at first i thought the vibration wasnt the engine, but i had the driveshaft, tires balanced and got 2 new u-joints. now, im pretty sure its the engine. it vibrates in park, but does it worse driving down the road, and when you let off the gas, its fine. only vibrates during acceleration. the engine is totally new, only 4000 miles. it started doing this about a month ago, but i had been doing all of the balancing to fix it.
the number 8 spark plug keeps fouling. i know it is getting spark because i changed the plug and left it out to see if it was sparking. it takes probably 50 miles before it wont fire any more. i changed the plug and some vibration went away, but probably 80% of the vibration is still there. i pulled all the plugs checked the gap, still vibrating. brand new wires and plugs, maybe 50 miles on them, the cap and rotor is new with the engine(4000 miles). i have a msd-6a also. the only work that i have done to the engine is the ignition. nothing else has changed since the engine was bolted in. i am using bosch platinums(not +4's), msd super conductor wires. someone said maybe i should try ac delcos? thanks for reading this.

 

Run AC Delcos!!! Those Bosch are junk! As for your vibration problem all I can say is check the ballancer to make sure its the right on and on correctly. I am not sure but maybe the Tq converter or the flywheel may have come a lil loose? I would ask about the flywheel but it would make sence.

Hope I helped a lil bit

-Terry-

 

i just changed to ac delcos and put on a new cap and rotor and everything is still the same. i will check the flywheel and tq converotr tonight. thanks

 

is there a way of telling if the damper is bad? cause my 383 is externally balanced, and if the damper went bad there would be a bad vibration. the damper is new though, 4000 miles as the rest of the engine.

 

Since the vibration could be related to the misfire and fouling plug, I'd suggest a compression or leakage test on the suspect cylinder. Something is very wrong there if a plug won't last more than 50 miles.