Injector 4 doesn't squirt, get no signal from ECU

[Sensenmann]

Can somebody help me with this. I've swapped my engine for an M42, and the first start ( after 2 years .... ) was good. Running on all four cylinders. After 20 mins or so she started to run on just three cylinders.

I've checked the following:

- Sparkplugs ( even replaced them for new ones, and checked again for spark )
- Injectors, had them cleaned en they are 100% ok

The sparkplug from cylinder four was still clean after testing, so it is obvious to me that there isn't any fuel injected here.

Does anybody has some diagrams from the ecu so i can figure out what the **** is wrong here

Thanks for your support