Honda City I Vtech AT: petr level reduces according to distance even on CNG

Two months back I have got CNG kit installed in Honda City I Vtech AT. Since day one petrol level reduces automatically according to the distance travelled, even while running on CNG. I visited the dealer and explained the problem, on which he changed the emulator, post which I drove 10 KM and fuel level was back to normal, but again from next day onwards it started reducing automatically.

I visited Honda service centre as well, where supervisor explained me that in Honda I Vtech if fuel is empty and yellow fuel indication is on then ECU memory resets automatically, hence for fuel gauge to read normally re-fuel the car three times for same quantity, once done ECU will start working normally. I tried that as well but didn't worked.

Can anyone advise me what should be corrective course of action to resolve this problem.

This is a common isssue that arises due to improper installation/bad quality of parts. The emulator is supposed to swtich the fuel pump off and cut fuel supply to the injectors, without the knowledge of the ECU. But in your case, its not doing its job properly, or your installer didnt get hold of the right connections to be made. Hence, petrol is being consumed by the car along with CNG. Get it checked once again. 

The fuel gauge can vary by small amounts everytime but surely, if the tank gets empty, petrol is obviously being consumed.

What? CNG and petrol being burnt simultaneously?? Does the car feel super-powerful in CNG mode?? I mean if it has both fuels at the same time, it is bound to produce more power (and even greater emissions).

Pranay, are you sure there's no petrol leakage anywhere?

Actually, it may not produce more power, but the engine will run a rich air-fuel mixture. Also, when the mixture gets rich, ECU again starts reducing fuel supply to the engine where fuel = petrol, as it doesnt have control over CNG flow. This problem has been reported by many car owners after CNG/LPG conversion and it is the result of a bad job done by the installer.

EDIT: Start the car on CNG, then shut the cng supply valve manually and see what happens.

I have done that test and am sure petrol is not consumed while on gas.

So when run on gas petrol gauge level reduces, and then when again re-fuel it, the gauge comes back to original level plus the re-fueled petrol.

@Sankalp - if the fuel mix is rich, surely there will be some interval where the car feels a bit more powerful.

@Pranay, I guess what is happening in your car is that in CNG mode the fuel gauge is getting disconnected from the fuel sending unit (in the petrol tank). This causes the gauge to by default go towards empty (it is both by design as well as fail-safe).

Try this: Once you have driven the car in CNG mode, switch off, change to petrol mode and the just turn on the battery (position where battery sign, oil level sign light up). See if the fuel gauge starts to rise (it will rise somewhat slowly or sluggishly, so be patient). If it does, there probably is no problem at all.

Sure thing Rohit, I will try that. Thanks for the advise. I hope this should work. Problem is if I am driving the car then I know the Petrol level in tank, whereas if someone else in the family will drive it they don't the actual petrol position, it is misleading.

Cheers!

Hi Rohit! I tried doing that but didn't worked. Any other solution?

Ok, so in CNG mode petrol level goes down and does not return to normal.

Next is to drive in purely petrol mode and see of the fuel gauge shows normal fuel usage. If here you see that fuel level reduces faster than usual, the problem may be in the fuel level sending unit. If this is fine then go to next step.

After this check if the same behaviour (of the fuel gauge) repeats in CNG mode. If yes then probably petrol is being used up too - this can be ascertained only by disconnecting the fuel pipe that connects to the injector feed and in CNG mode switch on the battery (but not ignition). If petrol gushes out then there surely is petrol being burnt in CNG mode (as Sankalp had pointed out). This points to an installation problem - especially relating to the fuel pump.

Hi Rohit,

Which kit did u installed? I have heard cng kits dont work well in honda and the engine lasts for only 80k kms.