Fuel pressure test

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First, you need a fuel pressure tester, they are cheap, go buy one!

Remove that 7mm little screw, fuel should come out, put some rag.

Hook the fuel pressure tester to the nipple.

Go in front, put the ignition key at ON, NOT START!!! do that 1 or 2 time to make sure the fuel pressure built up, go see the result in the back. Wait 15 min to see if fuel pressure drop. If it drop, you may have a leaky injector, a faulty fuel regualtor or a bad check valve in the fuel pump.  Also test the fuel pressure when the engine is running, the reading/difference is very small. You should be around 30psi. No real variation with RPM change.

To find if 1 or 2 injector areleaking you will have to remove injector rail (both, left and righ of engine) and look at the tip to see if they are leaking.

Most van do leak a bit, I mean if the pressure drop very slowly, it's ok. It may be a lazy fuel pressure regulator or a fuel pump check valve. That is not a big problem.

If no injector are leaking, the fuel pressure regulator may be faulty. No way to test this one easily. Heavy black smoke is a sign of a faulty fuel pressure regulator.