08 Frontier Random Misfire and white smoke

Hey guys, is there anybody familiar with Nissan engines that can help on Diagnosing possible issue and repair for my old truck that has been sitting in my drive way for 1 year now. I want to fix it and give it to my sister or just sell it.

Truck is a 2008 Nissan Frontier with the 4.0 V6

Before I stopped using it, I had 2 out of 4 cats replaced. Mechanic said one bank was completely disentegrated and the 2nd bank looked fine. CEL turned on a few days later for o2 sensors but Truck drove well for about a month until it started to not get oil pressure for a few seconds on start up which lasted 1 week. The oil pressure delay increased day by day and truck developed drivetrain noise.

My father had a friend take a look at it to replace the oil pump. Got it back a day later supposedly fixed and finally the truck started spewing some white smoke and smelled like gas and rotting eggs. It also had random misfire, no power and engine sounded rough. My oil level also went down and looks like it was contiminated with water/coolant. Ive suspected possible head gasket.

I got my Taco so I just left my Frontier sit for 1 year with no driving.

Today I decided to look at it and I removed the intake manifold and found what looks like oil or jellied gas around the intake passage opening. The spark plugs looked ok, while one of the coil plugs looked burned.

Current codes are p0300 and p0603

 

sounds like a head gasket. white smoke is usually water vapor, blueish smoke is oil. gap looks a little larger but i'd check that. Check your compression on your pistons, that will tell you if you have a leak--or blown head gasket. How many miles on it?

 

Truck has 119,000 miles. I wonder if the timing wasn't set correctly when the oil pump was replaced.

 

Im not sure how the oil pump is in the nissan engine but unless they cranked the engine when they took it out "normally" it shouldnt mess with timing unless they moved either a camshaft or crankshaft.

 

Unless it was like -70° i dont think that gasoline had jellied. Can you tell if the coolant is low or is there oil in the top of the radiator (the radiator cap not the reservoir) is the oil milky?

 

I've drained and refilled the coolant with water many times in my attempts to fix the engine with a sealer. The oil looks black and watery, and the oil level also went down but the smoke coming out isn't blue to indicate oil burning. I remember I had changed the oil not too long before It started acting up.