Tach is too fast on LS1 NB swap
 

One of the little things that I have still yet to work out on my car, is the tach speed. I went the FM route and wired in a hot wire with a 2.2k resistor to jump up the signal, but the gauge shows high all the time. I have seen where some people did not wire in the extra hot, any tips?

How far off is it? Maybe try taking the resistor out?

I had a Glowshift gauge and used this....Tachometer Filter

I would say its around a 1000-1500 too high, I have not actually put a monitor on it to see. If I remove the resistor, won't that make it go up? More voltage=Higher signal? I was thinking that on nathans site, he said just hook the wire up, wondering if it is not actually needed.

I just started up my 2000 base model project and I'm having the same problem. I'll let you know if I come up with a fix. It should be back from the dyno shop tomorrow so maybe this weekend I'll have some time to look at it.

Good Luck

Cool bud, thanks

I'm running a 2002 LS1 using the ECM feed to a NB dash from a 99 with with no resistor and the tach seems right to me. It matches both my HP Tuners and Ultragauge anyway.

LOL though I have had some of our Miata brethren say it can't possible be right it's way too low!
https://www.v8miata.net/attachment.p...ine=1458742751

Thats what I am wondering about, it seems to me like by me adding voltage to it has made it too high.

Yeah but wouldn't the resistor cut the voltage?

It would cut the voltage coming in from the 12v source, but it won't affect the signal that is coming from the PCM. The idea is to add an additional constant amount of voltage to the tach signal via the resisted 12v wire. The way they are saying it is below:

Tach Signal=PCM Signal(Voltage Carried)+constant voltage from other source

Ahh I see! So if the reference voltage is lower the tach signal is based on the wrong bench mark so it's off. Well it's a simple test to find out!

Was this ever resolved? Did the FM route and wired in a hot wire with a 2.2k resistor work? I have a 2002 miata and an LS1 from a 2000 Trans Am. Thanks

I bought the resistor from Flyin Miata and installed it per their instructions.
It appears to work accurately.

Hi,

Don't forget that the Dakota Digital universal tacho interface will do any engine to tacho combination. It works a treat :)

So I wanted to update this thread for others benefit in the future. Figured out several of the things that are being discussed in this thread. First of all, 2000 and older PCM's are different than 01/02 from an F-body. As jim mentioned, he runs a 99 PCM without issue. My car has a 2002 PCM and as Grip mentioned above, I was able to go in and modify the tach output signal with the HP tuners software I bought. I tried a bunch of other combinations and resistors and such. This was the only way I was able to figure out to make it work. There is a thread on the HP tuners forum that explains some linked here. Same idea as what Grip linked above, except with the older PCM. With it I was able to successfully line my tach out.

https://forum.hptuners.com/showthrea...der-tachometer

Stng, so you got your tach working by adjusting the low/high res settings in HP tuners on a P59/Gen3 PCM?

I have a 2000+ gauge cluster with a P59 and I also have been tuning it with HP tuners but haven't played with these settings yet and just dealt with it being off.

What numbers did you end up using to get the output accurate?

My PCM is the 411 from a 2002 Camaro. I just had to do a basic signal adjustment, I'd have to look but I think it was the 6cyl setting was right for mine. It was real easy to change and test, and change and test.