I will start by saying i am new to the gm/ls world. I picked up a 04 Tahoe with the LM7 5.3 vin T 164k miles. It seems to be having some very common 5.3 issues but I still haven't found a clear path to take it with.

1. Upon start-up, after idling a few minutes it will throw a cylinder 8 misfire code. Sometimes it will be a random misfire code also. Most of the time it pops on right after idling.
2. I replaced the coils, plug wires, and plugs. The plugs that came out looked burnt pink. New Plugs, wires, and coils did not fix the mis.
3. Bank 1 (driver-side bank) spark plug wells are wet with oil. So much so that I can see it coming out and leaking down from underneath. they are damp with oil ill say and not dripping but still an issue. Bank 2 passenger side does not have wet wells.
4. If the truck sits for more than 4 hours I will get a good solid oil burn cloud at start-up. and it definitely uses oil.

My question is where do I start? Do i need to rip it down redo the PCV valve for the oil issue? Do i need new valve covers and intake manifold gaskets? It seems like all these are common problems, but i did not want to run down a black hole of chasing all these issues until i speak with the group and derive the best path to take. The truck is a great daily for me but id like it to run well while i drive it every day. The photos attached are one of the old plugs, two images from underneath the truck looking up under the manifold to the oil wet plug wells bank 1, and two pictures of a new plug after a week of driving. thanks in advance

 

I would do a compression check on all 8 cylinders.

 

1. The plugs look like the mixture is EXTREMELY lean. Might want to check into what tune it has. Might also just need O2 sensors. Datalogging will tell.
2. See #1.
3. Looks like it needs a valve cover gasket on that side. I see no trace or evidence of oil inside the cyl on the plugs, only on the outside.
4. Might want to check VERY CAREFULLY to see if you have the Castech head crack failure. That lets coolant into the oil, which does all sorts of awful things. You'll know instantly when you pop off the leaking valve cover.

Not sure about "rip it down redo the PCV valve for the oil issue". Never heard of that one.

The rusted out thing by the headpipe is a heat shield that protects the motor mount. NBD.

Intake gaskets cannot leak oil or coolant. They don't seal either of those things. The only thing they can leak is vacuum. Probably not part of the issue at hand. Might need new ones, nothing about what you say or show us says it's "perfect" or any such thing, but it isn't the cause of any of your complaints. I'd suggest leaving those alone for the time being. Of course if you have the Castech problem, you'll be replacing them anyway.

 

If the smoke clears after driving, then returns after sitting, that is a sign of bad valve stem seals and or worn valve guides.

 

Check fuel pressure too, cylinder 8 is furthest from the feed line.

 

Are we for real not gonna mention the #1 cause for truck misfires and potentially a lean condition???


INTAKE MANIFOLD GASKETS

 

Not really common on a well maintained engine.

 

It's super common, especially if the "flex fuel rated" gaskets were ever used

look up "cold start misfire LS" 9/10 times it was intake gaskets


I'm also curious to know how changing your air filter and oil on time is supposed to keep the intake gaskets from wearing out. What other maintenance could you possibly do to keep those alive?

 

this was one of my thoughts as well.

The smoke does not continue after i fire the truck up. it only occurs once the truck has been sitting for more than a few hours

I heard the PCV valve could be clogged which could cause the smoke condition. There is no tune on the truck i purchased it from and elderly gentleman. Ill have to look into the Castech head failure and read about that. That wasnt something that popped up in my initial search.

I am also starting to wonder if it might be worth it to take a shot on another lm7 and just swap motors. I found one for $500. Just dont want to run down a rabit hole of chasing issues when it may be cheaper to take a chance on another motor.

 

I believe the intake manifold gaskets leak on cold start-up when the gasket material is shrunk a bit. As the engine warms up the gasket expands and can seal up the leak.

Since you changed plugs, wires and coils, then look for what could be causing the lean condition. Do you have a scan tool that has live data? If you monitor fuel trims while revving the engine, you can almost certainly make the right call if vacuum leak or not.


PCV valve is easy to get to and inexpensive. Worth a try to simply replace it.

Would an oil analysis determine if engine is burning oil such worn piston rings? Need to determine if it is (or something else) before embarking on swapping engine.