poping/ backfiring

88 astro 4.3 i have replaced the distributor ( pickup coil was going bad) distributor cap and rotor coil and module rebuilt the EfI and new fuel injectors. i replaced a bad vacuum line and the map sensor that was sending a code for high voltage. i also replaced the throttle position sensor.i still have a pop / backfire though the throttle body when i punch it from a red light and sometimes when i am driving . would this be the timing? i moved and did not bring all my tools with me yet and can not find a timing light with anyone i know in this new town. jax fl. i did set it the best i could using a vacuum gage and my ear.anyone have any ideas i am at a loses to get it to stop pop/ backfiring.and feel like i am :banghead::banghead: and getting no were with this.

also did new plugs and checked all wires and a new fuel filter when i did the tune up. have set the timing with a light i was only 4 degrees off. also changed the fuel pump.i tested the knock sensor last night and it was not working i have a extra module pack for it so i swapped it out and got no change so i am going to get a knock sensor and replace the one in the block next.thanks for all your help on this web page. it is nice to know who i can ask for advice when i have a question.