Dear Xulifqar and others,
Old steps taken:
Fuel pump changed brand new Denso Japan Original, fuel filter changed brand new original, fuel pressure regulator changed after buying a second hand Kabli and Fuel injector cleaned by myself. Applying a little pressure on Fuel injectors after removing, running STP fuel injector cleaner through it through some pressure while giving the proper voltage to the injector, at-lest I could see some sound fuel pattern from injectors.
Symptoms: Hard starting and no power while starting in first 10 minutes on petrol and after that everything is ok. Everything works perfectly well, once vehicle is brought onto the CNG immediately after start.
Wiring Verifications and few TESTS.
I went further into diagnosing the issue, back Car seat was removed and gained access to Fuel pump assembly. Both the fuel sending pipes and fuel recovery pipes were removed from the vehicles fuel assembly.
TEST 1:
Took a compressor and applied suction from return pipe using Air Conditioning professional Vacuum machine. This lines goes to the engine area and returns back through return pipe. I could not see the fuel sending pipe showing any signs of taking any air. Air should have normally flown from sending pipe and returned from suction pipe. This was my assumption but did not happen like this.
Test 2:
In order to verify the wirings, connected a pipe to fuel pump assembly?s ?sending hose? and then into a collecting JUG. Wiring to the fuel pump was not removed.
Followings Is the ignition positions: Lock, ACC, On, start
1) Once ignition was moved to ?ON?, then nothing happened.
2) Once ignition was moved to ?start? from ?ON? position then Petrol started coming from pressure into the collecting jar.
3) I verified the pressure using by putting my thumb on the pipe and petrol starting spraying all over. Pressure from the pump seemed fine.
4) Disconnect everything.
5) Fuel pressure was relieved using the proper procedure.
6) This time sending unit was connected with the sending pipe, and return pipe was put into the collecting Jar. Ignition was brought back to the on position, from there to ?start? . I was able to turn on the vehicle, fuel was moving from the fuel tank into the engine but return pipe did not showed any sign of Petrol coming back. Vehicle was kept in on position for around 10 minutes but did not see the petrol coming back from the return pipe
7) Vehicle was brought back onto CNG, petrol was going into through the sending unit but again nothing came out from the return pipe.
Wirings seems to be fine but I have my doubts as petrol is not returning back from the return pipe. I don?t know how to further diagnose the issue or look for a blockage if there is any or I may be wrong completely. Looking forward to your comments.
Below are few pictures of the tests done by my self with assistance from my servant.
P.S: no signs of leakage observed from around injector area.
