Jump to content
NotJustToast

GP PWN table for tach???

Recommended Posts

So, I just tried to modify my AE86 original tach but removing the 30ohm resistor and using a 10ohm instead as Mark Panic instructed from Panic Wire. The tach works now but is not accurate and does some weird stuff compared to others that have done this same mod. I asked Mark and he said "If the tach is off outside of a certain point it's best to use a gp pwm table instead of "tacho".. You can start with a fixed duty of 60 and build the table by rpm. You should be able to do this without the car running." I have no idea what a gp pwn table is or how to do this. Any suggestions would be most appreciated. Car is using a Link Monsoon G4+ in a 1985 Toyota Corolla.

Share this post


Link to post
Share on other sites

first, what sort of inaccuracy are you seeing? there is a way to calibrate before you try before jumping into alternate PWM tables. This assume tacho movement is linear, but just not correct.

* multiplier - if the tacho needle only moves 800rpm for every 1000rpm of engine speed, set the multiplier to 1.2 (or 0.8 to correct it the other way)

If you have something non-linear in the tacho (correct up to 4k then only moves 500rpm for every 1000rpm or something), then heres how to do generic PWM output instead of a tacho signal.

Set an aux output to GP PWM (aux 1-4 will do up to 500hz, 5-8 only 300hz). Note that 500hz only drives a 4 cyl tacho to about 8k. This is a limitation of the GP PWM tables - a normal tacho output can do higher frequency.

Set the condition to "only cond 1" and something generic like "rpm > 400rpm"

Set PWM frequency to "table"

Set the PWM DC table for this aux to all 50% (axis options dont really matter, ive set it to 2x cells of RPM but not required). This value may need to be tweaked for your car

Set the PWM frequency table to have only 1x axis of RPM

Set the numbers in the PWM frequency table to be the frequency of pulse sent to the tacho at that rpm. [freq = rpm / 60 * number of cylinders .... plus your fixup number]

image.png.7f6366161072b5b30dd39cd16d1d9b73.png

image.png.cd996546ff27621adbdc9abfb702b742.png

image.png.4a0cdce5e99a4726d825ea81cf824c3d.png

Share this post


Link to post
Share on other sites

Thanks for explaining the pwn tables, you really helped me understand how this works. I messed with the tacho duty cycle and multiplier and it seems the tach is pretty close to where it suppose to be  "only checked up to 3k because I couldn't drive it today." Now the weird stuff.....When the tach is first plugged in everything sits at 0 where it is suppose to but the moment I switch the ignition on the needle never goes below 100-200 rpm, and when I turn ignition on "after the sweep" it sits at about 500 rpm. Once the car is running the needle does not move smoothly and has a jitter or hesitation movement when going up or down in rpm. If I quickly blip the throttle to around  2k rpm "on the laptop" my tach only makes it to 1300-1500 rpm. I uplaoded a few pics and a vid of the 2k blip for reference. Thanks again

cluster after turned off.jpg

cluster ign on.jpg

cluster unplugged.jpg

Share this post


Link to post
Share on other sites

what are you currently using as your duty cycle? maybe try adding or removing 10-20% from it and see if that helps. You could also try putting in a 5ohm resistor rather than 10ohm as I seem to recall there was a lot of discussion on the correct value to use with some people even jumpering it with no resistor (but I wouldnt reccomend that). Its been a while since I modded a toyota tach and it was a couple years newer than yours but they certainly *can* function well from a link with just that resistor mod.

Share this post


Link to post
Share on other sites
On 1/15/2020 at 1:41 AM, cj said:

what are you currently using as your duty cycle? maybe try adding or removing 10-20% from it and see if that helps. You could also try putting in a 5ohm resistor rather than 10ohm as I seem to recall there was a lot of discussion on the correct value to use with some people even jumpering it with no resistor (but I wouldnt reccomend that). Its been a while since I modded a toyota tach and it was a couple years newer than yours but they certainly *can* function well from a link with just that resistor mod.

I messed with the duty cycle a bit going as low as 20 and as high as 90 percent but it did not change anything. I went on amazon and ordered some 5ohm and 1ohm 1/4 watt resistors to try and will let you guys know what happens when I get them. Thanks for the help.

Share this post


Link to post
Share on other sites
10 minutes ago, Brad Burnett said:

When i modified my stock tach in my ae86, i didnt even use a resistor.

So did you just remove the original resistor and bridge those 2 points with a wire and it worked fine?

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...