Isuzu 1.8 Diesel does not start

Hi everyone, can anyone help me? I have an Isuzu 1.8 diesel and it won't start. I've already checked the glow plugs, injectors, timing, fuel, etc., but it just won't start. What I've noticed is that it's not getting much air through the intake manifold when I try to start it, but I've never actually checked how much air it drew when it was running properly, so I don't know if that's wrong or not. If anyone has any other ideas on what to try, I'd appreciate it. Thanks to everyone, I hope someone can help me.

Have you checked the pump's stop solenoid valve? And removed it?

I haven't removed it yet, but I feel like it's working when I turn the key, and it also emits a little smoke when I start it. I'll remove it to double-check, though. If you have any other ideas, I'd appreciate it. Thanks for your input. Regards.

These engines tend to have valve lag; check the valve adjustment.

Good afternoon. Try checking the compression of this engine. This will tell you if it's low. If so, put a drop of oil through the injectors and measure the compression again. This will help you determine if the problem is with the cylinders or the valves. If this is correct, try spraying a small amount of starting fluid into the intake. This should at least cause it to smoke. Look for the engine manual and the manual for the Opel Monterrey, which uses the same or an identical engine. Good luck!