at 2500 does it stay rough from then on as high as you rev it? is that part or WOT or cruise. I would measure the vac & fuel psi & timing at that exact point when it starts to act up. Yes do a compression test & maybe a leakdown & try the new plug first & see if the new plug straightens it out for awhile. Describe the roughness (shakeing/missing). EDIT if it dont continue to be rough from 2500 on up, how much more RPM does it continue to run rough?
It’s hard to describe the rough spot, I just know it happens in every gear at the same rpm.
Starts around 2500 and continues on up as far as I can tell.
It almost feels like a driveshaft vibration and sounds like one in the cab specially when I get the rpms up higher around 3500-4000 rpm.
Seems like it takes a little longer to cycle once im at a higher rpm around 3500-4000 rpm if that makes sense.
At 2500-3000 it seems like its cycling pretty quick and the higher the rpm goes up the slower it gets but it’s still there.
You can feel it in the floor boards in the steering wheel, in the seat.
I know this isn’t a drivetrain issue becuause it’s rpm dependent not speed dependent.
I have a 1350 series cv shaft for a rear driveshaft, pinion angle is set perfectly at -2 to -3 so that the pinion is inline with the shaft while driving.
For the longest time I thought this was drivetrain related but now I’m convinced it’s not.
My converter is correct I’ve verified that, flex plate is correct.
Balancer is correct.
And like I said since it’s rpm dependent the drivetrain theory kind of goes out the window.
I’m convinced it’s in the engine somewhere, ether ignition or there is an issue with one of the cylinders.
Its just strange cause the last time I did a compression test all cylinders were dead even at 150 psi.
Below is a pic of the spark plug that came from cylinder 8.
The plug on the left cane from cylinder 6 plug on the right is cylinder 8.
All the other plugs looked just like cylinder 6’s plug.
Cylinder 8 was the only one that didn’t look right and smelled like fuel a little bit.
I’m heading out right now to pull cylinder 8’s plug and do a compression test.
The engine is still warm from driving it home from work.
I’ll report back with what it puts out, last time it was 150 and that was only like 6-8 thousand miles ago and I never abuse this engine.
I baby it big time.
So I don’t see how compression could have just dropped in one cylinder all a sudden.