NoRotors.com - RX7 Engine Swap Forum

Technical Information => Electronics => Topic started by: rx_evo on January 15, 2015, 01:11:46 AM

Title: RPM problem trying to figure out how to calibrate it correct
Post by: rx_evo on January 15, 2015, 01:11:46 AM

Hey guys I just finished doin the Ls swap it's all doin good running strong am having a problem with the rpm guage it work good and all but it reads wrong do I need to buy something special to calibrate it so it reads correct? If you guys could help me out that would be great thanks
Guys

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: halfspec on January 15, 2015, 08:24:01 AM

Assuming that it's working and you're not using a Gen IV+ LS PCM that's missing it's pullup resistor...

Is it too fast or too slow?

The RX7's tach accepts a signal of 2 pulses / rev. For reference, this is how most modern PCM's output a tach signal based on cylinder count:

V8 = 4 pulses / rev - The exception being LS PCMs which output 2 pulses / rev (good for us)
V6 = 3 pulses / rev.
4banger / rotary = 2 pulses / rev.

If you read my notes above you'll see that stock for stock the LS PCM should match the RX7's tach gauge, however, if you're PCM config has been changed to 4 pulses / rev or something else you'll read too fast or too slow and it will have to be reconfigured / retuned.

Lane

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: rx_evo on January 16, 2015, 03:32:36 PM

Is it going fast let me take a video and post it so u can see thank you for the help

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: halfspec on January 17, 2015, 07:42:50 AM

If it's too fast your pcm pulse / rev count is set too high (3 or 4 pulses / sec) and it needs to be adjusted down go 2 pulses / sec. Tuners do this in hptuners or efi live software suites.

Lane

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: rx_evo on January 17, 2015, 02:40:41 PM

Oh really because am Getting ready to tune the car will the tunner  be able to fix that proble
 

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: halfspec on January 17, 2015, 02:47:59 PM

Quote from: rx_evo on January 17, 2015, 02:40:41 PM

Oh really because am Getting ready to tune the car will the tunner  be able to fix that proble
 

Yes. Any tuner worth their metal should be able to solve this issue in 15 seconds with a LS PCM and HPTuners / EFI Live

Lane

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: awd-rwd racer on February 17, 2015, 05:50:18 PM

so you dont need a digital dakota? you can just adjust the pulse setting in hp tuner and done?

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: halfspec on February 17, 2015, 08:48:35 PM

Quote from: awd-rwd racer on February 17, 2015, 05:50:18 PM

so you dont need a digital dakota? you can just adjust the pulse setting in hp tuner and done?

Yes. DD is only for speedo waveform and frequency correction.

Lane

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: GTR on March 08, 2015, 02:27:46 PM

What about the Holley HP ?

Mine is too high and I'm trying to figure out what to do

Title: Re: RPM problem trying to figure out how to calibrate it correct
Post by: Negrok20r on March 08, 2015, 03:31:41 PM

Quote from: GTR on March 08, 2015, 02:27:46 PM

What about the Holley HP ?

Mine is too high and I'm trying to figure out what to do

To setup a Tachometer output that operates at a different pulse frequency than what is built into the software.

You will have to add the I/O ICF – same steps as adding the Transmission and DBW ICF’s.

From there you will create a PWM output,

After this is created you will go to PWM Setup and set the output up as RPM Based.

However, you will have to do your own math to determine what multiplier and divider you need to use for your tachometer.