L4240 Stalls when the ambient temp is hot.

[bullockcm]

Pretty sure there is no lift pump on the 40series. Gravity feed all the way to the filter.

There absolutely is a lift pump on the 4240, not sure about all the other 40 series. It is vacuum operated not electrical as speculated earlier in the thread. I know this because mine failed just before the warranty was up but the issue was misdiagnosed by the dealership which led to a multi month debacle after their "fix" involved taking the high pressure injection pump out of calibration. All for what should of been an $18 part at that time and about an hour to troubleshoot and replace. I'll spare you the long version of the story but I'm no longer as ignorant about diesel engines as I was prior to then.

I do agree the rather common input shaft seal failure requiring splitting the tractor is likely unrelated to the stalling issue. The stalling issue is very perplexing as the ambient temp of ~ 80 degF is really not that warm and stalling from ambient temp and not machine temp isn't something I can recall ever hearing of.

 

[Jerry/MT]

There absolutely is a lift pump on the 4240, not sure about all the other 40 series. It is vacuum operated not electrical as speculated earlier in the thread. I know this because mine failed just before the warranty was up but the issue was misdiagnosed by the dealership which led to a multi month debacle after their "fix" involved taking the high pressure injection pump out of calibration. All for what should of been an $18 part at that time and about an hour to troubleshoot and replace. I'll spare you the long version of the story but I'm no longer as ignorant about diesel engines as I was prior to then.

I do agree the rather common input shaft seal failure requiring splitting the tractor is likely unrelated to the stalling issue. The stalling issue is very perplexing as the ambient temp of ~ 80 degF is really not that warm and stalling from ambient temp and not machine temp isn't something I can recall ever hearing of.

A "vacuum operated lift pump..." on a diesel engine! Where's the vacuum come from? Do you have a separate vacuum pump?

 

[5030]

A "vacuum operated lift pump..." on a diesel engine! Where's the vacuum come from? Do you have a separate vacuum pump?

Operator sucking on the fuel line maybe????

 

[rScotty]

There absolutely is a lift pump on the 4240, not sure about all the other 40 series. It is vacuum operated not electrical as speculated earlier in the thread. I know this because mine failed just before the warranty was up but the issue was misdiagnosed by the dealership which led to a multi month debacle after their "fix" involved taking the high pressure injection pump out of calibration. All for what should of been an $18 part at that time and about an hour to troubleshoot and replace. I'll spare you the long version of the story but I'm no longer as ignorant about diesel engines as I was prior to then.

I do agree the rather common input shaft seal failure requiring splitting the tractor is likely unrelated to the stalling issue. The stalling issue is very perplexing as the ambient temp of ~ 80 degF is really not that warm and stalling from ambient temp and not machine temp isn't something I can recall ever hearing of.

Well that is interesting. There actually are some tricky ways to get a little bit of vacuum from a non-turbo diesel intake manifold - or from any airflow. I think some Mercedes did some of that. It might just be enough differential pressure to work a tiny lift pump. And your L4240 does happen to be from those years (2007 to 2013) when Kubota was experimenting with innovative intakes trying to beat the Interim Tier IV emissions requirement.

I know about weird intake mods because we have a 2008 Kubota M59 from that same era. It came with the most bizarre EGR setup I've ever seen. This EGR is a technical marvel involving a water cooled muffler and a device cantilevered off the back of the engine block with some extra intake manifold valving whose operation varies with coolant temperature - as well as a couple of pages in the shop manual dedicated to explaining how it is supposed to operate. BTW, thanks to Kubota for those pages; they saved me from having to take it apart to figure out what was happening in there...

So a vacuum operated lift pump in a Kubota from those years would be just strange enough to be in keeping with what they were doing back then.

If any of this is real - and there really is a vacuum lift pump - it might simply need a replacement vacuum hose.
Luck,
rScotty

 

[bullockcm]

Well that is interesting. There actually are some tricky ways to get a little bit of vacuum from a non-turbo diesel intake manifold - or from any airflow. I think some Mercedes did some of that. It might just be enough differential pressure to work a tiny lift pump. And your L4240 does happen to be from those years (2007 to 2013) when Kubota was experimenting with innovative intakes trying to beat the Interim Tier IV emissions requirement.

I know about weird intake mods because we have a 2008 Kubota M59 from that same era. It came with the most bizarre EGR setup I've ever seen. This EGR is a technical marvel involving a water cooled muffler and a device cantilevered off the back of the engine block with some extra intake manifold valving whose operation varies with coolant temperature - as well as a couple of pages in the shop manual dedicated to explaining how it is supposed to operate. BTW, thanks to Kubota for those pages; they saved me from having to take it apart to figure out what was happening in there...

So a vacuum operated lift pump in a Kubota from those years would be just strange enough to be in keeping with what they were doing back then.

If any of this is real - and there really is a vacuum lift pump - it might simply need a replacement vacuum hose.
Luck,
rScotty

I am always up for learning and appreciate your response Scotty. Perhaps the more knowledgeable posters can help out here. Item 090 in the L4240 parts diagram below, "Assy pump, fuel". In my paperwork from the repair it is listed as a vacuum lift pump, if not powered by vacuum I am legitimately curious as to the drive mechanism. I do see the part is approaching $200 which is a far cry from the $18 listed on the repair invoice.

 

[alexpops]

I think the "vacuum" is referring to the fact it Pulls fuel to the motor/injection pump from the tank via rotating vanes or a diaphragm, as opposed to pushing it from the tank to the motor. The diaphragm/vanes are driven by either gears or a lobe from either your crank or cam. Some older gas cars had a spring-loaded arm that was moved by a cam lobe. I can't really tell from the resolution, but ... from the pics, the assy labeled 1G896- 52030 MAY have a button on the end that gets moved by a cam lobe. Assy 17121-52033 looks like a flat tab that fits into a slot on some gear -- maybe the same one that drives your high-pressure pump since it looks like it attaches below your injector pump. (look at the non-fuel line sides that need a gasket on the block connection to see if it's a spring loaded button or a flat tab that rotates)

 

[RjCorazza]

I think the "vacuum" is referring to the fact it Pulls fuel to the motor/injection pump from the tank via rotating vanes or a diaphragm, as opposed to pushing it from the tank to the motor. The diaphragm/vanes are driven by either gears or a lobe from either your crank or cam. Some older gas cars had a spring-loaded arm that was moved by a cam lobe. I can't really tell from the resolution, but ... from the pics, the assy labeled 1G896- 52030 MAY have a button on the end that gets moved by a cam lobe. Assy 17121-52033 looks like a flat tab that fits into a slot on some gear -- maybe the same one that drives your high-pressure pump since it looks like it attaches below your injector pump. (look at the non-fuel line sides that need a gasket on the block connection to see if it's a spring loaded button or a flat tab that rotates)

That's exactly how my filter's vacuum gauge is designed to work. A positive displacement lift pump creates vacuum drawing fuel through the filter, through the lift pump, and under low pressure to the injector pump.

 

[Jerry/MT]

I think the "vacuum" is referring to the fact it Pulls fuel to the motor/injection pump from the tank via rotating vanes or a diaphragm, as opposed to pushing it from the tank to the motor. The diaphragm/vanes are driven by either gears or a lobe from either your crank or cam. Some older gas cars had a spring-loaded arm that was moved by a cam lobe. I can't really tell from the resolution, but ... from the pics, the assy labeled 1G896- 52030 MAY have a button on the end that gets moved by a cam lobe. Assy 17121-52033 looks like a flat tab that fits into a slot on some gear -- maybe the same one that drives your high-pressure pump since it looks like it attaches below your injector pump. (look at the non-fuel line sides that need a gasket on the block connection to see if it's a spring loaded button or a flat tab that rotates)

The parts picture is a diaphragm pump that is actuated by a cam lobe that presses against a plunger that pushes against a diaphragm. There are check valves in the pump that allow fuel in on the intake stroke and then close when the fuel is pushed out the other check valve and toward the IP.

 

[rScotty]

The parts picture is a diaphragm pump that is actuated by a cam lobe that presses against a plunger that pushes against a diaphragm. There are check valves in the pump that allow fuel in on the intake stroke and then close when the fuel is pushed out the other check valve and toward the IP.

I believe ou are describing a positive pressure pump, not a vacuum pump. Either will work, although the vacuum type is limited by how high it can pump compared to a positive pressure type. Also, it is unusual to use vacuum pumps on fuels because it causes outgassing from the liquid.

 

[Jerry/MT]

I believe ou are describing a positive pressure pump, not a vacuum pump. Either will work, although the vacuum type is limited by how high it can pump compared to a positive pressure type. Also, it is unusual to use vacuum pumps on fuels because it causes outgassing from the liquid.

????
A diaphragm pump creates a small vacuum on the intake stroke to suck fuel in, then a check valve on the inlet closes as the diaphragm moves in the other direction to create a positive pressure (~4.0 to 4.5 psi) and the outlet check valve opens to port fuel to the IP.
The "vacuum pumps" I'm familiar with are used to pull air out of a tank, etc.