I have an 89 IROC originally LO3 305 TBI. I have swapped in an 03 6.0 LQ9. I have my stock tach connected to PCM C2 (green) pin 10 (white); it�s labeled as Engine Speed Signal. But I�m not getting anything on my tach. It will jump when I turn the key on but nothing after that. The tach was working before so I don�t think that it's bad. I have done a lot of research and searching and this is how I understood that it needed to be connected. Am I missing something?
Thanks,
Ryan

 

What Harness are you using..

 

The 03 and up truck PCM's have a different tach signal output and a lot of factory tachs won't work directly from it. If you add a 5000 ohm pull up resistor between a 12 volt ignition line and the tach signal wire, you tach should come right to life.

 

Great, thanks John. That's what I was hoping, but I was scared to try it without some input.

the_merv, It's the factory harness.

Thanks for the quick help.
Ryan

 

HOLY CRAP, this guy's good!

 

Look what he does..

 

yes i know, that is why HE did my harness and pcm for the formula

 

Is the same true on a 02 corvette PCM? Its drive by wire and im having the same problem. Thanks

 

Yes it's the same. You can either add the resistor or you can also activate it in the tune.

 

John, what do you activate in the tune? I've got the same issue ('01 pcm and harness/ 91 Z28 guage) and I'm heading to the local dyno tune shop on Sunday. This is one of the issues I wanted to address.

Thanks

 

You can enable tach pull-up in LS1 Edit in the engine test parameters section. If that's not in your software editor, you would need to go the resistor route.