I have a 98 12v automatic. 258-9k, #100 fuel plate halfway way forward, pump turned 5 clicks. Intake, Exhaust, Fully built goerend.
Background: When I bought it with 250k it had zero smoke puffing out of the oil fill. I just checked for the first time after buying the truck after 10kmi. The only thing been done since then is the tranny and pump tune, and I had the oil changed once, the shop did it, I do not know with what. I checked recently when adding oil (mystic 15/50). It used a little less then a gallon over 8kmi. But i'm not sure if that's due to a slow leak or burning it. During cold weather (below 35f) (although it was in the teens earlier that night), it has trouble starting it will crank right up and die a second later, on the second attempt it starts up and idles very low, by the time I get out of the parking garage it is warmed up fine and idles at 750, and 600 in gear.
Blowby: after it is warmed up it puffs with the idle enough to plainly see. I checked underneath for the breather but couldn't find it and didn't see any smoke exiting below the truck, only out the oil fill. I did the cap test, it does not blow it off, it does not spew oil, I can barley feel it against my hand, after a long run, it does it a little out of the dipstick too. I recently fixed an exhaust leek right after the turbo by tightening the bolt, but it sill poofs a little, very very little, when revved. The oil pan is dry as a bone on the outside. Haven't looked into it much further.
But this is my daily driver/baby.
Please, any input, and redirect me if need be. I'm pretty concerned at this point.