exe-file created by pyinstaller, not find self-defined modules while running

PyInstaller's official manual describes this issue:

Some Python scripts import modules in ways that PyInstaller cannot detect: for example, by using the __import__() function with variable data, or manipulating the sys.path value at run time. If your script requires files that PyInstaller does not know about, you must help it.

It also suggests what should be done in such a case:

If Analysis recognizes that a module is needed, but cannot find that module, it is often because the script is manipulating sys.path. The easiest thing to do in this case is to use the --paths= option to list all the other places that the script might be searching for imports:

pyi-makespec --paths=/path/to/thisdir --paths=/path/to/otherdir myscript.py

These paths will be added to the current sys.path during analysis.

Therefore, please specify the --paths argument while building the application. The manual states that specifying the -p argument is equivalent:

-p dir_list, --paths=dir_list

Set the search path(s) for imported modules (like using PYTHONPATH). Use this option to help PyInstaller to search in the right places when your code modifies sys.path for imports. Give one or more paths separated by ; (under Windows) or : (all other platforms), or give the option more than once to give multiple paths to search.

Also I had to fight a bit to get pyinstaller correctly import python scripts in a subfolder where the path to the subfolder was set relatively via sys.path.insert.

The answer by Yoel was correct for me but I needed careful setting of paths in Windows. Here is what I did:

My main py is:

D:\_Development\pCompareDBSync\pCompareDBSync\pCompareDBSync.py

My imported py is:

D:\_Development\pCompareDBSync\pCompareDBSync\py\pCompareNVR.py

(I have many of such imported py's in folder .\py\ but here i just use a single one as example)

So my main PY, I have the following include:

sys.path.insert(0, 'py')

try:
    from pCompareNVR import fgetNV_sN_dict
    from pCompareNVR import findNVRJobInDBSync
    from pCompareNVR import getNVRRecords
    from pCompareNVR import saveNVRRecords
    from pCompareNVR import compareNVRs
except Exception as e:
    print('Can not import files:' + str(e))
    input("Press Enter to exit!")
    sys.exit(0)

pyinstaller --onefile pCompareDBSync.py 

-> pCompareDBSync.exe that did NOT include py/pCompareNVR.py

I had to include the absolute pad to the main PY and the imported PY's:

pyinstaller --onefile --paths=D:\_Development\pCompareDBSync\pCompareDBSync\ --paths=D:\_Development\pCompareDBSync\pCompareDBSync\py pCompareDBSync.py

-> pCompareDBSync.exe that did now include py/pCompareNVR.py -> OK

And that solved this issue for me!