jerking and shuddering engine ahfter speed80 km, also rpm working good up to speed 80 km after that drop down quikly and engine run up an dwon without actualy accerelation

 

To be of assistance we need a bit more information.
1. What model year and engine is your vehicle?
2. Have the OBD codes read and post the numbers.
3. When you say 80km is the engine rpm limited to 3000 rpm?

Get back with the information and we can proceed from there.

 

Lack of fuel?

 

yeah, this really sounds like a fuel problem. First thing I'd do, if I didn't have ability to monitor fuel pressure... is change the fuel filter because it seems the quickest and least expensive thing to do.

 

Is there a check engine light on? If so, could you maybe be in limp mode that maybe around the 80KM mark the engine RPM is about 3K? At that RPM is when the engine performance would be restricted.

Does the issue always happen at that same speed or could it be when the RPMS get around 3K? If it is the former definitely start with the fuel filter. If it is the latter you would have a code(s) associated with the check engine light. Then have the codes read and report what they are here and that would definitely help with teh diagnosis.