Bad bad bad BAD misfire!

[oldsman003]

Hey folks, i have a terrible problem. I own a 2004 Yukon XL 2500 4x4 6.0 200k miles, I purchased the truck in April for a tow vehicle, I have horses. Towed great at first. seemed under powered but figured was normal because i made a transition from a 12 valve Cummins dually to this. But then became obvious that was not the case. started to struggle with 10k pounds behind it, then started struggling with only my empty 3500lb trailer and quickly got bad enough i simply cannot drive it anywhere. all within 3 weeks. Very quick downward spiral.
Now it misses on every cylinder on bank 2

Steps I have taken in the attempt to fix this

I have replaced with new or used but proven working condition parts
-throttle body
-crank sensor
-cam sensor
-map sensor
-vacuum sensor
-PCM
-MAF sensor
-air box (has afe, replaced with stock and back no diff)
-acdelco plugs
-champion wires
-coils
-injectors
-replaced and added larger sized engine grounds
-o2 sensors

A mehanic hooked it up to a tech 2 tuner and could not find the problem, advised me he thought it was a burnt valve, I pulled the passenger side head only to find this engine is a fresh rebuild that still has hone marks in the cylinders, so clean you could eat off of it.

My cats were clogged and at the moment are cut off waiting for replacement after truck gets running right.

I am baffled at this issue and am tired of throwing money at it, and it seems I cannot find anyone who knows anything about anything.

I have tested fuel pressure and compression fuel psi is a solid 61psi at the rails and every cylinder pushes between 110-125psi on my gauge.


HELP PLEASE!!!!!!!!

 

[ezdaar]

Simple questions..

Have you checked drive line for seizing components?
Have you checked for dragging brakes?
Have you checked input vs output shaft speeds on trans to see if its slipping?

Have you checked for full cam lift? Possibly gone flat due to improper build..
Did you check for a vacuum leak on intake manifold?

 

[oldsman003]

Simple questions..

Have you checked drive line for seizing components?
Have you checked for dragging brakes?
Have you checked input vs output shaft speeds on trans to see if its slipping?

Have you checked for full cam lift? Possibly gone flat due to improper build..
Did you check for a vacuum leak on intake manifold?

Intake is good, just had it off to pull the head and all looked great. Not sure of cam and I'm really not entirely certain what any suspension or braking components would have anything to do or any effect on how my engine is running.

 

[Walkercraig01]

Catalytic converter?

 

[oldsman003]

Catalytic converter?

As I stated above they were clogged and are cut off right now awaiting replacement as soon as I get it running right

 

[SLCHOE]

Were those cats on the truck when it wasn't running right? A plugged cat WILL KILL power, cause misfires and limit RPM.

 

[oldsman003]

Yes they were but this misfire started as a slight random miss, and inside of 3 weeks progressively got worse and worse to the point of not being able to be driven. The passenger side cat I'm sure was clogged and causing power issues but by it misfiring and the amount of raw fuel from 4 cylinders completely trashed it. As it sits right now the truck only runs entirely on bank 1 drivers side and completely misses on every cylinder on bank 2 passenger side. I have beat myself up over this and HAVE to get it back on the road asap. She has sat for a month and a half now and between the cash I dished out already for parts and gaskets from removing the head and a mechanics time with a tech 2 for diagnosis which got me absolutely nowhere. I am not sure what else this issue could be. The motor ran great when purchased less than 2500 miles ago. I towed my impala home with it 2.5hrs and have towed my horses around but the underlying issue was a abrupt stair step downward to where I really do not think it can move itself out of the driveway

 

[Marv02]

Like other say look for a flat cam pull the valve covers and see if the rocker arms are moving the full travel.

You said the compression is good all Cylinders.

Is missing at idle through the wide opening throttle.

When Is cold or hot is happens in open or closed loop mode.

Did you do a Radiator pressure bleed down check Antifreeze don't burn.

What color is you're oil.

 

[oldsman003]

oil is normal, coolant is normal still factory dexcool (will be flushed and swapped as soon as truck is road worthy) misfire is apparent cold or hot, does not change with open or closed loop. how would i go upon checking the lobe travel?
i guess my question is it was running fine and inside of 3 weeks went from running fine to runing on 4 cyclinders how could a cam go bad that fast???

 

[Marv02]

Did you check for Vacuum leaks.

And did check for codes if so what codes if any did it give you.

Do a compression check on each cylinder first.
If one cylinder has low compression Pull the valve covers watch the rocker arms compare it to the other see if they have the same range of movement of travel as rest if they don't It could be a flat cam or a collapse lifter.
Next put the cylinder on compression stroke put compressed air in to that cylinder and if it starts leaking at if comes out the intake you have a bad valve, valve seat or a valve hanging open, If comes out the Exhaust same for the exhaust the head need to come off.
If the Air leaks out though block as the oil drain going from the head back in to the engine it rings.
Due this to each cylinder one at a time.

oil is normal, coolant is normal still factory dexcool (will be flushed and swapped as soon as truck is road worthy) misfire is apparent cold or hot, does not change with open or closed loop. how would i go upon checking the lobe travel?
i guess my question is it was running fine and inside of 3 weeks went from running fine to runing on 4 cyclinders how could a cam go bad that fast???