Volvo 240 no fuel on one cilinder

[Dutch240]

Dear community,

I've got a problem with my volvo with the b230f engine.
I don't have fuel on the fourth cilinder.
Injectors are new with new o-rings
Al the injectors get 8.7 volts
Fuel pump works .
Temperatursensor has been replaced.
Fuel pump relais works.
If the engine runs on 3 cilinders you can hear the injector of the fourth cilinder working .
I am running out of Ideas.
The only thing that comes to mind is that the injection computer has a defect so it gives fuel at the wrong time so the engine can't Ignite it??
Please help
Wkr Jan