Points to Electronic Ignition Cheap & Easy
Any engine with a 12volt point ignition can be converted to electronic ignition using a Ford TFI module. It is both cheap and easy. Point ignition is a simple example of a digital system. Simply put when the points open the voltage is interrupted on the primary side of the coil and induces a voltage in the secondary. This means that the expanding and collapsing field of the coil is switched off and on by the points opening and closing. If a capacitor is not wired in parallel to the points they would burn out quickly, hence the condenser(cap).
In a regular point ignition the points are a switching device. The idea here is to change the points from a switching device to a triggering device and make the module do the switching. Switching a coil on and off is where the heat is generated and that is what causes the points to burn out.
Of all the digital ignition modules used in automotive applications the Ford TFI is the only common module that fires on the negative to positive transition of the waveform. Since points fire at the same time they can be a good triggering device for the TFI ignition module. Just visit the local auto bone yard and get several Ford TFI modules along with the heat sink, and plug-in. I usually cut off as much of the harness as possible with the plug. It is important to get a module and heat sink pair like the one pictured. The earlier model mounted directly to the distributor and though will work it is more difficult to mount and the wiring is a little different
Looking directly at the module the bottom right would be wire #1. The illustration spells it out clearly (I hope). I usually just take #3&6, tie them together and hook them to the positive side of the coil seeing that is keyed ignition. #1 to ground, and #5 run to the points. Now you have an electronic ignition that will definitely not work!!! If you disconnect the condenser it will work flawlessly. Again you MUST make sure there is no condenser hooked to the points. The points need only to close and open, the gap is irrelevant
If you just set up a battery on a bench and hook up all the wires as shown you can check the spark by toggling the point lead (#5) with a test light hooked to ground. You will get a nice hot spark out of the secondary. I have pictured one of my forklifts that I did the other day. It really is quite simple and works well on older motorcycles. Single and twins will work fine on one module, but fours need two. Rule of thumb is one set of points one module, two points two modules.
thats cool!
although I generally use the GM HEI module ( $15) and ford TFI coil ( $30)
when I do similar conversions.
Hey cool, thanks for posting it.
I've put a couple chrysler modules inline back in the day, the old firewall mounted ones but as you mentioned they triggered on close, so you'd have to turn the distributor so the points would time on closing, on the backside of the cam.
While I agree that gap is not critical for spark, it is important for the dwell angle and so you should at least try to approximate the point gap
In my experience the HEI being analog works quite well with any analog triggering device like a pulse generator. The four prong old style ones I used for everything from a Jaguar 12's to a Mazda rotary engine. Being that they have a pulse type trigger in the distributor they will cause the module to switch whenever it senses the triggering signal change from positive to negative. I have never tried them in a digital setting, but it is interesting that you mention them working. I have never changed the coil unless the old one was bad.
Thanks,
I had considered the method you mention with other modules, but not all distributors have enough of an arc to allow for timing also. While dwell is controlled by gap in a contact breaker system in the TFI module it is controlled by the current limiting circuit.
I appreciate your method, it answers an old question I have had in the back of my mind for years.
Thanks,
years ago, I rigged an ould outboard motor up with an HEI module ( 4 pin)
outboard ignition, had a distributor, with a hall effect trigger.
researched the IC used in the GM module, motorolla dont remember the part number.but it required less than 0.3 or 0.03 voltage differential to trigger.
not much at all.
I routed 12 volts thru the hallefect trigger, simply as a signal voltage, and picked it up on the switched side with the HEI module.
there were a couple of 10watt resistors in there to pull it to ground also.
it worked well, that HEI module is a very useable, well designed unit that is available CHEAP.
it needs a heatsink though, to really live long, and its a bit current hungry, 4-6 amps if I recall to sting the coil.
the ford TFI coil seemed to have the best wind ratio and internal resistance to run cool and give a big spark with the HEI.
again, YEARS ago, my memory isnt so good
This is good information. It makes sense to me that the HEI would work well the way you describe seeing it would also fire on the negative to positive transition. It would also work on motors that do not have a distributor like the TFI does. A real plus.
I have used them in the past on any analog distributor. I once used one on a Mazda rotary engine that had two modules mounted on the dist. Since the modules themselves cost over $400 each we looked for an alternative. We also found that a little dia-electric grease on the back and the firewall as a heat sink worked sufficiently. The four prong modules used in the early Chevy's worked best as I remember. My method was to test the output on the distributor's pickup with a VOM on AC voltage. Just hook to the two wires coming out of the pickup to both leads of the VOM and spin it over. If you get voltage it works and will trigger the module. If no voltage.....pick-up bad.
One time years ago a shop called us with a Jaguar 12cyl that would not run. I tested the pick-up and it was good. I informed the manager that the module needed to be replaced and I could do it cheap with a Chevy HEI and save the customer a bunch (the Jaguar module was just under $500). The customer wanted the OEM module. I was ready to order one from the dealer when just out of curiosity I decided to open up the original module. It was an aluminum box about 3x6 inches with a power transistor mounted on the side and you guessed it, inside was an HEI module. Yup fixed it for about $20!
Generally I try not to replace coils on older applications because sometimes the hotter spark will cause older distributor caps to arc and they can be a bear to find
The $25 (per points set) points-triggered electronic ignition
Courtesy of GM's effective and inexpensive HEI module.
To my visitors:
If you're building one of these I would appreciate it
if you would Email me with your experiences.
I don't like points for a number of reasons, but I own a lot of old motorcycles so I have a lot of points. I'm experimenting with the 7-pin GM HEI module as a drop-in points triggered alternative. I have successfully run a 1965 Ducati 250 and a 1975 Honda CB400F using HEI modules.
Although will I still have points, they will carry only a few milliamps of current so they will never need replacement. They will need adjustment only to compensate for wear on the rubbing block which can be reduced by increasing the points gap. I'm currently running them without condensers.
A points ignition wastes most of the current it consumes at low rpm because the dwell time controlled by crank angle, not by the amount of time it takes to charge the coil which is essentially constant regardless of rpm. The excess power is wasted heating up the coil. The GM HEI controls the dwell time by measuring how long it took the coil to saturate on the previous cycle. If the coil did not reach saturation, the HEI turns the current on a little sooner, if it reached saturation too soon, the HEI delays a little longer for the next cycle. This is a big advantage for older motorcycles which often have marginal alternator output, since at low rpm when the alternator is putting out little current, the HEI controlled ignition uses much less than a conventional points ignition.
My Circuit
I'm strictly a hobbyist, so there may be a better circuit for this, but so far, this is working for me.
The 7-pin module was used on many GM cars and trucks in the 80's and 90's. I order a module for a 1985 Chevrolet El Camino with a 5L V8 and 4bbl carb because I like El Caminos. The module requires 5 volts on pin B, and on the trigger pin (pin E). The ignition fires when the signal on pin E goes from 5 volts to 0 volts. Because the current required is very small and the HEI is quite tolerant of voltage variations, you don't need a complex power supply, the resistors and the zener diode are sufficient to provide the appropriate voltage on each pin. I'm tempted to try dispensing with the zener and applying 12 volts to the pins with a resistor to limit the current through the points, to see if it would hold up.
I used the circuit below on my 1965 Ducati 250. I retimed the points cam drive shaft (12 teeth counter-clockwise) so that I could time the ignition to fire when the points close rather than when they open. I used a slightly different circuit with two HEI modules on my 1975 Honda CB400F Super Sport. On the 400, I swapped the points leads (1-4 for 2-3) which allowed me to time the ignition to fire when the points close.
There are other ways of wiring the HEI up using something like an optoisolator or a photovoltaic isolator that would allow me to design a circuit to trigger the HEI when the points open as in a conventional points ignition.
So far, I've found one caveat to this arrangement. It sometimes fires when I first apply power to the ignition, as when I turn on the key. I can imagine some circumstance where when the engine was last run, the piston stopped at just the right position with a cylinder full of mixture and this unintended spark could ignite the mixture in the cylinder. There's probably a workaround for this, but I'm not sure it's really worth complicating the circuit.
This is a shot of the HEI (partially) installed in my Ducati 250. I like to use molex connectors to mount electronic components. I will coat the connectors with liquid electrical insulation and wrap them with electrical tape when I'm satisfied with the results of my tests.
Some people claim you have to have a fancy heat sink for the HEI module. You don't. I ran an HEI in a 240Z for years mounted to a simple aluminum plate like the one here.
Better Dirt Cheap Electronic Ignition
The Chrysler ignition module is cheap and easy but it is ancient technology. The dwell control is crude and it relies on a ballast resistor to limit current. It is lower maintenance than a set of points but the performance isn't any better. To get more power out of an ignition system you need a coil with a higher inductance and you need to pull more amps through it. Increasing the primary current requires better dwell control to prevent burning out the coil.
Ford created the TFI (Thick Film Ignition) for use on fuel injected engines. There are two types of TFI systems; TFI-IV and TFI-CCD. TFI-IV has a dwell control built into the ignition module. Most TFI-IV modules were gray. A TFI-CCD relies on the computer for dwell timing. All TFI-CCD modules were black. Both TFIs were available in closed and open bowl configurations. Early TFIs were mounted to a hole in the side of the distributor housing, these were called open bowl. They had trouble with the modules blowing out so they started mounting them on a heat sink away from the distributor, these were closed bowl systems. Pictured is an open bowl TFI-IV module mounted to a heat sink. The closed bowl modules look identical except they don't have the three quick disconnects coming out of the top. Most guys don't use the TFI because it relies on the computer for ignition timing, there is no mechanical or vacuum advance. I designed a stand alone digital ignition control which plugs right into a TFI distributor and allows full control of the ignition curve. Although, you don't need a computer to use a TFI-IV.
I bought an open bowl TFI-IV distributor at a swap meet for $10. It came complete with a module, plug wires, and a brass terminal cap. I also found a TFI coil for $6. The TFI was the perfect setup for my digital ignition. When trouble shooting my ignition I bypassed the computer and set the base timing to 36°, remember with no computer the advance doesn't change. Surprisingly it ran great with the advance locked out. When I was at the drag strip I ran it both with and without the computer advance and it made no difference. I would recommend anyone building a budget drag car to just slap in a TFI-IV distributor and coil. The distributor is easy to hook up, pin 4 is wired to the positive coil lead and pin 5 is wired to the negative coil lead. The positive coil lead is also wired to get power when the ignition switch is on. Not all cars will work well with the timing locked out. My car is only 3,000 pounds, has a 4-speed, 4.11 gears, and I don't lug it. If you have a heavy car, tall gears, or an automatic with stock converter then you will need some sort of advance. The only problem with having the ignition locked out is starting the motor. It won't want to turn over because the burning fuel will try to push the pistons down before the reach the top. The easy solution is to hook up a kill switch that grounds out the negative coil lead. I ran the coil wire to the back of the cigarette lighter. Of coarse, I removed the power wire from the lighter first. When the lighter is pushed in it shorts out the coil and kills the ignition. To start the car I would push in the lighter, then turn the motor over. When it was spinning I'd pull out the lighter and it would fire right up.
If you need some sort of advance, or don't want to mess with a kill switch, the TFI module can also be hooked to a breaker point distributor. The breaker points put out a nice digital signal like the Hall sensor in the TFI distributor. Since the module handles all the current burnt points will be a thing of the past. The points will also go years between adjustments since the dwell doesn't matter. Normally, the open bowl TFI module uses the distributor housing as a heat sink. I modified a heat sink from an Athlon processor to take the place of the distributor housing (pictured above). I mounted the module under the dash to keep the engine bay looking stock. You could also use a closed bowl TFI-IV module. If you get one from a junk yard it will have a heat sink on it. They are both wired the same. Pins 1 and 4 go to the positive coil lead (which gets power when the ignition switch is on) and pin 5 goes to the negative coil lead. Wire pin 2 to the breaker points. The module should be grounded through the mounting surface but a wire from pin 6 to ground will assure a good connection.
Can I hook a TFI to a Duraspark (magnetic pickup) distributor? No, the TFI module has a "digital" input so it won't recognize the "analog" signal from the magnetic pickup. However you can use a GM 4-pin HEI module. The HEI and TFI are basically the same thing but the HEI has the proper input for a magnetic pickup distributor. You can buy a 4-pin HEI module at any auto parts store. If your parts guy doesn't know what that is then tell him you need an ignition module for a '78 Camaro with a 350. The one pictured is a Car Quest #21040 and cost me $17.77. As you can see it has 4 pins labeled W, G, B, and C. G is a 3/16" male quick disconnect the rest are 1/4". The mounting surface must act as a heat sink to prevent the module from burning up. The cooler you keep the module the longer it will last. Securely mount it to a flat metal surface or bolt it to a big heat sink. There are two pins on the back of the module that you need to break off so it will sit flat. The module comes with some heat sink compound, smear it evenly over the back before bolting it down. Pins W and G go to the magnetic pickup. On a Duraspark distributor the purple wire runs to pin G and the orange wire goes to pin W. Run the black wire to one of the mounting screws on the module, this gives the module a good ground connection. The module must be grounded to work properly. You can plug into the Duraspark distributor connector with standard 3/16" female quick disconnects. Pin B on the module is run to the positive coil lead (which gets power when the ignition switch is on) and pin C goes to the negative coil lead.
The TFI upgrade only cost me about $40 and there was a noticeable improvement in performance. The engine runs much smoother and it pulls harder above 5,000 rpm. The TFI is a cheap performer but it isn't perfect. They are notorious for blowing out. Mounting it inside the car with a big heat sink will help but if you are not using points then carry a spare module in the glove box. If you are using points and it blows out then you can just hook the coil straight to the points and keep going.