I have experienced the same very problem which you are experiencing and I can guarantee that local technicians won?t be able to resolve the issue. Personally, I have changed fuel filter twice, fuel regulator, fuel pump genuine Denso and problem was still intact. They will make you change each and every equipment twice to thrice but they won?t be able to solve it. Anyway, I have gained a lot of experience in diagnosing these issues. You will have to perform number of test and specifically I have bought Air Conditioning Pressure gauge in-order diagnose fuel pressure issue. Sorry locals does not have an access to this simple device. Doing this myself is now easy for me.
Advice first: Go to manufacturers workshop and let them handle the issue. They will ask more but that would be the money well spent.
TESTS NEEDED TO RESOLVE AN ISSUE WITH FUEL LINE
Advice two: Perform these tests.
1) Get hold of Pressure gauge and measure the fuel pressure by clicking the ignition( look at your manufacturers book let for more details and right pressure readings?. If problem is diagnosed with the pressure go to fuel pump, take the wiring clip out and measure the Voltage which goes to the fuel pump. It should be equal to one you have on battery terminals at that instant. If you not found your culprit then take the fuel pump line off from pump side and take it off through engine side. Try to blow air through it either via pressure pump or try to suck it through compressor. Keep a pen and paper on hand and keep on writing the results. Let the fuel in line spills and after if air flows without any obstacle then go get hold of good pressure regulator from scrap yard, take the fuel assembly out, replace the regulator along with the fuel filter(genuine or Japanese ) and this should resolve any issue you have with fuel line and if problem still intact then get ready for a next step.
2) Goto the engine area, start the car and run it on petrol. Take the wiring clip off from every injector one by one and put it back before going onto next injector. Do the same with ignition coils once though with injectors test. If engine stalls on any injector then you have found your culprit, don?t be quick in replacing your injector, wiring should be the first to be suspected, test with OHM METER for continuity. If all ok then proceed to next step.
3) Re-verify that Advancer emulator is connected properly, wirings are done fine so that you know once spark plug timings are advanced on CNG then does it retrieves back to petrol settings once switched onto the petrol. Rest details regarding how to do it are lengthy.
4) Last of all, if your vehicle also spills patrols during refilling then problem points towards charcoal canister. Bad vacuum condition might be a culprit which does not lets your pump work properly. This issue can somehow be linked and combined with point 1. Remove the charcoal canister, its valves, clean the purge valve using carburetor cleaner. Take the canister to the tire shop and ask him to pump air fir every hole with pressure. further, you can dig on this on internet how to resolve the issue.
5) Last the least very important step and also linked with step 1. If Voltage at pump side and battery side at that instance are same but less then you need to run your vehicle on CNG. Go to the battery and measure the Voltage while Alternator is charging it. Perform the tests on Alternator through and through as at times, due to a dead diodes in alternator, it’s not producing correct Voltage. Low voltages such as 11.0 Volts, 11.5 Volts also causes issue with fuel pumps and does not let it create a pressure needed to let the vehicle run properly on petrol.
I hope, you would have understood that these steps requires some knowledge and brain so local technicians won?t be able to resolve it. If their fluke works then that?s a separate story.
