Cracking, loosening the Injector nut while the Engine is running if everthing is good you should have a noticable loss of rpms and the Engine should run rougher.

If you do that to a bad cyinder there would be little or no differance in the rpms of smoothnes of the engine running. In other words cracking/loosening the Injector Nut would not have much effect if there is a problem on that cylinder.

If you find a problem on one cylinder you then need to find out if it is the Injector or something internal in the Cylinder.

You do that by removing the Injector from the bad Cylinder and swapping it with one of the Injectors from the good cylinders.

Then you repeat the injector cracking test. If the problem now has moved to a different cylinder then you know it is the Injector.

If the problem after the Injectors were exchanged remained in the origional suspect cylinder then there is some interna engine issue or there is a fuel injection Pump issue on that cylinder. However, Fuel Injection Pump issues are rare.

If it turns out the issue seems to be internal remove the Valve cover and have someone crank the Engine by hand an watch what is going on in the valve train. You are looking for broken valve springs or other broken or abnormal stuff in the valve train.

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84 300D, 82 Volvo 244Gl Diesel