hey i just installed my msd 6a box and now when i go above about 4k rpm the tach starts jumping from about 4k to 2k to 5k to 4k and all over the place. once i drop below 4k rpm the tach returns to normal. i hooked it up right and all the connections are good. i dont know what is making it do this. has anyone else had this problem. the car runs fine even after 4k rpm the only problem is that the tach jumps around thats it. thanks -Matt

 

What I had to do on my 91 Firebird was take the tach output connection on the MSD box and splice it into the wire running from the distributor to the tach. Easiest way to do that is disconnect the white wire single connector next to the distributor and then splice the new wire you run from the MSD into it. Make sure you get on the "tach side" of the connector to splice into. Works fine now.

 

thats how i have it hooked up. i even clipped off the connector and spliced it into the msd wire for the tach, so i can disconnect it if i want to. the only thing i can think of is that i have a bad connection. but i checked all of that.

 

Do you have a tach filter on your 92? My 91 Formula didn't have one, but your symptoms match those of folks' that had one. From what I've heard it's pretty random who got one and who didn't. Look for a small block box, 1.5" or so square, on the firewall with the tach wire from the distributor going to it. If you have one, disconnect it and connect the 2 wires going into it to each other instead of the filter.

 

ok i will check it out when i get a chance today and let you know. thanks

 

Did you cross the wires going to the coil? Sounds like you've got your spark coil wired backwards (instead of + to +, you did + to - )...

 

no i hooked it up as the colors said to. it runs just fine. and i also looked for that black box (the tach filter) and i couldnt find it. i dunno what the deal is.

 

why would having my wires crossed on my coil make my tach jump around without causing the coil to miss and jump around too?