ZD326s Bogging Down Under Load

[mmarkki]

I have a 2013 ZD326s with ~1500 that is bogging down under load. It starts and runs great in place, no smoke, no misfiring. It will drive okay forward but as soon as both levers are put in the fully forward position, the engine speed will slow down. When running the PTO, the problem is much worse and the mower at full throttle slows down to a crawl with the deck raised to 3". This happens on both tanks, right and left side.

What I've done so far:

1. Replaced both inline fuel filters.
2. Replaced the 12v fuel pump with an aftermarket unit for diagnostic purposes and checked for proper flow to the injection pump.
3. Checked air filter, radiator screen and proper fuel level.
4. Bled the fuel system at the injection pump and injectors.

At this point I am thinking of checking/replacing the fuel hoses but I would rather not have to tear the whole thing apart if the problem lies elsewhere.

Does anyone have any other ideas of what can be attempted before I take it to the dealer?

 

[GreensvilleJay]

junk in tanks.... it is 12 years old....
parking brake kinda on

 

[whatsupdoc]

You could bypass the fuel tanks with a small test fuel tank that would provide unrestricted fuel flow.

 

[JohnR68]

I don't know what the tank on the ZD236 is like but i had a similar issue on my old F2400. I changed the filters, treated for algae, cleaned out the tank, blew out the lines, tested the lift pump etc, and nothing helped. What i think might be going on is when the fuel level gets below a certain level, then when you load up the engine and increase the fuel demand, a vortex is setting up in the tank at the outlet and sucking air down the center. If I let the tank level get down below about 3 inches in the bottom, (I dip the tank because there is no gauge working on this old girl) I start seeing this happen. On the f2400 the outlet is just a hole in the bottom of the tank with a small stub welded on the outside for the flex pipe to clip onto. If I could get in there and put a right angle bend at the outlet I believe it might cure the issue.

 

[Russell King]

@JohnR68

If you have some sort of lift pump involved (tank mounted low) then that is probably failed. When tank is fuller there is enough static head to get the fuel to flow well to the injection pump, when low you basically run out of fuel at the injection pump.

 

[JohnR68]

@JohnR68

If you have some sort of lift pump involved (tank mounted low) then that is probably failed. When tank is fuller there is enough static head to get the fuel to flow well to the injection pump, when low you basically run out of fuel at the injection pump.

The tank on the F2400 is mounted high, the bottom of it is a little higher than the injector pump from memory. There is a cam driven pump immediately before the injection pump, I may not be technically correct in calling it a lift pump I'm not sure, but either way it seemed to be working ok to me. I didn't do more than a subjective test, just pulled the discharge line from the pump outlet and observed plenty of fuel there and felt it pressure up a piece when i blocked the outlet with my finger and activated the pump. You may well be right and that pump is worn but its not a big deal for me to keep the level higher than i otherwise might have. If it quits working with the tank level high i likely will investigate that pump a bit more though.

 

[whitetiger]

checked for proper flow to the injection pump.

How much flow do you have to the injection pump?
How many seconds does it take to fill a 12-oz water bottle?