My 1994 Isuzu KB2800DT has a problem in that when it stands for a certain period of time, usually overnight, it gets air into the fuel line. It starts first time but after running for about 2 minutes, it starts surging and most of the time stops. If you operate the water trap pump you can feel there is air in and it gets hard again after 3-4 pumps. Any suggestions?

Check fuel pressure on the fuel rail and see what pressure is? If it is not OEM pressure, check the fuel filter first, that would be a cheap fix , if it is good then check the fuel pump!

Try using starting fluid. Available at Pep Boys and other stores.

Make sure no pressure on the fuel system before taking anything loose. Usually after the vehicle sits overnight w/o the key being cycled, there shouldn't be much pressure, but, you still need to be aware of possibility. Use a catch pan for any gas that might run out of fuel lines. Sometimes loosening the gas cap can help, sometimes it doesn't. If you think too much gas is running out of fuel lines, plug line till you go back with new filter. If new filter has arrow, the arrow points toward engine. Do the work in open air, not in a clos3ed garage where there might be pilot lite of some kind. If you use a drop lite be careful where you place it.
If the filter has threaded fitting on one end, use a couple of wrenches to take loose. If the other end of filter has a quick disconnect, some of these, I have taken loose with a pair of needle nose pliers.
As far as safely raising and supporting the vehicle, where applicable. Safety is your responsibility. Never use only a jack to support the vehicle.

I leased one of these, great truck. Some Fram fuel filters were recalled and the filters would leak at their connections. You could have a stuck fuel injector if your problem is mainly after parking it overnight or for long time periods.

There are some fuel vapor lines for the evaporative recovery system, but usually even a small leak will set a code.

Can't remember if the Lincoln truck version had a cabin air filter but if it does, the filter box may not be seated tight.

Sounds as if you have either a loose hose to the injection pump or a hole in the supply line allowing air to get in when engine is stopped. Check under vehicle after it sits to make sure you see any puddling of fuel. also inspect the lines going back to the fuel tank to see if you see fuel staining. Check the connections to the fuel tank to make sure they are sealed properly.

It could either be a fuel pipe between your prime pump and injector pump that sucks air so your diesel flows back into your fuel tank. Or you need to replace the prime pump.There is a rubber diaphragm in the prime pump that gets worn. Unfortunately need to buy a new prime pump. A simple sollution is to fit a non return valve to your fuel line. That need to be connected between the prime pump and fuel tank. Hope it helps. Blessings

If it's not working at all, it won't be delivering any fuel to the engine. When you crank the car to get it started, do you smell fuel? If not, try removing the fuel line (most cars this is easy to remove near the fuel filter). Put the unattached end of the fuel line in a container to catch any fuel that comes out. Crank the motor a few times. Any fuel? If so, the pump works (at least partially). If not, it's dead.

This routine varies by car and location of the fuel pump. Auto Zone usually has online repair manuals for free on their site. See if you can find one there.

Regulators are direct vacuum. they have to be in a port that is directly to the intake manifold. they can have other sensors in the line with them, but that line needs to be in the intake somewhere.

you will have to prime the fuel lines several times to get the air out of them. this is usually done by cycling the key off and on till you hear the diff in the fuel pump.

Is the line plastic or steel? They make repair kits for plastic lines, if you can find them. They are hard to find. If it is a steel line, you can go to the parts store and buy a pressure fitting. Cut the line and put the pressure fitting on. If it is the end of the lines, where they hook together or hook to fuel filter, it could be bad O-rings. Need more info.