V8 engine 3.6 no power and malfunctions

Hello.
Got another problem with my V8 engine.

I've been building a V8 engine in my old Vw t3 bus for some time and for a couple of days he's been giving some sounds.
So far, so good...

only the engine has a personal problem with me!!

Whenever I start the engine, it starts briefly, gives first short of second gas for 1 to 2 seconds and then goes to the normal idle speed. However, it goes out after a few seconds.
When I give something gas so that it runs on 2000 revolutions, then it always fluctuates at the speed. If I give it really gas that it should come on 4000 revolutions or higher, I hear in the engine and also in the exhaust only misignitions.
What I've already checked:

-New petrol pump and petrol filter installed
-Lambda probe replaced and tested, no difference
-Both distribution caps replaced with new ones
-Right ignition distributor replaced with reverberator against a new used
-both coils(primary and primary) - the secondary winding) and all ignition cables (between 5.7 and 6.2kOhm) measured -
-Zündkerzen are new and sparks also depends on all eight cylinders.
-estimated 20 times checked if the spark plugs and plugs of the injection nozzles are plugged in correctly
-Air flowmeters, throttle flap pots, etc. Idle stability valve installed in another V8, runs without any problems.
-Both injection mouldings are removed and engine is turned briefly, all 8 cylinders get petrol
-Control times checked.(set on Ot by crankshaft, distributor fingers stand on the markings, in the cylinder head the markings on the camshafts stand against each other)

Now, what else can it be? Slowly I am helpless.....
can it be that the engine no longer has full compression? But then he shouldn't run quietly in the stationary gas.
Today I wanted to drive him off the lifting platform, but I hardly made any progress because the engine has hardly any power. He just went out when he started.

Is the problem more due to the ignition, i.e. the spark or the injection, i.e. the amount of gasoline, the injection time,...
Is it possible to generalize that to the two points at all?

Hope someone can help me

Greetings from the Saarland