]

That is just a bolt for bleeding out air. Replace it with a std M6 bolt, the filters comes after the pump so it's not there your problem are, but do replace the bolt and seal because all minor leaks in a diesel system are a bad thing. If you want a proper bolt find a Zetor dealer.

 

[thepumpguysc]

Yes THAT IS the overflow valve.. it should have some pressure on the ball/valve.. you shouldn't be able to blow thru it from the bottom hole.
Like Agvg said.. just replace that bolt w/ a metric 6mm AND GASKET, don't worry about the holes.. you obviously didn't know what is was for, before.. {bleed screw}

 

[EddieWalker]

Make sure you have gone over the basics first. Then double and triple check to make sure you haven't missed something. Start with your fuel tank. How clean is it? Is there any debris in there? Metal tanks rust on the inside and flake of debris all the time. The location where the fuel line get the fuel can easily be blocked and when this happens, the tractor will start fine, but not have enough flow to get any power.

If your tank is clean, blow out or replace your fuel lines. Again,make sure you look at every inch of the fuel line. I use a compressor to blow out my lines and the results where significant!!!!!

Is there anything between your tank and that clear fuel filter? Anything at all?

Is there a screen or really small filter inside your mechanical fuel pump that you used to manually increase the flow of fuel in your video? Are you sure? On some tractors, it's the size of a large nut and easy to miss when it's dirt and blending in with the metal insides of the pump. When clean, mine is a copper color, when dirty, it's almost impossible to see.

What brand and how old is that electric fuel pump? Is it designed for diesel? Have you disconnected it and seen how much fuel it shoots out when on? I've replaced them on other tractors because of starting issues when hot, and can easily see a power issue if one wasn't putting out enough pressure.

You need a check list and you need to go at this one step at a time.

Good luck!

 

[thepumpguysc]

Good advice Eddie.. 1 thing I did notice is the location of the electric supply pump..
Its feeding the "manual/mechanical" supply pump.. "IF" theres a problem w/ IT.. then the electric one isn't going to do anything but feed a "problem".
The piston could be stuck or the spring could be broken.. VERY COMMON on those Mico pumps..
I would go directly into the inlet on the injection pump for diagnosis purposes..
& like you stated last {I think we ALL said it}.. what kinda pressure is the pump putting out.??? The pump NEEDS 20-25 psi to run correctly..
GPM don't tell me squat.. I'm SURE theres a conversion {google} but THAT should have been done BEFORE purchasing the pump..

 

[petebert]

Got the tractor working. Where the fuel supply line goes into the bottom of the fuel tank there's a fitting with a shutoff valve. I pulled the entire fitting out and it was plugged with crud. I blew it out with the air compressor and everything works fine now. So do I remove the electric pump now? The only benefit it would serve is priming the system, although this tractor can start pretty easily after sitting for a few months.

Here's the fitting

Flow rate looks much better now.

 

[mike48130]

Remove the electric pump and put on a diesel fuel filter. They should be vertical and have bleed screws on them to get the air out. Get one for a Ford or JD compact tractors. They are about the same and filters are availible.

I had a ford 550 TLb that did the same. It would act like it would run out of fuel about 1/3 tank left. Same issue with the clogged screen.

Check the simple stuff first.