I had a random miss fire on cylinders 5 & 6

I just replaced the coil for cylinders 5 & 6. I could not figure out why I had a random miss fire that would happen every 15 to 20 seconds. All the spark plugs were new last year with less than 500 miles and the color looked good on all plugs. I rebuilt the carburetors last year, replaced the timing belts and used my Digi Sync and all was good.

I ended up using a Gunson Color Tune and found out that the flame was very low in cylinders 5 & 6. The other 4 cylinders had a bright blue flame.

I purchased a used set of coils & plug wires (didn't know if the wires or coil could be bad) and I swapped out the coil for cylinders 5 & 6. Now I have a bright blue flame in all cylinders. I rechecked with the Digi Sync and had to do a very minor adjustment. I also tested for a vacuum leak using propane and no leaks.

Everything is running normal and no miss fire. Now with engines hitting 20 years old problems are starting to appear. This may help someone with the same problem.