i installed the mileage master ign. upgrade from jacobs and everything worked real sweet for about 4 months. then one morning it started to misfire on cyl. 3 and 4 these 2 share a coil so i unplugged the jacobs and hooked the stock back up no more misfire or engine light.

anyone ever have any problems like this?

 

i doubt this has anything to do with it...but i heard that jacobs is not great quality....but maybe it's just me...anyways....could it be timing?