Conversion of a Buzz Coil Ignition to Modern High Tension

It’s generally not easy due to timing.

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David Cave
Figure 9: An Evac2 buzz coil replacement running a John Deere on two 9V batteries.

Often, the question is asked if an engine can be converted from a Model T-type buzz coil to some other form of high-tension ignition. Another related question is how to add a battery saving time-out to a buzz coil in case the engine stops running while the coil is running. The answer is: it’s generally not easy, due to timing.

A buzz coil engine will have a timer switch, somewhere on the engine, coupled to the crankshaft rotation. On a John Deere spark plug engine, it’s on the push rod, see Figure 1.

Typically, the timer switch has one terminal connected to the ground. Closure of that switch will complete the ground circuit for the buzz coil (or battery) and initiate a spark. The switch remains closed for some time, often 20 to 50 degrees of the crankshaft’s rotation, then opens again. This degree of closure allows the buzz coil to spark multiple times and ensure combustion. In summary, when the timer switch closes, the engine is expecting a spark.

Traditional high-tension systems reverse that order. When the switch or points of a high-tension ignition system close, the system begins creating and storing energy. When the switch or points open, the system dumps the stored energy as a spark. If a normal high-tension system were connected to the buzz coil engine timer switch, the spark would occur when the timer switch opens, 20 to 50 degrees too late.

Modern automobiles have a smart coil attached to each cylinder. The smart coil receives a signal from the engine control computer when it’s time for that cylinder to fire. Internally, the smart coil contains enough electronics to complete the task of creating a spark. The following circuit, Evac2, tricks the smart coil into believing the closing of the engine timer switch is the computer signal to fire. By fooling the smart coil this way, a spark will occur when the engine timer switch closes.

black part on light wood surface

Figure 2 is the UF 262 smart coil found in many 2000 to 2007 model year Chevys, Cadillac Escalades, and GMCs. The coil can be found on eBay for less than $20; at the local U-Pickit junkyard, it should be considerably less.

Figure 3 is the schematic of the complete high-tension ignition system, Evac2. It consists of one component, a UF 262. A red wire will be connected to pins 1 and 2, and a black wire to pins 3 and 4.

If the UF 262 is found in a U-Pickit junkyard, pull the connection plug and pig tail. Figure 4 is the completed buzz coil replacement, Evac2, using the connection plug. The connection plug is also shown as it would appear when pulled off the engine. The leads coming out of the plug are as follows: red pin, 1; green pin, 2; brown pin, 3; and black pin, 4. Shrink tubing will be placed over the solder connection for protection but left off in Figure 4 for clarity. The unit is fully self-contained and isolated, thus there is no need to put it in a box or other enclosure.

The coil mounting bracket can be removed by bending the ear tabs out and sliding it off. The red wire should be long enough to reach the battery positive (+) terminal, the black wire should be long enough to reach the engine timer switch, or the kill switch (if there is a kill switch). The high-voltage wire must be long enough to reach the spark plug. For high-voltage output, an electrical bullet connector slides onto the coil nicely. In Figure 4, the bullet connector can barely be seen poking out the business end of the coil.

If the UF 262 is purchased online and there is no connection plug available, a Dremel tool or nippers can be used to cut away the hood above the connector pins to make it easier to solder the wires to the pins. Figure 5 is a completed unit ready to put in a box.

Figure 6 is the system in the box, with the lid ready to glue on. The thumb nut attached to the red wire can be painted red and the nut attached to the black wire can be painted black. Unlike a buzz coil, Evac2 is polarity sensitive so the red wire and the black wire must be externally identifiable.

Now that the buzz coil replacement is completed, it needs to be connected to the engine. Figure 7 is a common connection schematic. The red Evac2 wire goes to the 12V battery’s positive (+) terminal; the black Evac2 wire goes to the kill switch; the other side of the kill switch goes to the engine timer switch; and the high voltage output wire goes to the spark plug. The other side of the timer switch, the battery negative (-) terminal, and the spark plug must all be attached to the engine block, which is the ground. Figure 8 is another connection and just as valid as Figure 7. In Figure 8, the red wire goes to the battery positive (+) terminal; the black wire goes to ground (engine block); and the battery negative (-) terminal goes to the kill switch. A third connection would be to put the engine timer switch where it is in Figure 7 or Figure 8, and place the kill switch where it is in the opposite configuration.

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The buzz coil replacement is efficient and effective. Upon firing, it puts itself to sleep, waiting for the next signal, thus saving battery power. If an engine happens to stop with the timer switch closed, Evac2 will not run the battery down. The spark is strong, typically able to throw a two-inch arc. For cars that use the UF 262 coil, set the spark plug gaps in the region of 0.050 of an inch. Although not necessary, the engine plug gap could be expanded to 0.050 of an inch. While shown with a 12V battery, the engine also works fine with an 18V battery, but will not work with less than an 11V one. Typical buzz coils measure 2 x 3-1/2 x 6 inches.

Evac2, shown in Figure 6, is in a box measuring 2 x 2 x 3-1/2 inches, a third of the volume of a buzz coil. Rie Fulk built a 1/3-scale John Deere spark plug engine. Needless to say, the battery box on that engine is small. A goal was to get a small battery and an Evac2, like that shown in Figure 6, in the battery box. Figure 9 is an Evac2 running a John Deere 3hp spark-plug engine using two connected 9V batteries in series (18V). Those tiny 0.5 Amp hour 9V batteries ran the engine for a bit over two hours. Not visible in Figure 9 is a capacitor across the batteries for reducing output impedance.

Dr. David Cave is a regular contributor to Gas Engine Magazine and can be reached at

  • Updated on Aug 15, 2021
  • Originally Published on Aug 12, 2021
Tagged with: buzz coil, evac, ignition system
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