Question:
How do I know if my tach is voltage-driven or current-driven?
Answer:
Typically, a current-driven tach will have a loop of wire on the back where it senses the current. Also, a current-driven tach is normally connected to the plus side of the coil, while a voltage-driven tach is connected to the minus terminal of the coil.
Question:
Can I use TachMatch with a positive-ground vehicle?
Answer:
Yes, you would connect power and ground in the reverse direction - and of course be careful to not touch the circuit board to anything during installation.
Question:
What's a pull-up resistor, and why might I need one?
Answer:
Often, ECUs have "open-collector" outputs. This can be viewed as a switch, with one end connected to ground. If the other side of the switch isn’t connected to anything, it stays at ground potential all the time – on or off. A pull-up resistor connects the other end of the switch to 5 or 12 volts so that when the signal is off, the output will be the 5 or 12 volts, and if the signal is on, it will be ground (0 volts).
Question:
What size pull-up resistor is necessary?
Answer:
TachMatch has a pull-up resistor built into the ECU input. But otherwise, one should use a value that is about 1 KOhm or more. Usually 10 KOhms is a good value. If the value gets too small, it could damage the ECU.
Question:
My tach reads a couple hundred RPM off from your 3,000 RPM test signal, and the potentiometer adjustment doesn’t help. Why not?
Answer:
The potentiometer adjustment is only active for vintage tachs. Standard tachometers operate accurately with the precise, computer-generated multiple of the trigger signal that TachMatch generates. However, you can calibrate standard tachometer output to correct for inaccurate tachometers with the engine-cylinder and tach-cylinder buttons - see the instruction manual for details.
Question:
Can TachMatch be used in other applications?
Answer:
Yes. It can generate frequency ratios from the input trigger signal. Anywhere from 1:8 to 8:1. Clever customers have used it to correct signal frequencies in other applications.
Question:
My tach doesn’t trigger from the TachMatch, why not?
Answer:
TachMatch generates a 12v signal. Some tachs rely on the big inductive “kick” from the coil. For this purpose we designed the V-Boost module. This is usually necessary for VDO tachs used in various makes and models, Jeep tachometers, and many of the Datsun Z-car tachometers.
Question:
If my tach has a different number of cylinders than the engine, and I need the V-boost to make the tach work, do I also need a standard TachMatch?
Answer:
Yes.
Question:
What size wire should I use?
Answer:
The slots in the enclosure are sized for #18 AWG, but other sizes of wire can be used.
Question:
Is the TachMatch compatible with Pertronix ignition systems?
Answer:
Yes, it is compatible with Pertronix installations except for the Ignitor III models.
Question:
Does the TachMatch work with the old Sun gauges that originally used an interface box?
Answer:
The Sun 760, which used a round “puck” style interface, is not compatible with TachMatch. If you have one of those, contact Accutach.com for an interface for this application. Other early Sun tachometers, like the 765, using the “box” style interface are compatible with TachMatch.
Question:
Does the TachMatch work with the Ford TFI distributor used in many of the Ford 5.0 EFI motors?
Answer:
Yes, but there needs to be a resistor between the coil and the TachMatch. 22 kOhms works well. If this is your application, let us know when you order, and we will include the appropriate resistor.
Question:
Am I guaranteed that the TachMatch will work?
Answer:
It’s likely that it will work, but it doesn’t work in all applications. You may have noticed that there are dozens of tachometer adapters, filters, amplifiers, etc on the market. The reason is that it’s a complex problem – many variables on both the triggering side and on the tachometer side of the interface. There is no solution that always works. However, to give you an idea of your odds that a TachMatch will work, we have about 2-3 returns per 100 TachMatch units shipped out. So your odds are pretty good, about 97%, that it will solve your problem, but not 100%. If it doesn’t work, it can be returned for refund.
Question:
How do I know if I need a TachMatch V-Boost module?
Answer:
Most tachometers don’t need a V-Boost module, they will work from a standard 12v square-wave-type signal as generated by a standard TachMatch or MSD unit. But some don’t work – we see it most often with VDO tachometers, and voltage-driven Datsun tachometers, but there are some others out there too. There really isn’t a good way to know that you need one until you have first tried with a 12v signal, and it doesn’t work. The V-Boost module doesn’t always make these problem tachometers work, but it’s rare that it doesn’t.