What wire makes the tach work? 1994 OBS Z-71

[Z-Rod]

Hey guys,

I hooked up my tach wire from the 2005 PCM to the white coil wire from the existing harness. I have not had any luck getting the tach to work. Yesterday, I tried the "pull up resistor" and still no change. There doesn't seem to be much advice out there and it makes me think you guys never had a problem. My computer was been tuned, so I am certain it is my wiring and not the PCM.

Any ideas?


Z-Rod

[el guapo2]

http://lt1swap.com/lsx_tach.htm

[Z-Rod]

OK-

I realized that the first resistor I tried had different colored bands and was not the required 680 ohm resistor needed. I picked up the correct 680 ohm resistor and will wire it up this afternoon and hope it works. If it does- Awesome!!!!

If not... plan B, anyone.........



......... anyone............. anyone..........


Z-Rod Out

[Z-Rod]

It works,

After wiring in the correct resistor my tach is alive, thanks for helping with this... The tach is my favorite gauge and is the only one that didn't work from the start. I found out from Radio Hack that some stores carry a full version of resistors and other stores carry about 1/2 of the resistors. I bought a pack of 5... and this is reason enough for me to plan on at least 4 more conversions. I would love to put a LS engine in a 1964 Buick Riviera. The 1964 GTO is often called the first "real" muscle car and I agree. But the 1964 Buick Riviera is a really cool looking car with very clean lines. Look it up and see if you don't agree that putting a LS engine in that car would be totally awesome. Of course, there is nothing I would rather drive more than my OBS Z-71 with a 6 liter Super Sport package... SWEEET. But if I am going to have a collection of 5 LS conversion cars... that Riv would be on my list.

Anyway, thanks to everyone that helps make this site great !!!

Z-Rod

[LS1GMCTruck]

Z-Rod...are you using the factory tach, or an aftermarket tach? Is the resistor needed for factory tach use? thanks

[Z-Rod]

I am using the factory tach. There is a white wire coming from the new computer that is the tach signal. The 680 ohm resistor is needed to make the PCM's signal work with the OBS tach. Without the resistor, my tach never moved. All of my gauges work perfect now, next is the cruise connections. I have the diagram, I just need to run the wires from under the dash to the PCM pigtail, right after I get that pigtail from the salvage yard. After that, I will finish the 4wd wiring. I need to send the PCM a signal when I am in 4wd low so it will change the shift strategy.

So far I have not encountered any surprises from the swap that were not caused by me... I think I hooked up my fuel filter/regulator bassakwards... oh well.

Z-Rod Out

[BlownChevy06]

hey can you explain how do we wire this 680 ohm resistor to the PCM tach signal wire and excicting white wire...? do i "T" it in between both wires with +12v switch?

[haveTBIwantLS2]

GOod job on fixing the prob.
I thought I was gonna need to do this since my truck is a 91, but the tach came alive when I fired my rig up. weird