Well I have already gone through all this drama and have successfully got myself through it so I will tell you what things I did to my car. But the first question here is that HOW OFTEN YOU DRIVE YOUR CAR ON PETROL WHEN CNG IS AVAILABLE? What I suspect is that some time back you drove your car on CNG while petrol in the tank was too low that caused the fuel pump to overheat and started to weaken. Since my car was almost 1 lac kms driven at that time so I think most things I did donot apply in your case. I am listing the things I did to my car
1 Changed its injector as the they were well clogged and the desi method of cleaning did not help only one was throughing petrol adequately one was completely blocked and other 2 were just very less firing. My mechanic tried to clean them using carb cleaner but to no avail. So changed them with kabli. Although ultrasonic cleaning is also available but they cost 3000rs I think for 4 injectors. The kabli ones are easily available for 3200 rs complete set of 4. But I think in your case the injectors might not be the culprit. But still you can try to test them. I tell you what my mechanic did. He took out all the injectors and then connected them all with injector cables. The plugs and cables were also taken out. He put a card board and he told his helper to try to start the car upon each self the injectors fired. Now we saw the sprays on the cardboard all the sprays were equal so that way we checked the injectors.
Second thing he did was he checked the advancer+emulator now it also had some IC malfunction so he repaired it.
Third thing he did was cleared all the error codes, according to him as there was blockage in the injectors so it has also caused problem backwards.
The fuel pump was checked for malfunction but its pressure was enough so he put it back but cleaned the fuel pump sock.
After all this had been done, the car which previously hardly started on petrol was going till 138 km/hr in 4th gear and 145 in 5th gear. It is to be noted that I had never taken the car to that speed before so I thought all is well. But one thing I did experience is that a month later after all this I took my car on m-2 it was on CNG and I was in 3 rd gear the car went till 120 and was going further but I changed the gear to 4 th. The same day while I was going I took the car in 3rd gear on Petrol and it maxed out at 110 km/hr, so I thought that may be the low fuel in the tank caused that the fuel was below half. This all was done in december, things were I went to karachi by road in march and on return I again faced the problem, 100kms before lahore on few bridges the car would take jerks and struggle to move at that time I used to down shift and use the suction of engine to draw fuel. It was cng holiday so since multan I was on petrol. 30 kms away from lahore I was stuck in traffic jam and the car suddenly shut off. I tried to restart but it did not. On third attempt it started and after that I tried to keep the rpms above 2000 even on idle so that the engine continues drawing petrol. Reached home safely and parked the car for 2-3 days. after that took the car for Ac service the car was still on petrol. When the ac service was done the car would not start.
At that time called the nearby electrician and he said that fuel pump is gone. He was an anari so messed up a lot and changed the pump but the problem persisted although the problem was not with pump this time, I had also changed the filter box. Went to the same who did all the above operation and the problem was solved but he did a mistake he used the new filter box which apparently had slight misallignment issues.
Again after 2 months the problem persisted but this time changed the new filter box with old genuine one and the problem is no more.
Since that I have made a trip to karachi 2 to islo and half of all of them have been on petrol. Also driving these days on petrol and no problem. On my last trip red lined the car on 3rd gear and crossed 145km/hr in 4th.
Now in your case there are 3 things which might be causing the problem
1 Faulty emulator. Try another emulator and the problems might go away. Actually the emulator is wirred with all injectors, TPS, MAF or MAP so if there is IC failure the car wont perform well on petrol.
2 Weak fuel pump. The problem I experienced going through all this is that in pakistan no one has fuel pressure tester except 3s dealers. The fuel pumps condition can only be verified through fuel pressure tester.
3 Error code. Go for ecu scanning and remove all errors
4 It might be a problem that your fuel is not proper. May be you filled it from a pump who had contaminated stuff.
Apart from all this I see that you are in lahore. My cell no is 0321-4047704. Call me if I can be of any further help