Engine runs great when cold, but really rough when hot

[marndin]

Hi there

We have a Simplicity 4WD ride on mower and for the last 3 months it has been running rough after it gets warm. I have looked for fuel leaks but can't find any, I have changed the fuel filter but it's still the same.

Anyone have any suggestions where I should look next or any tests I can do to narrow it down?

Many thanks

Martin

 

[GLyford]

Pull the fan shroud and look for mouse nests over the cooling fins?

 

[DLTTrekkers]

Pull the fan shroud and look for mouse nests over the cooling fins?

look for loose intake manifold

 

[CobyRupert]

Also..
Fuel line that collapses when warm..?
Gas tank that doesn't vent...?
Choke that sticks? (Or is it fuel injected?)
Coil?

 

[marndin]

It's a diesle and injectors. It doesn't appear to be isolated to 1 cylinder. I cracked open each fuel line to the individual cylinders and it had the same loss each time. So I assume that's a fair way of proving that it's not a single cylinder?

 

[marndin]

Here's a couple of images:

The image on the left where you can see the three connections comming out of the housing. I presume that's the fuel pump? Is the bolt in the middle a bleed bolt?

The image on the right from above shows the three pipes going into the injectors.

Should/can I undo/loosen the centre bolt to bleed the whole system?

 

[aczlan]

Or a bad coil (if its a twin cylinder motor)...

Aaron Z

 

[DLTTrekkers]

Or a bad coil (if its a twin cylinder motor)...

Aaron Z

That senterbold....do not open it . Thats to adjust the fueling.

 

[marndin]

Thanks...

 

[ruffdog]

Would the fuel bleeding bolt be one of the banjo bolts on top of the pump? (fuel inlet or the one to the left?)

 

[woodlandfarms]

Did you check the air filter? One that is gummed up can be act as a choke....

 

[ruffdog]

....and check the air inlet to be sure it is clear from mud wasps etc.

 

[marndin]

Here's a video of what it sounds like - The pipes appear to be good. I have ordered some clear pipe in order to see whether there is air getting in to the system.

 

[marndin]

No blockage in air filter. I have even run it with no air filter and no fuel cap

 

[ruffdog]

It sounds like the engine is surging or hunting some too. I have to wonder if the shut-off solenoid is getting weak and barely holding the fuel open.

 

[marndin]

How would I check that?

 

[ruffdog]

Does your unit have a "water in fuel" light? Does it have a wire coming from the fuel filter? If so, read this:
https://www.lawnsite.com/threads/another-b-s-daihatsu-diesel-problem-scag.262693/

 

[marndin]

Does your unit have a "water in fuel" light? Does it have a wire coming from the fuel filter? If so, read this:
https://www.lawnsite.com/threads/another-b-s-daihatsu-diesel-problem-scag.262693/

It does and I was not aware of that. Thank you.

I have now run the engine without the fuel filter wiring connected. It started misfiring again after the same amount of time.

 

[marndin]

update: There is air entering the fuel system. Here's a vid showing the evidence to date.

Air entering and exiting Fuel Filter 3 - YouTube The lefthand side is going to the Pump. The RHS is from the tank.

If anyone could suggest the best place to start looking for the leak. I'd appreciate it. Thank you.

 

[ruffdog]

I see the fuel flow is intermittent going from the filter to the engine. Is the fuel flow good to the filter from the tank? I couldn't see it in the video. It seems there is no lift pump between the tank and the filter and the tank has 2 fuel lines going into it from the top. I'm thinking a fuel supply and a return line? Being that the supply line is all a suction line, any crack or bad connection (fuel to filter) would allow air to be sucked into the system. It might be time to pull the seat/fender and look at the tank siphon tube in the tank and supply line.