How a Lovato Sequential Injection System Works: ECU, Reducer, Injectors and Switch

A Lovato sequential injection system runs a petrol engine on gas by injecting timed pulses of vaporised gas at each intake port, one gas injector per cylinder, under its own gas ECU. It is called sequential because the gas is injected in step with the engine’s own injection sequence, not dumped into the manifold in one place. This is the modern standard, the same architecture people call fourth-generation autogas, and it is why a well set-up gas system drives almost the same as petrol. Understanding what each part does makes fitting, tuning and fault-finding straightforward.

This note walks through the components and how they work together.

The gas ECU: the brain that reads petrol and doses gas

The gas ECU sits alongside the vehicle’s own petrol ECU and does not replace it. It taps into the petrol injector signals to read how long the petrol ECU wants each injector open, which is the engine’s fuelling demand for the current load and speed. From that injection time, plus the gas pressure and temperature it reads from its own sensors, the gas ECU calculates the equivalent gas injection time and drives the gas injectors for that long.

While gas is selected, the gas ECU emulates the petrol injectors: it keeps them from firing but feeds the petrol ECU the signal it expects, so the petrol ECU sees no missing injector and logs no fault. The gas ECU also talks to the vehicle over OBD during setup, so it can read engine data and be tuned to the specific engine. The result is that the standard engine management still runs the show for timing and closed-loop control, and the gas ECU translates its petrol demand into the right gas dose.

The reducer: dropping tank pressure and vaporising

The reducer is the heart of the gas supply. On an LPG system it is a vaporiser: it takes liquid LPG from the tank, drops the pressure and turns it to vapour, using engine coolant piped through the reducer to supply the heat that vaporising needs. On a CNG system the reducer is a high-pressure regulator, stepping the tank’s roughly 200 bar down to working pressure in stages, again warmed by coolant because a large pressure drop chills the gas.

Either way, the reducer’s job is to deliver gas as a stable vapour at a regulated working pressure to the gas rail. If the reducer is undersized for the engine’s power, it cannot keep up at full load and the mixture leans out on the top end. That is why the reducer is sized to the engine, not fitted as a one-part-fits-all.

The gas rail and injectors: timed delivery at the port

From the reducer, vapour passes through a gas filter to the gas rail, a manifold carrying one gas injector per cylinder. Each injector feeds gas through a short hose to a nozzle in the intake tract close to that cylinder’s intake port, so the gas arrives where the petrol injector would have delivered petrol. The gas ECU opens each injector for the calculated time, in the engine’s firing sequence, which is what makes the delivery sequential and even across the cylinders.

Two sensors keep the dose honest. A gas pressure sensor (usually a combined MAP and gas pressure unit) tells the ECU the actual rail pressure against manifold pressure, and a gas temperature sensor tells it how dense the vapour is. Warm, low-pressure gas is less dense and needs a longer injector pulse for the same mass, so the ECU corrects the injection time from these two readings continuously.

The changeover switch: the driver’s control and gauge

On the dash sits the changeover switch, the one part of the system the driver touches. It selects petrol or gas, shows which fuel is running, and carries an LED gas-level indicator fed from the tank sender so the driver can see how much gas is left. It also signals when the system is warming up and not yet ready for gas.

The switch is how the handover is managed: the engine always starts on petrol, and the system moves to gas automatically once conditions are met, with the switch reflecting the state and letting the driver force petrol if needed.

How the engine hands over from petrol to gas

The sequence on every start is the same:

1. The engine starts and runs on petrol, so it always has the easy cold-start behaviour of the petrol system.
2. The gas ECU watches the reducer temperature (it needs coolant heat to vaporise cleanly) and the engine speed.
3. Once the reducer is warm enough and the revs are in the changeover window, the ECU switches fuel cylinder by cylinder from petrol to gas, so the transition is smooth.
4. From there the engine runs on gas, the gas ECU dosing to match the petrol ECU’s demand, until you stop or select petrol.

Starting on petrol and only moving to gas once warm is deliberate: cold vaporising is poor, and a cold start on gas runs rough. Letting the engine warm on petrol first is what gives a good conversion its clean drive.

Why the parts have to be matched

A gas system doses correctly only when the reducer, the injectors and the ECU are matched to each other and to the engine. The reducer has to be sized to the engine’s power, the injectors have to flow the right amount for the cylinder’s fuelling and be set to the correct calibration in the ECU map, and the ECU has to be tuned to that specific engine on OBD. Mix a small reducer, the wrong injector flow rate and a generic map and the system either runs lean at load or rich at idle, and the drive suffers. Fit the matched kit for the engine, set the injector calibration, and tune it, and it reads and doses true.

How to order or request a quote

Tell us the vehicle, the engine, the cylinder count and the power output, and we will confirm the matching Lovato reducer, gas rail and injectors, ECU and changeover switch, with the lead time. Order genuine Lovato components by part number on Omnipart.