I thought I was safe with the "MSD Heat Digital HEI Module", but it appears not. I had it installed since I got the car back on the road after my father had it parked for almost 20yrs. The car has a converted GM HEI dist on it and for Xmas I had the "Heat Module" on my wish list. Why not have an easily programmable rev limiter (from the drivers seat) along with any other benefits it may add? Upon initial running of the car all was good, then about 2-3 weeks ago I installed the switch needed to allow the programming of the limiter. Seems shortly after that the motor developed what felt like a high speed miss(above 3K rpm). It slowly became worse, any time above 3K the "misfire" was there, steady state or trying to accelerate.
I cleaned both carbs(44 IDF's), TWICE. Still no joy. This morning I went and bought a new coil (as it still had the original 30ish yr old coil in it), still no joy. Then I was searching the web to see how to set the limiter back to default(is the limited instructions don't tell you that part, when I found a forum posting of someone who wanted the add this sort of limiter to his GM car and he used one of these units. Not until he got the wiring hooked up for the limiter, he experienced the same sort of "misfire" I had. He sent it back to the distributor he bought it from and when they sent it back to him, he put it back into the car and had the same issue. Upon dropping the stock module back in, the car ran perfectly(as did mine).
I had an MSD box in my Rabbit for over 20yrs with no issues, and this sort of "progress" is not what I was expecting. I hope this is not how the Mallory line will go...
And his issues were 3yrs ago (I just went back to look at how old his post was).http://www.corvetteforum.com/forums/c3- ... miter.html
I called them today and I am sending it back for "warranty"repair or replacement. Whatever I get back, I won't be using the limiter function nor the "limiter verification" feature. As it was working well before I put those in use. It certainly provides a better signal to the tach, as now it'll jump around quite a bit, not sure if it is something to do with the actual tach(a VDO unit) or the output of the coil/module.