Are you sure it's a 5.9? My 400 Ford $500 pickup was really a 351M as I found out when the 400's pressure plate wouldn't work on the flywheel. Later I discovered that it was a 4" stroke so it really was a 400 by means of a crank and piston swap. So it could be a 5.2 masquerading as a 5.9. That seems pretty unlikely but a lot can change in 20+ years.
It's not the ignition but the real way to find that out is to use a timing light on each spark plug lead and watch the flashes. Even at 3000rpm, a miss in the flash pattern is pretty easy to see. Once you have put the ignition to rest, everything else you said points to a fundamental balance issue.
That means it must be something attached to the crankshaft. Period.
When you wisely ran the engine without the belts and the vibration was still there, it eliminated everything that was not attached to the crankshaft at that moment.
The description of the vibration being worse through a band of rpm is right in line with descriptions of 360s with 318 converters or neutral balance flywheels.
It helps if we stop referring to a 5.9Mag motor as a 360. Magnum engines have enough different parts that even though they share bore and stroke with certain LA engines, they are not LA engines.
It is important to restate that the values for factory imbalance in 360s and 5.9Mags is different. The 5.9Mag uses a smaller amount of imbalance.
IMHO you will be removing the engine and discovering which of the several incorrect combinations you have.
Good Luck!
R.
Im absolutely 110 percent positive it is a 360 magnum.
I still have the receipt from the dealership my dad bought it from as well as the installation instructions.
It's a 300 hp crate 360 magnum purchased in march of 2003.
I don't think I'll need to remove the engine to figure out what's going on, maybe the transmission to see if the flex plate is bent or broken.
I will go around the converter to flex
Plate bolts and make sure they are tight.
The shop that did the transmission wasn't exactly sloppy, they were just over confident not listening to me when I said it's a magnum so the balance is different.
They acted like it was your standard 360 and put that converter on it.
They fixed it without charge once they realized the bad made a mistake.
The timing light on each plug wire is a good idea.
What do I look for in the light strobe to see if one of them is Miss firing.
I was also thinking I could have it put on a scope to watch the ignition events to verify if all 8 cylinders are firing correctly.
Could it be a damaged plug wire that's causing this? Could the ignition coil it's set cause this? It's literally rough feeling at about 2500 rpm, the higher I rev the engine the slower the vibration is to come around.
I know the harmonic balancer on the front of the engine is correct, and I know it's a 5.9 magnum without a doubht.
