I have a cultus 2009 EFI, FF CNG. Had a variety of problems....but solved.
Problem No. 1) Sometimes it refuses to convert on CNG. (Problem started with car refusing to convert on CNG rarely and after about 1 year it started happening regularly)
Problem No. 2) Sometimes it converts to CNG but the RPM stays very low...feels like there is very low pressure.
Problem No. 3) CNG light blinking continuously, no matter what.
Problem No. 4) Not converting to CNG on its own (i.e when you are not accelerating it)
These are four main problems of this F***ing EFI Cultus with FF CNG, Now here are the solutions.
Problem No.1) After taking car to many mechanics (Diagnosing switch problem), one of the mechanics opened CNG kit/apparatus (Installed in the engine), he unscrewed some nut and oil came out of the kit (i am not talking about cylinder), then he adjusted this nut. After this never had problem No.1 and Problem No.2.
Now there are other things, which you should do to avoid these two problems, (1) In the morning, let the car's engine heat up while standing, till the time heat needle reaches center point and secondly avoid filling low pressure gas in your car. what i understand is, this oil creates blockage in that CNG apparatus and thus the supply is stopped.
For other two problems, i am still trying to find the solution, but no worries i can live with those!
Hope this helps...