Detroit skip

pull your dipstick out and smell the oil for fuel.

blowby is going to smell like diesel. it's unburnt fuel from compression escaping past the piston rings.

 

I'd start by checking cylinder temps at the exhuast manifold. Most likely a broken valve spring, bad injector or the injector wiring harness. Use one of those infra red point and shoot thermometers. Could also be a bad cam or a bad cam follower, bull gear or a combination of all of these things. Start with the easy stuff...kinda sounds like a streaming injector. If you are flooding a cylinder with raw fuel then it should be cooler than the others as it cannot burn it all away through normal combustion so that cylinders exhaust will be cooler than the rest.

 

try to jump starter with ignition off. When motor crancks engine you feel compression of every cylinder. If cylinder is bad you feel and hear it. Use cheap chenese temp gun to find bad cylinder. After that remove valve cover to inspect exaust valves springs. It is not easy but possible to change spring w/o cyl head removing

 

bad injector caused the same on mine.puts fuel into the engine oil like snowwy said.don't run it too long like that please.

 

i had a dead cylinder. limped it 250 miles back to yard 5 cylinders. left the load behind.

came back 2 days later. problem fixed. oil level was much higher though. and you could smell the fuel.

dn't know what the problem was. but it was a cheap fix. changed the oil and truck ran better then before the problem so i'm guessing it was a overhead adjustment. jakes even worked better.

picked the load back up and delivered.