Combines 1640 losing Power

Had one fellow here with a 1480 doing similar. Had fuel build up algae in the tank so it got drained. He added amsoil diesel concentrate and he said in one hour it was back to normal. It cleaned the injectors back up like new instead of stuck open. Might be some other things to put in your fuel but you need to used something with the new diesel. You need to use something like this especially before storage or you will have a bad algae problem next year. https:__www.amsoil.com_storefront_adf.aspx

I see you mentioned changing air filters did you change the inner one. We had a 1688 it did the same as your combine we changed fuel and air filters but did not change the inner air filter. It was still a dog and smoked mechanic asked if we changed the inner air filter we did and that cured the problem

You mentioned it was a 5.9l. Better check the turbo charger. You will be looking at an engine job if it is bad and not repaired immediately. Pull the inlet hose off the turbo and check if the impeller has any play in it and inspect the blades.

Thanks for all the ideas everyone. We found the problem yesterday afternoon, the fuel pump was going bad. Changed the pump and everything is running well.