You are nevet going to belive this. I have been having problems with my ignition from the get go. My dis 4 has been having erratic spark above about 3000 rpm and I finally figured it out today. I removed my dis 4 to send it back to msd and was testing my digital 6 to see if it still worked, I thought I fried it but thank god it was ok. I hooked it up to one of the trailing coils to test it. When I spun the crank trigger by hand and could hear a loud pop when it fired. I was so glad that the digital 6 was still working that I didn't think about the loud poping until I happened to look down and see a huge purple spark coming from the outside of the coil and into the mounting bolt. I thought that it was a bad coil so i switched to the other trailing coil and the same thing happened. The only thing I can figure out is that the dielectric properties aren't high enough to contain the spark. Under normal conditions you would never be able to see this so if you are running stock coils with an aftermarket ignition look for this problem. I didn't belive it myself so I caught it on film. They are crappy pics but you get the point. I hope my 3 months of pain and suffering can help someone out.

 

Could it be possible that your coils are arcing and that their insulation is gone? i would get another coil pack and try it out.

 

It did it on both coils. The odds of haveing two bad coils is very low. Also the more I think about it it makes more since. Below 3000 rpm the spark plug still fires even though the coil is still arcing. I think this is because the msd produces mutiple sparks until 3000 rpm so mabe a few sparks still get to the plug. Then when it switches to one massive spark it takes the path of least resistance, trough the coil. Also when you rev the engine the spark would come and go with engine load.

 

That seems to be common with trailing coils.. Especially if they have been run with bad spark plugs...
I have a little test I found by accident that I check all trailing with now, dangle a screw driver blade between the coils towers, with the wires on and engine running if it you see it spark through the casings, the coil is done...

 

Nifty little trick Max, BUT, i would think that if there is a spark arcing between the towers with the cables on, it could also mean that the cables themselves are a little shaddy maybe?

 

Did you say DIS-4 ????

 

or get a mister bottle with water and give the coils a spray. if they are bleeding voltage you will def hear it pop. water also makes it easier to go to ground through the insulation. since creating a high load is hard/impossible at idle

 

Yes I am running a dis 4 on trails and a digital 6 on leads.

 

Thats what I thought initially.. but with bad cable , it tends to leak where the cable is bad or blow right out the spark plug wire boot.. The sscrew drivers just gives a place for the coil to leak to externally visible... On the first occurrence I saw it, and came up with a test, the casing all around the coil exterior had little porous "blow holes" in it, most of the time it was arcing to the body ground underneath the coils where you couldnt see it.. The driver brings it to the surface..
That car just about drove me nuts, the trailing was there, then it wasnt , there then wasnt, but signal was constant..

 

When you had this problem...did it cause the tach to move very jerky? Esp when a hessitation happened?

James