Dear Adam,
Injectors fall into two categories, electrically speaking. Those whose resistance/impedance is lower than 4ohms are considered low impedance and those whose resistance is typically 10-12ohms are considered high impedance.
It takes 4amps to open a low impedance petrol injector, but only 1amp to keep it open. Feeding it 4amps continuously would overheat it, so it is desirable to limit the current once it is flowing fuel.
The Lucas 16CU does this by having two transistors in the driver circuit. Once hits it for 4amps for about 1mSec and then the second transistor pulses a lower current into the injector for remainder of the desired injector opening time.
The 16CU has four driver circuits and each one is connected to three injectors. It is thus batch fired in four banks of three injectors.
The MSv3.0 board has only two injector drivers. These are however more robust than the 16CU drivers and can handle six low impedance injectors apiece. This would also thus be batch fired but in two groups of six injectors. Rather than having separate transistors to handle the opening peak and the hold phases, the MSv3.0 board does this with software, whereby it is told to limit the current to a fixed percentage by flashing on and off very rapidly during the hold phase. It is strong enough to handle six injectors per driver circuit.
By contrast, a high impedance injector simply runs by using a “flat” current profile.
Ignition is a totally different topic.
The simplest setup - as currently fitted - is to have one coil which charges and discharges twelve times per engine cycle and then have a method for distributing the electrical pulse to each spark plug.
The most complicated setup is to have twelve dedicated control lines used by the ECU to charge twelve coils and discharge them sequentially to the relevant spark plugs per engine cycle. The ECU only has a simple ability to send a 5v or 12v low current control pulse out and so a transistor circuit is needed to change this into something which can charge the coils. Some coils have this circuitry built into their design and some don’t. The Ford coil packs I have used are simple standalone items, hence the additional BIP373 ignitor box.
The setup I use is called wasted spark. This uses six control lines from the ECU and feeds six double ended coils. The coils are fired twice per engine cycle. One of the pulses ignites the mixture in the conventional way and the second pulse, which is 360’ out of phase, ignites the mixture in the cylinder which fires 360’ later. Because the coils are double ended, the spark plug in the “wrong” cylinder, 360’ out of phase also fires, but there is no combustible mixture to ignite, hence the term “wasted spark”. I have chosen this setup as the best compromise between using too many of the ECUs resources and having the most functionality.
Programming the MS unit relatively straightforward, as you can start off with a mapping supplied by another user like myself and then adapt it to your own needs. It’d be much more daunting if there were no one to copy, but even then the default settings should be enough to get the engine to start and run, before the autotune features can be used to take over.
You could also consider running just a trigger wheel, a MAP sensor and a Megajolt for ignition and leaving the fuelling to the 16CU for the time being.
kind regards
Marek
