I have a 1988 d 100 with a 318 that wont start I have fuel pressure and spark but here the problem when I first turn on the key it shoots a squirt of fuel into the carb but then nothing while cranking the engine so while I had some one crank the engine I poured gas down the carb then about 10-15 seconds later fuel came out the jets and it ran perfectly until I shut it off I then (with the truck running) unplugged the wires that go into the carb and it quit plugged back in and it will start from the key in the run position but not if I turn the key completely off I did the same unplugging the throttle position sensor with the same results hope I explained my problem thankful to anyone who can help could it possibly be a bad o2 sensor?