Did you re route the ignition wires exactly like the TSB shows?
Have you replaced #8 ignition wire and spark plug with "known good" substitutes?
Like i wrote in your previous post
looking at all 8 spark traces on an old Sun machine display
could eliminate doubts about ignition.
Those old Sun machines could also do a "cylinder power balance" test at 2500 rpm.
Looking at the valve springs, rocker arms and hyd lifter bleed downs is quite reasonable, as Magnums have been known to have problems in all 3.
A video boroscope makes this inspection quicker and easier but removing valve covers is also worth the time and gasket costs. Looking inside all 8 cylinders with the video boroscope through the spark plug hole is worthwhile. Are there deposits on intake valve stems?
Having down the static compression test on #8 is good. Your 155 is typical.
A "running compression test" also called a dynamic compression test
would also be instructive in spoting a bad valve spring or lifter,
and could even give a hint about intake manifold runner air distribution variation cylinder to cylinder.
Have all the previous worries about the Carb set ups been eliminated?
I removed the valve cover this afternoon and took a close look at both valve springs on cylinder 8 and I’m not seeing anything out of the ordinary compared to the rest of the springs.
I have a leak down tester that I have barrowed from a friend but I haven’t had time to perform the test.
I was told cylinder 8s valves need to be closed while performing the leak down test.
How do I determine when the valves are closed on that cylinder?
The plug gaps are set at .40 cause I am running a crane cams hi-6 cd ignition and a crane cans ps92 e-core coil.
I did another compression test on cylinder 8 while the engine is cold and it revealed 147-148 psi this time.
Is it normal for it to drop a few psi when it’s cold?
I haven’t ran the truck in a few days cause I’ve just been so frustrated with whatever the hell is going on with it.
So you reccomend I call a few shops and find out who has the equiptment to monitor ignition while it’s running and have them bring the throttle to 2500 where the rough spot starts and go from there?
Cause I’m throwing in the towel I have no idea what’s causing this issue.
Number 8s plug looking darker then the rest has me thinking it’s all connected some how.
One thing I can do is turn my chokes fast idle down a little bit more; throw a new plug in cylinder 8 and see what happens.
All plugs are brand new and my plug wires are also brand new.
Coil is brand new, distributor is brand new, timing has been verified with two different lights.
Timing mark on balancer has been verified with piston stop.
This is just strange and I have no idea why this rough spot is a lot more prominent when vacuum advance is connected.
With no vacuum advance it’s much better.