Installed new coil pack and now tach doesnt work.

[GNVAIR]

I was trouble shooting one of my cars the other night and had installed the coil pack and module from my GN onto it. The tach worked fine. I then bought a replacemnt coil pack and module from Advance Auto parts and now the tach doesnt work when the engine is running.However, it does work when the engine is cranking. As soon as it fires, it drops to the bottom. I have checked connections, but so far, I am at a loss..........short of trying my coil pack on there again. Anyone have any ideas what it could be?

 

[KendallF]

I have seen this with some replacement modules..they will function fine otherwise but the signal level to the tach is weak enough to not function correctly. Your only fix may be to replace the module. You might call John Spina at Casper's and see if he has some more intelligent advice.

 

[blackbuick87]

exchange the module for a different one
I have an Advance auto module and my tach works fine

 

[GNVAIR]

Looks like I will be heading back to get another one today.
I will try that. Thanks guys!

 

[GNVAIR]

UPDATE!!

I went home last night and tried the coil pack and module from my GN on the Monte and the tach started work. So, the prognosis is the circuit that drives the tach in the module is bad. I ended up taking both the coil pack and module back and ordering new AC Delco units. No more after market coils or modules for me.