can a coil on a 93 blazer 4.3 cpi have an internal problem and cause constant voltage to go threw tach wire to make a computer think its at 9999 rpms?

 

the white wire on your coil is your tach wire, it goes to pin #4 at the back of yur cluster, check it for connetions, melted or grounding out or whatever.. if the coil had an internal problem your engine wouldn't start or would run like crap for a while & then quit altogether, coils are fairly cheep, $20 at AutoZone, after 18yrs it might could use a new one...if a new coil doesn't work then the cluster is no good and there's no fix for it.....

 

ok thanks i dont have factory tach getting reading threw datastream. the coils sparking properly.