6/22/2018 3:04:19 PM
Total Active User: 1
NGV Introduction
Community Forum
Community Library
Legal Actions
Contact Us
NGV 101 Section   

CNG-NGV Conversion on Sequential EFI Vehicle (EFI SIS 101)



Written and Presented by Dr. Xander Thong (MVLK Certified Gas Installer, Malaysia)







S-EFI Cars





CNG-NGV Conversion on EFI-Type Engine for petrol (gasoline) vehicles. This type of conversion is 3rd Generation, employing the Gas Metering technology, called Sequential Gas Injection System (SIS). It primarily involves a CNG-NGV injector, sophiscated Gas ECU, CNG Cylinder, built-in Injector Emulator, Pressure Sensors and accessories.




Picture Source: www.landirenzo.com


SIS CNG Conversion




Any EFI vehicle can be converted with the latest 3rd Generation Technology, or commonly referred to as the Sequential Gas Injection System (SGIS) or Sequential Injection System (SIS). The techology employs Fuel Metering Technology, based on Stoichiometric measurement. It is known to be more superior to Gas Carburetion (Air-CNG Mixer method) in terms of reliability, performance and is engine backfire-free. 


(a) CNG Cylinder (ISO11439 rating), cylinder mounting bracket + high-tension bolts & nuts;

(b) CNG-grade Pipeline, gas venting hoses + accessories;

(c) CNG Solenoid, Manometer (Pressure Gauge), CNG SIS Reducer + CNG SIS Regulator kit;

(d) SIS CNG Injector units (+ Gas Injection Filter, in some cases) 

(f) NGV Refilling Valve;

(g) Master Shut-off Valve at cylinder (PRD) and refilling valve

(h) SIS Switch-over (or Fuel Selector switch);

(i) Petrol Injector Emulator (built-in);  

(j) Timing Advance Processor (for Gas Spark Ignition Timing);

(k) Signal from Oxygen (Lambda) Sensor and Throttle Position Sensor (TPS);

(j) SIS Electronic Controller Unit for Sequential Gas Injection - Injection Mapping; and

(k) Pressure sensors for SIS.




 Picture Source: http://www.vanmeenen.com


Sequential CNG Layout

 CNG\LPG Sequential Injection System : CNG Reducer Vs LPG Vaporiser





CNG Injector (Key Component)


CNG Injector is the key component in the CNG-NGV Conversion with SIS Technology. Most EFI vehicles can be converted with SIS NGV kit, which the only difference lies with the number of injectors involved. SIS NGV kits are manufactured with 3, 4, 6 , 8 and some 12 cylinders configuration. The SIS CNG Injectors perform a similar function like the vehicle's original petrol injector. It meters the volume of CNG to be injected into each combustion cylinder based on the reading from the TPS, Pressure sensors and Oxygen sensor (or stoichiometric reading). It mimicks the injecion function of the vehicle's original ECU on the opening and closing petrol injectors during petrol driving, and the SIS ECU adapts these patterns onto the CNG injector. In layman's terms, SIS ECU read, learn, program and behaves as closely to the petrol injection patterns as possible, when operating in NGV mode.  



Picture Source: www.landirenzo.com


SIS Injector 1

 Rail CNG Injectors (Type 1)




SIS Injector 2

Rail CNG Injectors (Type 2)

(there are over 10 types of injectors available)






A good CNG Injector is commonly constructed with composite metal material which is capable of resisting extreme heat and engine temperatures.   Present CNG sequential injection systems are commonly using the Port Injection method where one CNG injector is installed for each cylinder. An exhaust oxygen (lambda) sensor is utilised to obtain Air-Fuel ratio reading and the SIS ECU calibrates the best injection volume per cylinder in obtaining a stoichiomertic reading of 17.2.


Picture Source: www.ngv.com.my


CNG Injector Design

CNG\LPG Injector Design (CCCS or PCCS Application)





This type of SIS CNG-NGV Conversion is possible as most modern vehicles operate on a closed loop control of the fuel injection (particularly in petrol\gasoline). Some SIS CNG-NGV systems require the gas injectors to be mounted directly on the intake manifold, within 100mm of the inlet valve. This system is called Close Couple CNG System (CCCS).



Picture Source: www.ngv.com.my


 Close Couple CNG System

CCCS - Gas Injectors Directly on top of Intake Manifold   






Alternatively, a second CNG system (or known as the ‘pipe coupled CNG system’ or PCCS) is the identical function to the CCLS but the injectors were not mounted directly on the manifold. Instead the injectors are connected to the intake manifold by flexible hoses. The hoses/pipes are used so the injectors could be mounted in a more convenient place. Most (if not all) SIS kit Manufacturers offers PCCS as their standard equipment as it is most compatible with any modern vehicle.




 Injector Drilling Hole

Insertion of Gas Giggler (Injection Point) and connected to Hose





Fuel Injection Spraying Pattern

Fuel Injection Dynamics






Pipe Couple CNG System - 2

 Gas Injectors Connected by Hoses onto Intake Manifold - Citroen (Side View)





Pipe Couple CNG System - 3

 Gas Injectors Connected by Hoses onto Intake Manifold - Honda (Front View)




Pipe Couple CNG System - 4 

 Gas Injectors Connected by Hoses onto Intake Manifold - Toyota (Front View)










The Sequential Gas Injection Technology employs the Fuel Metering method, where SIS Electronic Unit (ECU) determines the exact volume of gas to be injected into each cylinder. The CNG Reducer functions to de-compress the 3,000 psi CNG from the cylinder to a manageable 40-70 psi levels. Subsequently, the low-pressure CNG gas is distributed by the CNG Regulator (as well as regulating a constant gas pressure) to the Gas Port Injectors. Each Gas Injector are pressurized to 40 or 70 psi but it remains closed. Upon receiving the appropriate signal, the injector will open up (duration remaining open is called pulse width) and this pulse width is measured in miliseconds (ms). The SIS ECU utilizes the pulse width to set up the Gas Injection Mapping.




 Sequential Injection Technology



A Sequential Gas Injection System receives just 1 injection opening per cycle (completion from Stroke 1 to Stroke 4 in Otto-Cycle engine), timed to coincide with the opening of the inlet valve. As a very rough guide, the injector pulse widths for an engine at normal operating temperature at idle speed are around 2.5 ms for simultaneous and 3.5 ms for sequential. In doing so, SIS can eliminate engine backfire, which is a common problem with Gas Carburetion method in EFI vehicles.







SIS CNG Reducer and SIS CNG Regulator


SIS CNG Reducer is a mechanical eletronic control device that reduces CNG pressure from 200 bar to 3-5 bars while SIS CNG Regulator regulates a consistent flow of gas fuel for the engine's needs.


SIS CNG reducer functions as a pressure decompressor from the high pressure CNG at 200 bars\ 3,000psi.  The absorption of heat, taken from parts of the reducer, heated with a tap-in engine coolant, prevents freezing up on the reducer's components during the fall in pressure phase.


Picture Source: www.landirenzo.com


SIS Regulator

 Landi Renzo (Italy) SIS CNG Reducer\Regulator





Picture Source: www.autogasitalia.it 


Autogas Italia CNG Reducer

Autogas Italia (Italy) SIS CNG Reducer



SIS CNG regulator kits have built-in CNG solenoid valve, controlling CNG to flow from the regulator into the Air - CNG Mixer. (Or, it shuts off the CNG when the engine is not running or when, in the case of a bi-fuel vehicle, gasoline is selected).


Picture Source: www.autogasitalia.it  

SIS CNG Regulator 

 SIS CNG regulator and Gas Distributors to Injectors


 SIS CNG regulator kits have built-in CNG solenoid valve, controling CNG to flow from the regulator into the Air - CNG Mixer. (Or, it shuts off the CNG when the engine is not running or when, in the case of a bi-fuel vehicle, gasoline is selected).


 Picture Source: www.autogasitalia.it  


SIS CNG Reducer & Regulator

SIS CNG Reducer  &  SIS CNG Regulator  (Autogas Italia)











Manometer (Pressure Gauge) And Bi-Fuel Switch-Over


The Selector Switch is fitted at the dashboard, enabling the driver to choose either the CNG mode or the petrol mode of operation. The electronics built into this unit also ensures safety by switching off the gas solenoid whenever the engine is switched off. It also indicates the quantity of CNG available in the cylinder.


Picture Source: www.ngv.com.my


 SIS Microswitch


The wires that connect the switch to the different parts of the system must pass from the dashboard to the engine bay and should be secured by plastic ties. All connections must be made with the terminals supplied for that purpose. For SIS CNG vehicle, the Switch-over (called Microswitch) is programmable for automatic petrol (gasoline) change-over to CNG-NGV at pre-set parameters. Commonly, an EFI NGV vehicle will start-up with petrol (gasoline) and drive on for a change-over in awaiting to achieve a pre-set parameter, such as Deceleration from 2,000rpm or CNG reducer temperature achieving 49oC. The change-over will automatically take place when the pre-set parameters are achieved and they trigger the change-over automatically.








MAP Pressure Sensor  


A MAP (Manifold Absolute Pressure) sensor is one of the sensors used in an internal combustion engine's electronic control system. The manifold absolute pressure sensor provides instantaneous pressure information to the SIS ECU. This is necessary to calculate air density and determine the engine's air mass flow rate, which in turn is used to calculate the appropriate CNG flow to be injected. SIS uses MAP to calculate air mass, is using the speed-density method.


 Picture Source: www.aeb.it


MAP Sensors

 MAP and Pressure Sensors








SIS Electronic Control Unit (or SIS Microprocessor) 


The operation principle of the SIS is based on the petrol injection system where each injector works separately and independently for each other. At every moment while the engine is running, the petrol ECU’s strategy of the fuel supply is used. The gas injectors are controlled by means of the signals which control the operation of the petrol injectors, which in turn come out of the current engine need (required for power and dynamics). Aluminum enclosure and electronic elements which are working in wide range of temperatures are used to guarantee the correct operation of gas control unit and resistance to interference.



Most SIS ECUs are available in 4-, 6- and 8- channel (cylinder) version:

– 4 cylinders version, for engines with 3,4 cylinders
– 6 cylinders version, for engines with 3,4,5,6 cylinders
– 8 cylinders version, for engines with 3,4,5,6,8 cylinders




Picture Source: www.ngv.com.my




SIS ECU are commonly programmed with special interface softwares. There are types and versions that can be used to program SIS ECU. Some softwares utilitize COM2 Serial Port, while others uses USB connection on Personal Computer, particularly Notebooks or laptop. 


Some softwares require a security key (or doggle) to unlock certain programming features. Others are free to download from their website, such as Lo-gas's MACHPro in the NGV Community.com Library. As for brief comprehension, the below screen shots are meant to provide a simple and easy to understand on SIS ECU configuration. Details on Step-By-Step configuration will be omitted; nevertheless, Configuration Manuals on SIS ECU conversion kits are currently available in the library as well.       



Picture Source: www.ngv.com.my


 SIS ECU Software - 1

 Sensors Parameter Screen Shot (A Good Configuration) - Monitoring Page





In the Monitoring Page, sensor values are displayed for SIS Installer to obtain the current state of affairs with the SIS CNG-NGV kit installed on board the vehicle. The description of the values (or parameters) are as below:


(A) - The Injector Pulse Width (Injector Open Timing) on the average of 4 petrol injectors accumulated.

        The Blue horizontal bar indicates the Injector Timing for each Petrol Injector.


(B) - The Injector Pulse Width (Injector Open Timing) on the average of 4 CNG injectors accumulated.

        The Blue horizontal bar indicates the Injector Timing for each CNG Injector. 


(C) - The engine speed is displayed due to the wiring connection to the vehicle ignition coil, or distributor

        unit. RPM measurements are important to set up CNG Injection Mapping against engine speed

        and loads. 


(D) - The display indicate the temperature in the CNG Reducer, which is part of the parameter for Petrol to

        CNG automatic switchover. Pre-heating the CNG Reducer is essential to avoid poor power

        performance at the initial moments of any fuel switchover.


(E) - The display indicate the CNG Gas temperature. This paramter setup is to ensure that the flamability

        rate of CNG gas is within its limits.


(F) - This display indicates the vacuum pressure in throttle body or manifold tube.


(G) - This display indicates the air-fuel mixture through the oxygen (lambda) sensor in obtain stoichiometric






The Monitor Page can be read as the CNG Injector to open a longer pulse width of 4.18 ms than at 3.26ms on petrol injection. Since petrol having denser state in a form of liquid, the fuel mixture can be achieve with a shorter injector open timing. As for CNG, it has a lighter and less denser form in which a longer pulse width is much require to obtain a balance air-fuel mixture (as shown by the lambda sensor for a balance mixture).  Caution: This Monitor Page indicates a good or efficient SIS ECU setup that was already completed before.




The following screenshots demonstratein brief how a good or efficient SIS ECU setup is being done. All detailed technical configuration are being omitted. For indepth understanding, Configuration Manuals on SIS ECU conversion kits are available in the library under Manual Downloads sub-section.       











Most SIS ECU Interface Softwares are designed with an AUTOCALIBRATION function. A SIS Installer will only need to start-up the vehicle on petrol and leave it running for a couple of minutes. The SIS ECU will obtain parameter reading with petrol injection pattern and timing as shown in Monitoring Page (A) above. (Note: Several pre-requisite configurations have been omitted at this point)




SIS Autocalibration Function

Auto Calibration in Petrol Mode for Petrol Mapping


Upon completion of autocalibration in Petrol, a Petrol Map can be generated from the values collected by various sensors, such as MAP Sensor and Injectors. A Petrol Map can be charted up as below shown.




SIS Software Interface - 2

 Petrol Mapping after completion of SIS Autocalibration







After petrol mapping is done, the vehicle is started up on CNG mode. Again, the vehicle will be left running for a couple of minutes.  The SIS ECU will obtain parameter reading with CNG injection pattern and timing at Factory Default setting. (Note: Several pre-requisite configurations have been omitted at this point too.)



SIS Autocalibration Function

 Auto Calibration in CNG Mode for CNG Mapping




Upon completion of autocalibration in CNG mode, a CNG Map is generated from the values collected by various sensors, such as MAP Sensor and Injectors. A CNG Map can be charted up as below shown.



SIS Software Interface - 3







As below shown, the Petrol Map will form the baseline (Red Linear Line) and the CNG Map compared against it. The objective here is to match the CNG Map with the Petrol Map, in which the CNG injection will assimilate the petrol injection pattern as closely as possible.




 SIS Software Interface - 4

 CNG Map being compared against Petrol Map as the Base Line






 SIS Software Interface - 5

 CNG Injection will mimick the Petrol Injection Pattern as close as possible








Timing Advance Processor (TAP) or Advance Corrector


Timing Advance Processor can be used on all electronic ignition composed by high tension rotary distributor and a power amplifier. The timing advance processor adjusts the ignition timing when the engine is running on gas and resets the original advance (timing) when the engine operates with petrol. The timing advance processor improves performances and consumption on CNG-NGV operations.

Picture Source: www.aeb.it




Timing Advance Processor (TAP) - Joker-N for most Caburetor Vehicles












CNG - NGV Refilling Valve


Natural gas is compressed and enters the vehicle through the CNG-NGV Refilling Valve, direct into the CNG cylinder. The refilling valve must be mounted with a specially designed metal bracket, which is to be affixed to the vehicle body with bolts & nuts. The bracket of the filling valve has a hole; a part of the valve passes through it and the end is fixed with a nut. Both the bracket and the valve must be rigidly mounted to withstand the pressure of the hose nozzle every time gas is loaded. This component must not be installed near the car battery, to avoid the possibility of a spark while loading; a spark combined with gas can cause an accident. It is also advisable to place it near the regulator, so as to be able to control the filling pressure with the system manometer.


Picture Source: www.ngv.com.my

OMB Refilling Charge

 Refilling Valve and Refilling Charger (NGV-1 Standard)



A loop or Pig-Tails must be made between refilling valve and CNG reducer\regulator every time there is a change in direction of the pipe, or only one if the pipe maintains one direction. It is very important that this section be as short as possible, to avoid passing over other equipment in the engine bay.

Picture Source: www.ngv.com.my


Pig-tail Iswara 

 Pig-Tail at 90o Angles on Pipeline, Mixer, Petrol Solenoid, Voltage Stabilizer, Power Screw














Written and Presented by Dr. Xander Thong, MLVK Certified Gas Installer (Malaysia)

(If you have noticed any error or inaccuracy, kindly email and notify to drxander@ngvcommunity.com)


More Back 
Click here to send this message. Click for printable version.

Web Sponsor [Section H 3]


Advertisement [Section H 1]

Paid Advertisement



David 250size





Web Sponsor [NGV 101]

Advertisement [Section H 2]

 Paid Advertisement

Hijau Warranty Booklet 250size


 Hijau Carburetor Package 1

 Hijau Carburetor Package 2













 Yeong 250size

  Carburetor Mixer NGV Conversion

Here is My Experience!


















Mandy 250size

EFI Mixer NGV Conversion

 Here is My Experience!




















David 250size

 Sequential CNG Injection System

Here is My Experience!









Hijau Carburetor Package 1



AddThis Feed Button

Copyright © Hydrotech 2006 | Advertising | Contact Us | Best Viewed with IE 6.0&above (1024x768) | Powered By WCMS | Stats