ThePaetsguy
Member
So plate mounted to a spinny thing with the pickup gapped above it timed correctly.
I’m trying to research weather it can be fired from points as asked above.
Briggs 5hp cdi ignition
- Thread starter ThePaetsguy
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I’m trying to research weather it can be fired from points as asked above.
ThePaetsguy
Member
Could these cdi’s fire an injector instead of a spark plug?
Not really. They need pulse width changes to control the fuel, the timing isn’t as important.
You’d need to do some electrical voodoo as well because injectors run a constant hot 12v line and are controlled by grounding.
You can use the magnet to send a crank signal to an ECU. This along with throttle position can give you a very basic form of fuel injection, tuning would be tricky but it would work. Ideally you want at least a MAP sensor so you have a better indication of engine load.
The downside to using a single trigger flywheel is that controlling ignition (via an ECU) is very sloppy. Ideally you want a trigger pattern for more control over ignition and if you really want to get away from wasted spark you need a cam sensor too.
Here’s a fuel only setup I tried on a Briggs 206. Ignition is still being controlled by the original PVL coil and I mounted a separate VR sensor (Axle speed pickup from a Mychron) for crank signal to the ECU
ThePaetsguy
Member
If you wire two coils Into one CDI it would dump a spark to both plugs??
Edit: they make duel CDI coils
Edit: they make duel CDI coils
Last edited:
KartRacer89
Member
I'll use a modern EFI diesel engine for reference here. The electronic injectors on most diesels in use today is a variable voltage pulse width solenoid that opens and closes the injector, it uses various signal inputs to the engine ECU, which then modulates the signal voltage to the injector coil so it's not always getting straight 12 volts, the voltage is varied so the coil moves a certain amount and injects the correct amount of fuel according to engine load, throttle input, current engine speed and other parameters. Across multiple injectors on multiple cylinders.
The pulse coil that triggers the CDI to fire is basically a hall effect on/off switch whether it's an AC or DC CDI system. When the "trigger spot" on the flywheel passes the pulse coil, a small AC voltage is created, usually 1 to 3 volts and that signal "tells" the CDI to release the stored "charge voltage" (battery or stator) to the ignition coil and then the plug fires. The CDI is discharging a pre determined stable voltage to the ignition coil. DC CDI output to the coil is going to be 12-13 volts, while AC output is usually 25 volts or higher, sometimes upwards of 100 volts. The CDI would have to be reconfigured to send a variable output signal voltage in order to run a PWM injector correctly, instead of a steady voltage.
But don't let that stop you from figuring it out. I like to see people push their brains and think outside the box.
As for using dual coils off one CDI, typically the ignitor (CDI unit) has a separate wire for each coil. For example, an inline twin cylinder has 180 degrees of crank rotation between firing each cylinder and can either use a single pulse coil with offset "trigger points" on the flywheel, or two pulse coils 180 degrees apart using the same trigger spot on the flywheel. Basically two ignition circuits in one system.
KartRacer89
Member
Probably. Are you talking about using two spark plugs on the same cylinder? In that case I would suggest having a matched pair of coils resistance-wise. Electricity follows the path of least resistance, if one coil has lower resistance the signal voltage will go to that one and the other coil may not fire its plug. The other problem you could face is not enough output voltage from the ignitor to fire both coils at once. There are ignition coils that have a single input wire and dual plug wires, that would work.
ThePaetsguy
Member
Say can I pick your brain again so I’m definitely not in any position to create a fuel injection system...
But back onto the subject instead of wiring the CDI pulse wire to the coil post couldn’t you wire it to the injector ground wire and give the injector constant 12v??
I was studying those timing adjustable CDI’s and thought about how you can set it so the advance is low at low cruising rpms’s and it will advance till max as rpm’s raise.. Or you can add a bunch of advance down low and it will already have a bunch of extra timing off the line and will raise till the max of the curve as rpm’s raise.
I figured the adjustable pulse being used on the injector ground wire would make it so lowering the Timing at low rpm’s would ACTUALLY lower injector fuel output in the low rpm’s and it would raise as needed. Instead of the pulse dumping a spark at the coil it just pulses an injector ground?
The CDI changes when the pulse happens in relation to crank position. Generally speaking the duration/length of the pulse doesn’t change, at least not in a controlled way.
For an injector it’s the length/duration of the pulse that controlled in ms. Shorter pulse, less fuel, pulse length increases with the fuel demand. For fuel you need to control how much is going in, vs when the fuel goes in. Technically the timing of the injection matters, but you can get away with spraying and spraying.
For an injector it’s the length/duration of the pulse that controlled in ms. Shorter pulse, less fuel, pulse length increases with the fuel demand. For fuel you need to control how much is going in, vs when the fuel goes in. Technically the timing of the injection matters, but you can get away with spraying and spraying.
ThePaetsguy
Member
I got a bracket from a 1973 Gilbert set. And a ton of info from Jay and Bob.. I’ll shorten that coil bracket bolt so it doesn’t need a spacer.
