think it might be the fuel pump have cleaned fiter air.. replaced fuel filter temp doesent rise above 190.. can u put a manual pump on these? oil level good ..

What model Onan is it? A DKD ? an HDKAJ ?
Check the fuel pump pressure with a good gauge 7 - 15 psi should be fine, and check the flow by jumping the fuel pump to 12 VDC and let fuel run into the bucket. The stream should be a good steady one not a little pulsating spit. Disconnect the fuel inlet line from the genset, connect the genset fuel in to a source of good clean diesel (aka Bucket) and see if it runs ok then. Low fuel pressure always causes the diesel to emit a blueish white smoke. If it runs fine then you either have a porous (cracked) fuel hose or line or trash has plugged the dip tube in the tank, which a quick burst of shop air will clear up. With the pump jumped you should hear a slight pulsing sound. If it is clacking or otherwise noisy, it is drawing air. If you get me the model number, I will see if I can get the diagnostic page from the Onan manual to you. They are all encrypted but maybe I can cut a paste a page.

Billy T