2006 chevrolet kodiak c5500 q

6.6 L duramax diesel, pretty sure its made by GM/Chevy.
or 8.1 vortec gasoline

 

Duramax is made by Isuzu. Probably needs injectors. The company I worked for bought a new one in 03 that ran great for almost 200K. Also bought a new one in 04 and it was in the shop every 20K miles for different injector issues.

 

Common issues with those are "stiction", it happens when over time sludge builds up in the plunger areas in the injectors. There are oil additives that will clean up a lot of the issues that the Ford and Gm diesels have with injectors, fuel additives wont do spit for it BTW. The injectors are HEUI or hydraulic electric unit injectors and use engine oil pressure and electric pulses to fire. Before taking it to a shop try doing a oil change and adding a oil treatment designed to cure stiction issues. The dealers and a lot of shops will just say you need new units without actually trying to free the plungers up, they make way more on labor and parts that way. If after a bit power does not return then take it in. Oh and fuel and air filters are cheap, change them when you do the fluids.

 

The 2 that I had, with the duramax 6.6L Diesel, had more power than they needed. I used to haul firewood and would gross 24,000lbs. I never had a problem with any of them and went 100Kmi+. They are fussy about fuel filters.

 

The duramax I had you could pull them out through the front or remove the dog house to get the back 4. I cant believe the engine has to be pulled to replace injectors.