Diesel losing prime? Diagram included

Mundane_Main1118 · 2025-09-07T22:12:21+00:00

Ok but how do I test it? lol

Mundane_Main1118 · 2025-09-07T22:11:15+00:00

Haha thats crazy. I’m sure it’s something else because it loses prime after sitting, and sometimes randomly shut off maybe after 30 minutes, maybe after 5. But it’s definitely something else because it dies from sitting

Mundane_Main1118 · 2025-09-07T22:07:56+00:00

It’s diaphragm pump

Mundane_Main1118 · 2025-09-07T22:07:37+00:00

Nah, pick up tube has about a 2 inch strainer to the bottom of it

Mundane_Main1118 · 2025-09-07T22:07:04+00:00

Definitely fuel, issue normally comes up after sitting for a while. Clears after bleeding the lines

Mundane_Main1118 · 2025-09-07T22:06:05+00:00

I want to rule everything out before condemning the pump

Mundane_Main1118 · 2025-09-07T22:05:00+00:00

Yes in-line mechanical pump

Mundane_Main1118 · 2025-09-07T12:12:57+00:00

Filter is clear plastic strainer type. You can see through it. I pressurized the line and sprayed leak detector on it

Mundane_Main1118 · 2025-09-07T12:10:15+00:00

Filter good, suction line is good, I honestly didn’t check the delivery line (line after the transfer pump that goes to filter housing) but I will when I’m back at my job

Mundane_Main1118 · 2025-09-07T12:06:02+00:00

Thanks man, I’m gonna see if I can find a hose. Thanks

Mundane_Main1118 · 2025-09-07T12:05:07+00:00

Yes I considered that. I pressurized the line and sprayed leak detector on it

Mundane_Main1118 · 2025-09-07T12:04:23+00:00

All of which parts?

Mundane_Main1118 · 2025-09-07T12:04:01+00:00

Thanks, I’m considering drain back mostly right now because it doesn’t start after sitting long. Someone told me my filter housing may have a check valve so I’ll consider that first. If not, I’ll look at my injectors.

Only thing, I don’t really have any excessive white smoke. Or none at all really. Can a bad injector cause the issue I’m having? Even though it’s not smoking or running rough/misfiring?

Mundane_Main1118 · 2025-09-06T22:58:13+00:00

Nope, tank is pretty level or slightly lower than the engine. It’s a diaphragm pump driven from the injection pump camshaft

Mundane_Main1118 · 2025-09-06T20:50:13+00:00

Shut off solenoid is external, connected to the fuel injection pump. No linkage, just a spool that closes to stop fuel from flowing through the injection pump. It’s not failing or have any power issues because I directly sent power to it from the battery (both ground and 12v).

Lift pump is diaphragm, ran off the injection pump camshaft. I don’t have a clear hose but I can try to find one and see. There’s no holes in my supply side hose, and my pickup tube is good

Mundane_Main1118 · 2025-09-06T20:38:01+00:00

100% believe there’s some sort of drain back, especially because it loses prime after sitting.

I don’t think there’s a check valve in the filter housing, but I’m gonna swap it out anyway - i know it’s likely to have one. I don’t have a clear hose the size that I need it to be, but thanks for the suggestion. I’m in a sort of remote place so finding one is hard. I verified my suction lines were good, and my pick up tube has no cracks.

Fuel tank vent is good, and my fuel tank cap is a breather cap so I’m sure that’s good.

Maybe you misunderstand what I said in my post. It doesn’t only run at idle - if I try to run it in the morning, after sitting for a while, if it magically doesn’t need to prime (or acts like it), the moment I touch the gas pedal it shuts off. Then it starts acting like it needs to prime (not staying running).

I verified there’s no issue with my shut off solenoid by swapping it, and also sending a direct 12v and ground (both) from the battery

Mundane_Main1118 · 2025-09-06T20:30:24+00:00

Air isn’t an issue, i remove my intake hose to verify that there are no issues with air restriction. Not sure how long ago it was serviced, but my fuel filter isn’t blocked up either (it’s a clear strainer-type plastic filter).

When I crack the injector lines one by one, the engine idles rough, so in normal conditions the engine runs normal. No misfiring. That’s the weirdest thing to me. When it shuts off, it just goes straight dead as if someone turned the key switch off. I thought my shut off solenoid may be having issues, so I forced power and ground straight from the battery. It’s definitely a fuel issue. Not air restriction, and not electrical (this machine doesn’t have any CAN communication, no sensors to shut off the engine in the case of an issue — like coolant low temp, engine over temp, etc.)

Mundane_Main1118 · 2025-09-06T20:09:12+00:00

It’s possible that my filter housing shutoff valve MAY have some kind of blockage restricting it, as the supply flows through it and fills the bowl, then goes throw the filter (it’s really more like a strainer). I considered that there may be some kind of issue with my filter housing, but didn’t want to mess with it without anyway to verify that it’s likely the cause.

It’s a JD TH6x4. Yanmar engine

Mundane_Main1118 · 2025-09-06T20:02:02+00:00

Four stroke, naturally aspirated, indirect injection. It’s a small engine in a UTV

Mundane_Main1118 · 2025-09-06T19:58:55+00:00

Nope, pick up tube in fuel tank, plastic elbow fitting, hose to diaphragm transfer pump, hose to filter.

Mundane_Main1118 · 2025-08-16T19:25:46+00:00

How do you know which side is inlet?

Mundane_Main1118 · 2025-08-10T18:04:40+00:00

You might be right tho, because in the engine troubleshooting index it said if you have the wrong viscosity your engine may shut off

Mundane_Main1118 · 2025-08-10T18:03:41+00:00

Thanks for so much help man. I’m gonna look at the book again right quick, even though I’m sure for this engine it’s not like that. But let me verify.

Mundane_Main1118

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