View Full Version : Speed hut tachometer not reading correct RPM
I am now noticing my tach is about 300 RPMs off. Car has been on the road 4 years now and up until recently (last month) it has been fine. I took the gauge bezel/glass off the front and re-aligned the indicator to zero but it still is showing 300 RPMs off when the vehicle is running. I was going to give speed hut a call Monday but thought I would see if anyone else has an idea of what might be causing this? recommendations to get it back to reading properly? Engine is SBF dart 427, Pro Flo 4 EFI w/MSD box.
Thanks, Travis
MB750
06-15-2025, 07:08 AM
I had a similar problem a few months ago after I did some grinding to my DIY carbon fiber dash. Turns out the front ring loosened up during the vibrations and made the dial (the thing with the numbers on it) turn a bit. If zero RPM is actually zero on the gauge, and your calibration is accurate, than it might be an internal issue.
Have you tried a calibration again? For what it's worth, wonky stuff wouldn't be the first time I've heard of this on a Speed Hut gauge. A few months ago my speedo all of a sudden jumped around 45 mph fast. It was like it just forgot where zero was. A restart fixed it.
I had a similar problem a few months ago after I did some grinding to my DIY carbon fiber dash. Turns out the front ring loosened up during the vibrations and made the dial (the thing with the numbers on it) turn a bit. If zero RPM is actually zero on the gauge, and your calibration is accurate, than it might be an internal issue.
Have you tried a calibration again? For what it's worth, wonky stuff wouldn't be the first time I've heard of this on a Speed Hut gauge. A few months ago my speedo all of a sudden jumped around 45 mph fast. It was like it just forgot where zero was. A restart fixed it.
Was not even aware you can calibrate the tach, I will check into this.
AtlantaCobra
06-16-2025, 08:38 AM
I'm having the same issues. How do you recalibrate the tach? I've noticed the speedo getting off sometimes as well. It seems to eventually fix itself, but my tach is consistently off.
PNWTim
06-16-2025, 09:13 AM
You should have the little button that plugs into the tach. It allows you to cycle through the pulse count coming from your engine so you can program your tach to match your engine type.
MB750
06-16-2025, 07:03 PM
Yea, the instructions that came with the Speed Hut gauges shows the calibration procedure. You might be able to download it, or ask their Customer Service for a copy.
Basically you plug in that button into the back of the tach, then hold the button down and turn the key on. That initiates the calibration procedure. Then you press the button so the needle sweeps up to a certain number of pulses per rev, then hold it down to lock it in.
Or something like that. ;)
MB750
06-16-2025, 07:07 PM
Here you go:
https://store-ta980ko58k.mybigcommerce.com/content/instructions/4in%20to%204.5in%20Tachometer%20Shiftlight%20LED%2 0Instructions.pdf
Only on ours, the menu button is a small harness with a headphone jack on one end and a button on the other, it's about a foot long. The jack is in the back of the tach.
AtlantaCobra
06-30-2025, 08:00 AM
Hey guys. I did the recalibration but my tach is reading about 500 rpm too high. I've noticed when turned off, it resides at about 500 rpm. Any way to manually adjust the gauge to the proper reading?
rich grsc
06-30-2025, 11:56 AM
Why aren't you asking Speed Hut?
Jeff Kleiner
06-30-2025, 12:06 PM
...I've noticed when turned off, it resides at about 500 rpm...
That's normal. When you shut off the ignition it kills power to the gauge and the needle just hangs. Turn the ignition on but don't start the car and you should see it go to zero.
Jeff
AtlantaCobra
07-01-2025, 01:11 PM
Why aren't you asking Speed Hut?
Good suggestion....smartass
AtlantaCobra
07-01-2025, 01:13 PM
That's normal. When you shut off the ignition it kills power to the gauge and the needle just hangs. Turn the ignition on but don't start the car and you should see it go to zero.
Jeff
Yeah I've done that and it still stays at about 500rpm. I'll see if I can pull the gauge and access from behind somehow. Or maybe I'll call speed hut :)
MB750
07-03-2025, 06:13 PM
Yeah I've done that and it still stays at about 500rpm. I'll see if I can pull the gauge and access from behind somehow. Or maybe I'll call speed hut :)
With the key on but the engine not running, it should say zero rpm.
If it's idling when you turn off the key (which is normal) the tach will read the last RPM before it loses power.
If you turn your key on (but NOT the engine) and it's not zero, you need to clock the dial. Unfortunately that's not in any manuals I've seen, but it's not hard. Take the tach out of the dash, remove the front bezel and glass, lightly turn the dial so zero = zero, then delicately put everything back together so zero stays at zero.
AtlantaCobra
07-07-2025, 09:41 AM
With the key on but the engine not running, it should say zero rpm.
If it's idling when you turn off the key (which is normal) the tach will read the last RPM before it loses power.
If you turn your key on (but NOT the engine) and it's not zero, you need to clock the dial. Unfortunately that's not in any manuals I've seen, but it's not hard. Take the tach out of the dash, remove the front bezel and glass, lightly turn the dial so zero = zero, then delicately put everything back together so zero stays at zero.
Thanks for the suggestion. I'm going to give this a try. One thing that might be causing this to happen is that I usually kill all power from the battery after each outing. Your comment about the "tach reading the last RPM before it loses power" made me think of that.