Industry jargon and advice given from various sources can be confusing.
At present, there are three basic types of LPG conversion (ignoring tanks for now).
Suitable for most cars up to 1992
'Open loop' is the simplest and oldest design. A single point gas mixer supplies the engine with gas vaporised by the vaporiser according to a fixed and preset ( but adjustable) level. The gas is then mixed with air and the fuel gas is created. When running on gas either the carburretor or basic fuel injection are deprived of petrol by a fuel cut off valve, relay or electronic 'emulator'. A fuel changeover switch of one type or another will be fitted inside the vehicle.
This system is not 'intelligent', it cannot vary the fuel / air mixture according to any information available apart from its fixed settings and thus has shortcomings. That said, it is relatively cheap and ideally suited to older vehicles having a carburretor (or more than one) or very basic fuel injection. LPG economy can be quite good as long as the system is correctly fitted, its components carefully chosen, then properly set up and adjusted.
Note Open loop systems are not suitable for fitting to a vehicle that has a catalytic converter.
Note that any LPG system relying on a single point mixer will fill the inlet manifold with mixed gas and air which is potentially explosive. If anything causes the mixture to be ignited in the manifold (e.g. misfiring due to poor ignition, leaking engine valves etc.) 'Backfiring' can be the result. This risk is very low with carburreted engines, as there is little to be damaged, but much higher with fuel injected engines. It is therefore crucial that any vehicle to be converted must have ignition components right up to par, no air leaks into the inlet manifold, gas tight engine valves and other service items such as air filters in absolutely first class condition.
Suitable for MOST cars up to 1996 (but not all)
'Closed Loop' is a somewhat misused term but I use it here to help the reader understand the system from the title most likely to be picked up from others.
The system widely called 'Closed loop' is actually an Open loop system which has added to it a form of variable mixture control. The system uses a single point mixer and vaporiser very similar to the open loop system described above. The difference is in the way mixture control is handled. Although beginning from a similar fixed but adjustable set of values, fuel / air mixture can be varied by a mixture controller. The mixture controller (normally solid state electronic) reads mixture information from the vehicle's Oxygen or Lambda sensor mounted in the exhaust. The actuator (driven by the controller) is most often provided in the form of a 'Stepper motor', a type of valve that can move in and out to vary the amount of gas allowed into the engine. In this way, the 'Closed loop' system can be said to be 'intelligent' as it gathers information from a sensor and then acts upon it.
If installed on a fuel injected car the system will need an 'emulator' or two, used to switch off the Petrol injectors and 'fool' the ECU into 'thinking' that those injectors are still working. The system demands quite a lot of information to allow it to vary the mixture. Inputs from a number of sources must be provided or it cannot work, those being -
Oxygen (Lambda) sensor signal(s)
Throttle Position Sensor (TPS) signal
RPM (tach) signal
Closed loop systems must be fitted to any vehicle with a catalytic converter (cat.). An Open loop system would damage the cat. Closed loop systems are more expensive than open loop because a controller and actuator must be provided, fitted, wired in and set up with a computer and gas analyser. However, the system normally performs slightly better on fuel economy than an open loop system.
Note The problem with the label 'closed loop' is that it suggests that it is the only system that has a closed loop, which is most definately not the case. The much more complicated and intelligent systems we are about to examine are far more accurate, but still operate on a closed loop basis.
Note that any LPG system relying on a single point mixer will fill the inlet manifold with mixed gas and air which is potentially explosive. If anything causes the mixture to be ignited in the manifold (i.e. misfiring due to poor ignition, leaking engine valves etc.) 'Backfiring' can be the result. This risk is low with carburreted engines but much higher with fuel injected engines. It is therefore crucial that any vehicle to be converted must have ignition components right up to par, no air leaks into the inlet manifold, gas tight engine valves and other service items such as air filters in absolutely first class condition.
All Cars 1992 - 1999
Suitable for electronic fuel injection engines with Oxygen (Lambda) sensor, Catalytic Converter and plastic inlet manifold(s) and all Turbocharged and Supercharged engines.
Multi Point Gas Injection is also a closed loop system as it is 'intelligent', gathering information on fuel mixture from the Oxygen sensor, acting upon it to vary the mixture as it is received.
Inputs from a number of sources must be provided or it cannot work, those being -
Oxygen (Lambda) sensor signal(s)
Throttle Position Sensor (TPS) signal
RPM (tach) signal
Manifold ambient pressure (MAP)
These signals are picked up raw at source and then used by the additional gas ECU (Electronic Control Unit) to arrive at the correct mixture for the conditions. The big difference over 'closed loop' is in the way gas is fed to the engine - It will still use one or more vaporisers and emulators but there is no single point mixer in this system. Instead, gas is injected under pressure by separate injectors placed points in the inlet manifold just before the engine inlet valves, (just as petrol is injected normally).
The multi point injection system is much more expensive but brings huge benefits. It practically removes the potential for 'Backfiring' mentioned in both systems above, as no gas is present in the inlet manifold, only air. When thinking about having a late model car converted, remember that it is likely to have a plastic inlet manifold which could be literally blown to pieces by one single backfiring occurrence. This is why we would only recommend and fit a multi point injection system to such a car. In addition, this system may well prove to be more fuel efficient than any of the above mixer systems.
All cars 1992 - Present Day
Suitable for sequential and non sequential electronic multi point fuel injection engines with Oxygen (Lambda) sensor, Catalytic converter and plastic inlet manifold(s) and all Turbocharged and Supercharged engines.
This 3rd generation system has all of the attributes and benefits of the earlier multi point system. In addition, it is super intelligent and It has the ability to inject gas in a truly sequential manner, just like the latest petrol vehicles. It achieves the latest European exhaust emission requirements with ease. This has a double meaning to the LPG motorist - A car that pollutes the least can be the most fuel efficient as little fuel is wasted.
The 'N' system requires even more information from the engine but uses a lot of data from the vehicle's existing engine management instead of picking it up raw at source as the earlier system did. Additional information required is -
Petrol injector pulse length
The system also has its own ECU but this works in conjunction with the Petrol ECU, instead of working alongside it like the earlier non sequential system.
Even more benefit of performance and economy are delivered by the new Romano system, along one or two useful bonuses. The new system will 'sense' that gas pressure is low and switch back to petrol before the gas tank runs dry - A very useful trick. It will even give you an audible warning to tell you it has done this. A 'self check' protocol has been added to the changeover procedure so that the system will not move on to gas if a problem exists. The system now handles enigines up to 400 bhp with a single vaporiser which makes life easier for us and more reliable for you. Last but not least, the latest 'FAST' type injectors can be stripped and cleaned using only basic tools, no more worries about injector contamination by poor quality gas.
We installed one of the first of these new kits in the UK last week, a Jaguar XJ8 4.0 was the lucky recipient. We were not disappointed. The car was road tested for 200 miles. Performance on LPG is just the same as with petrol and one can not even tell when the system has switched over to gas. All you notice is that it saves you a fortune on fuel bills because LPG economy is as good as it can get.
The latest Romano 'N' system installed on BMW V8
The Romano 'N' system truly deserves the title 'State of the Art' and we look forward to fitting many systems over the coming months.
To see some of the cars we have already converted using this equipment, select 'Conversion Gallery' from the left bar and then select the model you are interested in.
Yes, they can be converted!
Click this link for an explanation - Turbo's and Superchargers