Do the key on three times code tests, reads out in odometer window. Displays DONE when last code is displayed.
Write down and post.
Pull an oil sample and send in to oil test lab for analysis diesel contamination in the oil.
Run a compression test and post results.
Post up all numbers on each injector.
Most likely leaking injector nozzle pintle/s, leak raw liquid diesel into cylinder 360d of rotation. One blockoff fitting is not enough to find multiple leakers.
Soak the injector nozzle ends in MEK or acetone overnight if you can't locate the leaker. Try injectors.
Do you smell raw diesel while cranking motor, injectors in?
You've stepped into the modern world of HPCR diesels, expensive. Be ready for parts price shock.
Cheap parts in these kill engines.
Once you have white smoke problem solved, these MUST had HD commercial fuel water separator and dirt filters. OEM factory tiny insufficient ineffective filter is an engine killing POS. Lubricity fuel additive 100% of the time.
What engine mods?
I don't smell raw diesel no. I get parts relatively cheap thanks to my commercial account at Diesel Performance Parts in Nashville. and as far as engine mods Im not sure besides some cheapo CAI the guy before me put on. I am not a huge "Modder". Although I have owned a duramax before and do believe a good tuner can be a great benefit which is why I got one. Other than that not really sure.