Replacement motor questions but hopefully fixable

[rockdogz]

So I swapped injectors with cylinder 2 and the P0304 came back - cylinder 4 misfire. I also pulled the valve cover and all rockers are moving up and down. Not sure where to go from here.

 

[Rocket Man]

So I swapped injectors with cylinder 2 and the P0304 came back - cylinder 4 misfire. I also pulled the valve cover and all rockers are moving up and down. Not sure where to go from here.

Is the harness swappable?

 

[rockdogz]

Is the harness swappable?

I think so, I will try.
If it was a cracked head then would the cylinder hold compression?

 

[rockdogz]

I can swap the coil harness but not the injector harness

 

[Rocket Man]

I think so, I will try.
If it was a cracked head then would the cylinder hold compression?

Pretty sure it would depending on where it’s cracked.

 

[rockdogz]

Swapped the coil harnesses and misfire on cylinder 4 still. It sounds like a lifter based on a YouTube video I saw where they had a bad lifter. Just not sure why the rockers are still moving then.

 

[wsteele]

Swapped the coil harnesses and misfire on cylinder 4 still. It sounds like a lifter based on a YouTube video I saw where they had a bad lifter. Just not sure why the rockers are still moving then.

Exhaust leaks can sound like a lifter tapping. Not the cause of your misfire if it is, but it could be where the sound is coming from. You might check to make sure all your exhaust manifold fasteners are still there and check closely for exhaust leaks.

 

[89Suburban]

Did you pul

Swapped the coil harnesses and misfire on cylinder 4 still. It sounds like a lifter based on a YouTube video I saw where they had a bad lifter. Just not sure why the rockers are still moving then.

l the spark plug? Just curious, missed a lot in this thread.

 

[rockdogz]

Did you pul

l the spark plug? Just curious, missed a lot in this thread.

Yes I was due for a a tune up anyway and have new plugs, wires, coils. The cylinder held compression and the rocker arms move when engine cranks and are not loose. Tried swapping injectors and misfire always on 4.

 

[wsteele]

So you have fire (spark), compression (compression tested good) and you have fuel (jury still out on the injector harness), so theoretically you shouldn't have a misfire.

The injectors make a distinct clicking sound when firing. Take a stethoscope (or long screwdriver you can get your ear on the end) and put it on a few injectors while the engine is running. You will hear the clicking as they fire, then move to the #4 and make sure it also gives you the clicking sound. If it doesn't then you have a wire connector/harness issue. If it does, then you know you are getting gas.

With gas, you only have mixture left. That could be a leak in the intake. If you get that far and it isn't the injector harness, try taking some carb cleaner and spray around the intake manifold at #4. If the engine speeds up in idle and smoothes out, you have an intake leak.

EDIT: The intake manifold on these trucks is plastic, so instead of carb cleaner, maybe pick up some of that CRC intake manifold test spray can stuff. Carb cleaner is pretty aggressive stuff, not sure what it might do to the plastic manifold.

That is all I got.