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.