Factory tach not working with lq4
 

I’ve done some searching and read threads but there seems to be some inconsistent advice. My tach worked with hei ignition on my small block. This is a 71 c20 with factory tach. I installed a 6.0 lq4 and had the harness reworked by current performance. I connected the “tach” wire to the tach where the hei was hooked up. Not getting any reading. Some people say resistor, some people say I need a Dakota converter, others say program to 4 cylinder in hp tuners. Any advice is appreciated. Thanks!

Re: Factory tach not working with lq4
 

I have heard about the 4 cyl setting. I have not tried it yet as my swap is not running yet. I just got my HP Tuners kit recently and am planning on using my factory tach. Mine is reproduction type tach though.

Re: Factory tach not working with lq4
 

You won't need any kind of converter box to make it work if you have tuning software, which is needed to remove VATS anyway. What you need to do is change the tach resolution from 6 to 3 in the tune to change it to 8 cylinder instead of 4cylinder. That will make it read right, but only if it works in the first place. To make it work you will probably need a pull up resistor to strengthen the tach signal to the tach as some PCM's don't put out a strong enough signal to work an older tach. LT1Swap has a good write up on how to do this. https://lt1swap.com/lsx_tach.htm

Re: Factory tach not working with lq4
 

Kinda of a dumb question but did you disconnect any of the other wires from it? There are usually three: power, ground, signal.