If you're thinking about boosting your MX-5 NA 1.6 115 HP, there's one thing you need to know – the stock injector setup might give you some trouble.
Why?
In this engine, the injectors run in a semi-sequential setup, meaning they are paired: 1-3 and 2-4. When one injector fires, the other in the pair fires as well. This means that for a given pulse width, paired injectors deliver twice as much fuel as in a fully sequential system.
And here’s the catch – because paired injectors deliver fuel in double doses, the required injection time in semi-sequential mode has to be shorter than in a sequential setup. When you install higher-flow injectors (which is necessary for turbocharging), the required pulse width becomes so short that the injectors may struggle to operate consistently, especially at low loads (idling, cruising).
The fix?
Easy - rewire injectors 3 and 4 to separate outputs. If you're using my Speeduino PnP NA, you - apart of rewiring which is necessary - just need to switch the firing mode.
Stock injector wiring in the MX-5 NA 1.6 115 HP:
- Pin 2U - injector 1 and 3
- Pin 2V - injector 2 and 4
Corrected wiring (same as NA 1.6 90 HP & 1.8 130 HP models):
- Pin 2U - injector 1
- Pin 2V - injector 2
- Pin 2Y - injector 3
- Pin 2Z - injector 4
How to do it?
For injectors 3 and 4, simply move the signal wire from the ECU (originally coming from pin 2U or 2V) to the new dedicated output. The 12V power wire stays unchanged.
A simple mod that can save your turbo project from low-RPM headaches! 🚀
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It would seem that an alternative way to extend the injector opening time is to change the “Squirts per engine cycle” parameter from 2 to 1. In that case, the injectors would operate half as often, so the required opening time to deliver a given amount of fuel would be longer. However, it doesn’t seem like the engine could run smoothly in such a scenario. The average fuel amount over time would be correct, but the instantaneous amount would not—consecutive cycles would alternately be too lean and too rich. This doesn’t seem like a good idea, especially under boost. It is definitely worth using sequential injection control if possible.