What year model do you have. ?
For instance I have a 03 ion coupe 2.2
So I had to buy a tach converter.
I'm using the Dakota Digi s8. Works great simple wire up. If you need any help let me know . The problem I ran in to is my computer in a sum of things changes the voltage reading so say aftermarket tach or sAFC or w.e would only ready half the rpm at any time. Totaly confused me. Then was led to the understanding I needed a tach converter.. I hope this helps bro