e38 Tach output RPMs too high (LS3 swap)

[Benji808]

2013 Camaro LS3/TR6060 swap.

Running tach output from pin 48 with a resistor pickup for the signal. I get signal, but it reads too high. I had high and low resolution set at 6, but it was reading approximately 2x what it should have been. I then read that 6 is for 4 cylinder and 3 is for 8 cylinder so I changed to 3 but now it's approximately 4x what it should be, so maybe I went the wrong direction?

Screenshot attached, any guidance appreciated!

tach.png

[07GTS]

they output usually suit 4cyl standard even tho its an 8cyl, just change the tacho to 4cyl will fix it if u cant change the output to 8cyl, if stock is 6 for 4cyl then try 12 for 8 cyl

[Benji808]

To clarify, you are saying to do one of the following:
1) change to 4 cylinder and run 6/6
Or
2) leave at 8 cylinder and try 12/12

Am I understanding correctly?

Thank you!

[07GTS]

was just thinking if 3 is 4x what it should be then see if 12 suits, i havnt played with that before so just a guess on my part

[pdsq98gt]

Your tach output needs to match the tachometer you are trying to match. What engine did the vehicle originally have? Also gen 3 and gen 4 calibrations had different values for tachometer output. It?s based on the number of teeth on the crank reluctor.

[Benji808]

It?s a Jaguar XJ6, so 6 cylinder. Engine is LS3 gen 4 so I assume 58 teeth.

[pdsq98gt]

I could be wrong. I?m not at a computer to look at a tune. But, your 58 tooth reluctor is actually 60 with two teeth missing. 60 teeth divided by 6 cylinders (60/6) is 10. I think 10 is your magic number for tach output.

[Benji808]

I could be wrong. I?m not at a computer to look at a tune. But, your 58 tooth reluctor is actually 60 with two teeth missing. 60 teeth divided by 6 cylinders (60/6) is 10. I think 10 is your magic number for tach output.

So would that be 10/10 HiRes/LoRes? I found one thread that said 9/10 for 6 cylinder, and the linear math of 12/12 is in a similar ballpark, so sounds like we're getting close.

Do I need to manually change the number of cylinders in the top left of the screenshot, or do I only adjust the resolutions?

Thank you very much!
BR

tach.png

[gtstorey]

How long would it take to try all of the combinations till you get one to work. And you can probably find a pattern and narrow it down pretty quickly,

[Benji808]

How long would it take to try all of the combinations till you get one to work. And you can probably find a pattern and narrow it down pretty quickly,

Sounds like that?s the path forward. Thank you all for the help!