Final version Appeared In Gas Engine Magazine Oct/Nov 2021

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. A related question, also often asked, is how to add a battery saving time-out to a buzz coil in case the engine stops running with the coil running. The answer to the first question is that it’s generally not easy due to timing.
A buzz coil engine will have a timer switch somewhere on the engine coupled to crankshaft rotation. On a John Deere sparkplug engine, it’s on the push rod, Figure 1. Typically, the timer switch has one terminal connected to ground. Closure of that switch will complete the ground circuit for the buzz coil (or battery) and initiate sparks. The switch will remain closed for some time, often 20 to 50 degrees of crankshaft rotation, then open again. The 20 to 50 degrees of closure allows the buzz coil time to get off multiple sparks ensuring combustion. In summary, when the timer switch closes the engine is expecting a spark.

Figure 1. John Deere buzz coil timer switch.

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 that 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.

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

Figure 2 The UF 262 smart coil.

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

Figure 3. The buzz coil replacement, Evac2, schematic.

If the UF 262 is found in a U-Pickit junk yard, pull the connection plug and pig tail. Figure 4 is the completed Evac2, buzz coil replacement, using the connection plug. The connection plug as it would be pulled off the engine is also shown. 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 were left off in Figure 4 for clarity. The unit is fully self-contained and isolated thus 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 + 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 sparkplug. For the high voltage output an electrical bullet connector slides onto the coil very nicely. In Figure 4 the bullet connector can barely be seen poking out the business end of the coil.

Figure 4. Completed Evac 2 with connection plug.

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

Figure 5. Completed Evac2 with wires soldered directly to coil pins.

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

Figure 6. Evac2 in the box ready for the lid.

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 Evac 2 wire goes to the 12V battery +, the black Evac wire goes to the kill switch, the other side of the kill switch goes to the engine timer switch, the high voltage output wire goes to the sparkplug. The other side of the timer switch, the battery – terminal and the sparkplug must all be attached to the engine block which is ground. Figure 8 is another connection just as valid as Figure 7. In Figure 8 the red wire goes to the battery + terminal, the black wire goes to ground (engine block), the battery – 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 but put the kill switch as in the opposite Figure.

Figure 7. Evac2, buzz coil replacement, connection to the engine.

Figure 8. Alternate connection of Evac2 to the engine.

The buzz coil replacement is very efficient and effective. Upon firing, it puts itself to sleep waiting for its 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 very strong, typically able to throw a two-inch arc. Cars that use the UF 262 coil set sparkplug gaps in the region of 0.50”, although not necessary the engine plug gap could be expanded to 0.050. It is shown using a 12V battery, it also works fine at 18V, it will not work on less than 11V. Typical buzz coils measure 2X3 ½ X6 inches. Evac2 shown in Figure 6 is in a box measuring 2X2X3 ½ inches, 1/3 the volume of a buzz coil. Rie Fulk built a 1/3 scale John Deere sparkplug engine. Needless to say, the battery box on that engine is very small. A goal was to get a small Evac2 like that shown in Figure 6 plus a battery in his battery box. Figure 9 is Evac2 running a John Deere 3 hp sparkplug engine using two 9V batteries connected 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.

Figure 9. Evac2, buzz coil replacement, running a John Deere on two 9V batteries.