Calibrating the TACH for V8 HOW TO?

[Jdperk-86elco]

Hey Guy,

I just got my new EFI and I am playing with it on my swap. My Tach is off but it isn't reading half scale as I was told. I read the PCM and its value is 6.0 but it is unitless so what should I change it to for my stock V8 tach to read correctly. I searched for this answer but either it is simple and I am missing it or no one has asked this question.

[Black02SS]

What kind of vehicle is this for?

[Jdperk-86elco]

What kind of vehicle is this for?


1986 El Camino with 2000 LS1 and 4l60e transmission. I need to set the tach to read correctly so what numbers do I use to change the PCM output to sent a V8 signal to the TAC?

[eboggs_jkvl]

You might need something like this to make that work.


http://www.hawksthirdgenparts.com/inc/sdetail/19294


Elmer

[Jdperk-86elco]

This is EFILive forum guys and there is a TACH adjustment section in the software using a formula. So what I am asking is what should the value I need to set for the PCM to put out a 8 cyclinder signal?

[GMPX]

Not knowing exactly what the El Camino tach is needing, the best way is to log RPM via the scantool, and change the Tach pulses until both the logged RPM from the PCM and tacho match. The RPM reported by the scantool will be correct, the Tach parameters will not change that.

Cheers,
Ross

[Jdperk-86elco]

Let me ask the question another way, the stock tachometer in my cars dash is for a 8 cyclinder engine and the LS1 PCM puts out a 4 cyclinder signal which will make the stock tach read incorrectly. There is a tach setting in EFI that allows the PCM output to be changed.

NOW my question, what numerical value do I enter into EFILive to change the tach signal output of the PCM from a 4 cyclinder signal to a 8 cyclinder signal?

[GMPX]

O.K, but in your first post you said "My Tach is off but it isn't reading half scale as I was told" , I read that as saying it is idling at 600 RPM but the tacho is showing 500.

Anyway, you need to enter 12 into both parameters (G1204 & G1205).
With a value of 6 (stock) it takes two 24x ref pulses to transition the Tach ouput high to low or low to high. You need to make it happen on every reference pulse so set it to 12 as per the examples in the software.

For 2 pulses, use N= 6 < Stock
For 1 pulse, use N=12

Hope that helps :)

Cheers,
Ross

[Jdperk-86elco]

O.K, but in your first post you said "My Tach is off but it isn't reading half scale as I was told" , I read that as saying it is idling at 600 RPM but the tacho is showing 500.

Anyway, you need to enter 12 into both parameters (G1204 & G1205).
With a value of 6 (stock) it takes two 24x ref pulses to transition the Tach ouput high to low or low to high. You need to make it happen on every reference pulse so set it to 12 as per the examples in the software.

For 2 pulses, use N= 6 < Stock
For 1 pulse, use N=12

Hope that helps :)

Cheers,
Ross


That is the information I have been looking for. The current setting is 6 in both places so now I know it is stock 4 cyclinder output and 12 will output a 8 cyclinder output. I noticed there is also a setting to set the tach output high, I guess I need to determine if my tach needs to be high. It is working now so I guess it probably is correct.

If I now set the value to 12 and my tach still reads off compared to the EFI value then I will adjust the value till it reads as acurately as possible. This would be with an assumption my old stock tach is just off to begin with and the adjustment would be to compensate for the tach error.

Thanks Ross that helps a lot.

James

[Jdperk-86elco]

The original setting was 6. I had to change this setting to 4 to get my tach to read correctly or I mean match what EFI stated my RPMs were reading.

Just for everyones info....