My name is Glenn. Welcome to JustAnswer. I'd like to try to help you with this question.
From what you are describing, it doesn't sound like the glowplugs or the controller are at fault. The clicking of the glowplug controller is normal.
It is important to check fuel quality when experiencing problems of this type. Diesel fuel contaminated with gasoline will also cause this problem. A specificgravity tester is used by diesel mechanics to test this..
Once he gets it started, he keeps his foot on the throttle to keep it running... got that. After doing this for a few minutes, can he release the throttle without having the engine stall? If the engine is stalling, he may have a restriction in the return line that comes off the top of the injector pump.
You mechanic needs to remove the fuel return hose shown in the image above and to crank and start the engine. A small flow of fuel should be leaving the top of the pump from the fitting that the line had been connected to . If you put your finger over the nipple and block it, the engine will stall. If this line is restricted, the engine will continuously stall.
There have been problems with "fuel drainback" on this application. Air can get into the injector pump after the engine shut down. This is a result of age and wear at the fuel injection pump lever shaft.
This problem will require serious cranking to restart the engine.. The plastic caps on top of the injectors ( referred to as "fuel return tee" in the following image) that connect to the fuel return lines can also admit air to this system.
( by the way, even though I am showing a disassembled fuel injector, there are no field-serviceable items on this injector other than the TEE, the o-ring seals at the TEE, and the COPPER GASKET at the bottom of the injector)
Some technicians have tried raising the rear end of the vehicle way up in the air to keep the tank higher than the injection pump after shut-down to try to pinpoint this problem. Vacuum tests can also be done on the system to try to pinpoint this as the cause.
I'm not sure where you are getting those fuel pressure specs. If you are talking about the mechanical lift pump on this engine, it should show 2 psi at idle and 1 psi at 3300 rpm. It should be able to maintain 2 psi while cranking when tested at the test port .
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