Oldsmobile/Buick Repair: Buick 3300 V6 Misfire Shake, buick century, gm parts

Question
Hi Van; I have a 1989 Buick Century with a 3300 V6 engine.I have what I think is a severe miss. When I do say 60 mph and try to maintain that speed the car starts shaking severely so I apply throttle using a feather action or let off the throttle slightly and it stops shaking.To drive on the hiway I have to throttle on/ throttle off to stop the car from shaking me to death. it has a 3 coil setup and I have changed the middle coil twice as there was none or very little spark from the #2 coil wire when unpluged from the coil. Could the computer be telling the coil not to send a spark? all the other 5 coil terminals send a very definate spark and I have tried 2 brand new coil modules as well as switching them around with no change to the cylinder #2 spark

Answer
Hello Harry,
Sounds like exactly what mine sounded like.
Shakes especially in overdrive, but if you floor it, will temporarily quit?

I don't think the spark is the problem.
Do a compression check, but watch the needle closely. You may even want to do each cylinder several times, because mine all got up to about the same pressure, but I happened to notice that one of them seemed a little different in the way each stroke hit. One cylinder wouldn't be quite as stable, or even, if you want to call it that.
Like a valve sticking.

Turned out to be a broken valve spring. Two springs on each valve...an inner and an outer.

By using compressed air, you can remove and replace the springs without removing the head.

GM Parts man said he actually sells quite a few singles like that.

Really not all that hard a job.

Of course, yours may not be that, but it does sound familiar.

On those double coils, both wires fire at the same time, so if they will reach, you can swap them, to see if the miss moves with the wire, or stays with the cylinder.

Van