Tach driver, '91 Jeep Wrangler with 2009 4.7L V8
USE WITH LOW-VOLTAGE and DIGITAL SIGNALS (5v, 6V, 12V):The
UTC will work with trigger signals down to 4.1V, and can be used freely with digital or analog sensors at 12V or 5V. However, DIP-switch 7 must be turned on for the UTC to "see" the signal. The UTC will not trigger until about 25V with switch-7 in the off position.
USE WITH OEM TACH OUTPUTS:
The UTC will work with any OEM tach ouput, including GM HEI and Ford Duraspark-II systems. However, be aware that many OEM outputs (including HEI and DS-II) are actually internal connections to coil-negative, NOT 12V digital square waves like late-model ECU's. This means they produce very high voltages (up to 350V for some HEI's). Since turning
switch-7 on disables most of the circuit protection inside the UTC, connecting to voltages above 15V can destroy the unit.
If in doubt, ALWAYS start with switch-7 in the OFF position. Switch it on only if the UTC fails to trigger.
FOR FORD COP-V8 and ALL OTHER COP OWNERS:
The UTC will work with any COP system, 2-wire or 3-wire. However, if you're considering the UTC as a low-cost alternative to the MSD 8913, Autometer 9117, or similar product, be aware that the UTC does not work or wire the same way. Those units work by sensing coil current instead of coil discharge, and they wire in series with the coil power supply, not the coil trigger. The UTC is not series-wired and senses trigger voltage. When wiring the UTC, some buyers have followed threads about the MSD unit on websites such as crownvic.net, but those threads do NOT apply to this product and should NOT be followed when installing one. For instance, on a V8 Vic or Grand Marquis, threads advise getting tach signal from the LG/R (light green with a red trace) wire to the coils. This is correct for the MSD, but it is the coil power wire and the UTC cannot get signal from it.
The UTC must be hooked to the negative side of one COP coil (i.e., to any of the individual trigger wires connecting each COP to the ECU). These can be easily identified because they will have a different color wire for each coil. The coil power lead (and ground lead on 3-wire COPs) will usually be the same color on all coils.
THE UTC WILL NOT WORK IF CONNECTED TO COIL-POSITIVE LIKE CURRENT-SENSING ADAPTORS.
IT MUST BE CONNECTED TO COIL-NEGATIVE OR A COIL TRIGGER WIRE.
FOR CDI IGNITIONS:
Most aftermarket CDI boxes like the MSD 6 and 6AL have a dedicated tach output, so the UTC can be be driven driven directly off that. For CDI setups that have no tach output, signal can be taken off the spark coil, but be aware that CDI's drive the coil from the positive side, not the negative like ordinary ignitions. You can easily identify a CDI by measuring voltage on the negative pin with the engine operating, if it stays near 0V at all times then the ignition is CDI. Swapping pins is usually all a CDI requires to work with the UTC, it can otherwise be treated like any other high-voltage source. Filtering isn't usually needed because CDI spark pulses are usually much shorter than normal ignitions, so "coil ring" is rarely an issue.
FOR 3-WIRE COP OWNERS ONLY:
Most 3-wire COP triggers produce no inductive "spike" like a coil-minus connection. Most are 12V square waves. For these systems, the UTC needs to operate with switch-7 on, just like connecting to a 12V sensor. However, the same caution applies as connecting to an OEM tach output (see above): Since turning
switch-7 on disables most of the circuit protection inside the UTC, connecting to voltages above 15V can destroy the unit.
If in doubt, ALWAYS start with switch-7 in the OFF position. Switch it on only if the UTC fails to trigger.
FOR DIS VEHICLE OWNERS:
Because
the UTC senses trigger voltage, it cannot sense a DIS unit with no tach
output in the same way as current-sensing units like the MSD 8913 or Autometer 9117.
This is not a problem for externally-triggered DIS packs, because you can simply tap one of the trigger wires from the ECU, just like any COP system. The only complication compared to COP is determining the right ratio for your tach, since many DIS packs are essentially "dual fire" setups. This can be easily determined with a shop tach, simply changing the ratio switches until you find a setting that works. However, for self-contained DIS packs with an ECU onboard, you must
find an alternative trigger source if there is no ECU tach output. Crankshaft sensors can be a good
choice, provided you know the number of pulses per revolution and can
calculate a ratio that works with your tach. However, many engines
(like virtually all GM powerplants) produce too many pulses to be
usable. Camshaft sensors can be used similarly and work very well on
some vehicles--most GM LS motors have a 4-tooth cam ring that produces output
similar to a 4-cyl distributor and is symmetric enough for a steady
needle--but other engines with more asymmetric rings may produce a
"wobbly" tach at low RPMs. This is something that only experiment will tell you. Alternatively, you can produce your own trigger by adding an
aftermarket magnet/hall-sensor combo to your harmonic balancer (treat
the output like a diesel with an external pickup) or an inductive clamp
sensor on one of the spark plug wires (treat the output like COP).
In most cases, the UTC will even trigger by wrapping a wire around a spark plug lead. The UTC is not fussy about signal level (any voltage from 4.1-200V will
work), but it must see a change in voltage. If you have no suitable signal source, then the UTC will not work for you.
FOR POINTS-IGNITION OWNERS:
Points ignitions can be almost as "noisy" as magnetos, especially as the points age.
Various spikes on the line can cause symptoms from double-triggering at
low RPM to complete blanking at high RPM. For this reason, the UTC has a built-in RC (resistor-capacitor) filter that you
can turn on with one of the DIP switches. The built-in value is 100K/0.1uF,
but you can increase the filtering simply by adding one or more of the resistors included with the kit.
FOR MAGNETO IGNITION OWNERS:
The UTC has an RC filter for controlling noise (see POINTS above), but it also needs a DC power source to operate, as do all electric tachometers. If your vehicle has DC lights, a battery, or both, then you should be able to run the UTC and an electric tach off the electrical system. This includes most magneto-ignition motorcycles that have a headlight but no battery, since these generally have a low-voltage "lighting coil" built into the magneto that can be tapped for DC voltage. If your vehicle has AC lighting (like some snowmobiles) or no lights and no battery (like most motocross bikes and push lawnmowers), then it may not be possible to add a tach without also adding a DC conversion kit or other specialized hardware to provide a DC supply.
FOR ANTIQUE IGNITIONS:
The UTC will work with all 6V systems and with positive-ground systems. For positive-ground, simply reverse the power and ground pins on the UTC, connecting +V to ground and ground to +V. If your trigger is coil-negative, hook a 6V system up just like 12V and leave switch-7 off. However, if your trigger is a 6V level square wave from the system rail, you MUST use it with switch-7 ON.
FOR OWNERS OF 24V and "BACK-EMF" TYPE TACHOMETERS:
Many older tachs require greater than 12V to trigger, expecting to see the "spike" from a discharging ignition coil. Since the UTC outputs a 12V square wave, it can't drive these tachs without help. What is required is a "coil simulator" (aka "kicker coil") on the UTC output. This is just a high-voltage transistor connected to a small inductor like a relay coil. If you own one of these tachs, you can either purchase a weather-sealed kicker along with your UTC (see my EBay listing# 142171581596) or I can provide a schematic and parts list free of charge if you'd like to build one yourself. If you aren't sure, tapping the tach trigger wire on the battery+ terminal will usually tell you -- if the needle jumps or quivers then 12V will probably trigger it, if not then you probably need a kicker.
FOR RVI AND OTHER CURRENT-SENSING TACH OWNERS:
Many
antique English cars and other older makes used coil-coupled
tachometers operating directly off the ignition points. Instead of
voltage, these tachs sensed current flow through the points to ground,
using the induced voltage to deflect the needle directly. Many snowmobiles also use current-mode tachs, driven off one leg of the magneto or lighting coil. The UTC can't
drive this type of tach on its own, since it can output only milliamps
of current (by contrast, a typical "toroidal" RVI needs an amp or
more). However, in theory, the UTC should be able to drive a simple
current amplifier (such as an N-FET or NPN power transistor) to provide
enough current, essentially "pretending" to be the ignition points. One
of my buyers planned to explore this on his re-motored MGB, but his RVI
proved to be burnt-out. If you are good with solder and have an RVI
or other current-mode tach that you would like to try driving with the UTC, I will offer a
schematic, parts list, and continuing advice free on request.
NOTE: Units may come with clear potting (shown) or black. There is no functional difference and the shipped unit may be either color.