Apr 14

All about CNG kit

I have come across a lot of questions from hear & there and summarized them as “All about CNG kit“.

First of all understand that most of the CNG fitment centers are manned by uneducated businessman who have no background of auto engineering or any engineering, so do not expect them to educate you with finer details of your queries. Almost all the labourers who install your kits in fitment center are uneducated people who do not even know what they are doing.
They just follow what was taught to them by the old or senior staff or learnt by themselves by experience.

So, in short I would like to to say that you have to get yourself educated about the CNG fitments and tuning, else you will be making unnecessary rounds without getting clarifications.

Before you get the CNG kit installed, you should clearly ask about the pricing, type of kits like-open loop kit, closed loop kit or sequential kit, whether bill would be given against payment, whether all parts would be imported, if not then what parts will be Indian and what imported, and whether RTO endorsement is included in the price. Also be clear about the capacity of cylinder being fitted, commonly 12 Kg or 14 Kg.

The best kits are made in Argentina and Poland. And aahh plenty of duplicates are also available in India to make things even worse they are hard to identify. Also note that after installation of the kit the fitment center will send his person with you to the gas station to fill gas for first time for setting and tuning the kit. Hear comes another as there is a racket too, the staff of fitment center will tell the gas station that the car owner does not have the metal plate that is mandatory for filing gas, and the gas filling staff will fleece you with a higher amount which will be shared by the gas station staff and the fitment center staff. bummer 🙁

You have to agree for this as you need to fill gas in your tank without metal plate.
Now the catch is “metal plate” is given free after the kit is endorsed by RTO on the RC book(in most of the places like mumbai). But for a month you will get a small paper receipt, which you can show at the gas station while filing the gas.

The average that you get after installation would be around 60% more than what you get in petrol in city driving. If car runs 10 Kms in one liter of petrol, it will run 16-18 Kms in 1 Kg of CNG if the tuning is optimum. If the setting and tuning is properly done then there will not be much power loss and no warning lights blinking. On highway, when driving the car at uniform speed of less than 50 Kms per hour you will get very good mileage, much higher than city driving.


There are safety taps in the kit to open and close gas supply from cylinder and at filling unit. The CNG kits contains a storage tank connected to a reducer to reduce gas pressure, then to mixer that feeds mixture of gas and air to the injectors. The gas and air mixture is sent to the engine where spark from spark plug burns the gas to generate pressure that moves the piston and gives power/acceleration to the car. In this simple Open Loop kit, the tuning for best performance is done by setting the gas flow, RPM of engine and spark quality. That’s all. If you master these three, you will be able to tune your open loop CNG kit of your car on your own for best performance.

One very important aspect is that never leave your car unattended while the kit is being fitted. You will notice that the CNG fitment centre will try to get rid of you by saying that he will install after few hours after finishing the existing car, etc, etc. The moment you leave the fitment centre you will be taken for a ride. I have observed that the fitment centers do not have trained personnel to install the gas tank in the boot. Instead of drilling they use fat nails and hammer the boot floor to make holes.

This not only weakens the car floor but also causes harm to your wheel alignment and other mechanisms. It is as good as impact from an accident…they hammer so badly. This is the reason many people complain that their car floors developed cracks after few months.

When the installation of tank is done, the fitment center never does the centring of the tank. Means that the tank has to be kept in such a way that the weight is distributed equally on both the sides of the center-line of the car. The tank has to be placed in such a way that it does not have more weight on either left or right side, else your car will have varied tyre erosion, and will also affect the suspension, steering system, etc. When you will turn the car in speed you will notice that on one side the car feels different than the other side. This is dangerous.

Those people who had LPG installed before switching to CNG will see plenty of big holes left after removal of LPG tank. The fitment center will not do anything about it. Most of you will not even know that such a hole exists as you were not present when the kit was being installed. If there are such holes then cut an old spoilt tyre tube, bigger than the hole size and dampen it with fevibond, leave it for at least 10 minutes and place it over the hole after cleaning the area. This can be easily done by yourself. If you wish you can get the area welded also. But for that you have to finish the gas and remove the empty tank or get it done before new cylinder is fitted.


Manual tuning can be done in open loop system. For closed loop and sequential system tuning is done through computer. You will notice that there is one big screw on the pipe that goes from reducer to mixer. This controls the amount of gas flow. There is another big screw on the reducer, which controls the RPM. These two are to be adjusted to get the best tuning.

First of all place both the screws on full open, means full unscrewed. Then ask someone to turn ignition key while you keep the accelerator on higher side. If the engine does not start, open the gas screw by 3 full turns. If engine does not start again open by 3 turns. Keep doing this till you get the engine going with accelerator pressed. Now release accelerator and keep on opening and closing the gas screw till you get fairly good engine running. Then set the RPM with the screw on the reducer for best idle.

For good mileage set the gas to lean by closing the gas screw a little, and for more power set it to rich by opening the gas screw little. Now switch on the AC. If the engine starts to stall, open the gas screw a little and then increase the RPM a little till you get good and sensitive, responsive acceleration. This will be the best setting if you wish to run your car more on AC.


There are good chances that you may see flickering engine warning light, or the light may come on and off. This indicates that your sensors are working well but the setting is defective. The defect can be in wiring, the timing advancer or loose spark plug connections. Mostly it is the power booster or timing advancer or oxygen sensor wire. So, check that first.


Everyone wants their CNG car to run similar to petrol. But there is some loss in power always. To get the best power, use NGK spark plugs, keep the spark plug gaps to lower than .9 mm. Lowering the gap of spark plug is as good as advancing the timing. Spark plugs and timing advancer/power booster play a very important role in generating power. If not set up properly, you will not get best power and acceleration.

You can slightly increase the gas and increase the RPM to get power, but the mileage will suffer, and it is not the best practice. Sometimes using larger gas mixture unit helps. At times cleaning the injectors and exhaust also helps in gaining power if they are clogged.


This is a small unit that controls the spark time of the spark plug in relation to the movement of the piston. As CNG is not as dense as petrol and requires more burning time, it is required that the spark is generated little before when the full compression reaches so that by the time the compression is to its maximum the gas is fully burnt making maximum expansion and pushing the piston with more power.

If the spark is not advanced it will not burn the full gas mixture and not generate more power and also leave some gas unburnt and you may see engine malfunction light on your dashboard. The advance timing is denoted as degrees. It really needs good experienced person to set the correct advance timing. Unluckily, most of the CNG kit fitment centers are unaware of the technicalities of advance timing.

In some original imported kits the timing advancer / power booster comes as part of the kit by default, while in some you have to buy as add on by paying extra. It costs between Rs 1, 000 to Rs 2, 500 depending on brand and quality. Cheap Chinese ones are also available.


When open loop fitment has more control over oxygen sensor and injectors, it is called closed loop. This gives little more mileage but costs about Rs 2, 000 to 4, 000 more. This setup controls the flow of gas to the injectors as advised by oxygen sensor and control unit to gain more control, giving power and saving gas to little extent.


This is a fully controlled system having plenty of sensor controllers(about 40 to 48 sensors) to control each and every move of engine, gas supply, mixing, etc. Nothing is set manually in this setup. One has to use computers to do the tuning. Once tuned, you have to never touch the settings. Your car will run as good as it was running on petrol with very little power loss.

But the cost of this system is twice as that of open loop. The problem with this setup is that in case of any defect you have to visit the specialized fitment center only. Road side mechanics will be of no help. You will not be able to do tuning by yourself unless you have the software, its knowledge, and connectivity of your engine with your laptop to do the settings.


As I already told you, almost all are no good, there is no such thing as best fitment center until you know whats going on. There are many instances where they did not give bill against cash payment after fitment saying that bill will attract 12% taxes. They brutally hammer your car for making holes and your car is bound to develop cracks after you use their services.

They even try to first place few defective parts by taking a chance that if it works, they will get rid of the defective part and make some money. Their accountant is a corrupt fellow and tries to make money by asking amounts for extension of gas filing receipts if you did not get the metal plate. The gas date extension is done free of cost (in most places) You have to just show the expired receipt and he will make new one for you in 5 minutes, free of cost.

The only way you can save your car is to be present and question them if you sense any mischief. The fitment of CNG kit does not take more than 4 hours. Most of the fitment centers will avoid your presence and will make various reasons to make you go away, but you stick there like a leech if you want to save your car from abuse or know what they are actually doing.


-The cost of open loop is Rs 24, 000 to 27, 000 without RTO work.

-The cost of closed loop will be Rs 2, 000 to 4, 000 more

-The cost of sequential kit will be between Rs 35, 000 to 50, 000.

-RTO endorsement will be Rs 2000. But if you want to get it done by yourself, the fitment center will give you all the documents and you can get it done from RTO for less than Rs 300.

You have to negotiate when deciding about the price. Be clear about tax, invoice, RTO endorsement charges, warranty, etc.


You will receive a metal plate with embossed car registration number and kit details. Sometimes, the CNG filling stations may demand you to show this metal plate before they start filing your tank. So, always be clear that the fitment center will be giving you the metal plate free of cost.

The life of CNG gas cylinder is very good, but the government has made it mandatory to get it rechecked after every 3 years and get fitness certificate from the authorized cylinder checking station. You have to carry this fitness certificate in your car in case it is required to be shown with RC endorsement. But rarely any RTO checks this.


If you feel that your car is sluggish and is not performing as per your requirement there is another way to increase power and acceleration, etc. Remove the negative terminal of car battery for half an hour, then put it back. When you will start and run the engine in CNG it will appear not to be properly tuned, but after starting the car take a ride in clear roads and accelerate to great speed, ride flyovers in high acceleration.

The car CPU that lost its memory due to disconnected battery will now learn the aggressive way of your driving, place the data in memory, and the car will run as per your driving habit on CNG.

that it….
Enjoy your ride and make sure to drive safe. 🙂

Permanent link to this article: http://zappmania.in/2016/04/14/all-about-cng-kit.htm


    • jimmy on March 30, 2017 at 9:39 am
    • Reply

    What do you think about ford figo is successful in cng sequential kit

    • derpakjoiya on May 28, 2017 at 8:40 am
    • Reply

    one of the beat article and it was really useful.
    Thank you so much

    • kalind on August 16, 2018 at 7:15 am
    • Reply

    where are you from..? I have proper knowledge and way to describe it..!
    I am from Ahmedabad. Want to convert Tiago Automatic to CNG. If you are near by (!!) I like to have conversion under your watch..!!!!!!!!!!!!

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