I just bought an HEI spark tester and found step by step instructions on how to diagnose. Everything I have seen so far leads me to the distributor but I don't want to run out and have my son get one till I am reasonably sure that is what the problem is. I was just confused because I did see spark when I used a plug in the end of the wire. The instructions I read say that this HEI tester will require a stronger spark to make the arc and I will immediately see a no spark situation. I just never knew a coil would get weak. I thought they either worked or didn't work with no middle ground.