I've had my PFC w/ commander in for about 3 months now but I just realized that the RPM on the commander and my tach. were different. At idle and before 2500, the RPM's seem to match up. On the freeway I set my cruise control at 3k - 80mph(accord to my tach). I'm exactly at 3k, I take a look at my commander, and I'm at 2780. I floored it to 8k and my peak RPM hold only showed 7700 or so. So I set my rev limiter on my PFC at 7800 but really is 8100 on my tach. Is there a way to calibrate this? Is there a bad sensor somewhere? Which is true? Thanks for any input guys.

Jeremy

 

It's the stock tach - it has some error to it. Dunno if there's really a way to re-calibrate it to make it more accurate.

Dale

 

I remember reading somewhere that if you have taken your guage cluster apart you have to manually reset the tach. Not sure if this is true or not. I will try and see if I can find the thread.

 

i think they are both gettin the voltage from the same signal right? the most accurate way is to get something that gets the rpm from the igntion wire or coil.

but to answer your question, i'd go with the PFC

 

Not sure if this one will help..

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/resetting-gauge-needles-358031/

 

I had the same problem on my FD. The stock tach would read about 3000 rpm at 80 mph but sometimes it would read close to 4000 under the same conditions. I installed a 5" tach and have not had the problem since. Also after installing the tach I was a full second quicker in the quarter mile because I was shifting at the right points. So it is definitely your stock tach. Hope this helps.

 

The stock tach converts an electrical input signal to voltage to move the sweep hand of the tach... analog. The PFC converts an electrical input signal to a digital readout. The inaccuracy is in the the analog gauge.

 

Dale and Jim, thanks for the info on which is correct and how info is sent to each. I will look at my commander from now on when needing to know RPMs.

Thanks for the tip. I have not taken my gauge cluster apart before.

Thanks everyone for the info.

Jeremy

 

Just go by whatever is lower

 

the commander it is

Jeremy

 

If the tach is wildly off or jumping around, it needs to be re-soldered - the solder joints are broken.

Dale

 

I have had significant problems with my Tach untill !!!! I did the Tach fix courtesty of David Scott
basically over the years the solder behind the tach get humidity leading to problems. I have the PDF file David prepared and can send it to you by email or even better you can ask for it directly from David
In any case, you don't seem to be having a severe problem so I would suggest you trust the reading on the Power Fc