89 bronco 351 engine prob any ideas

its a 89 bronco 351 with headers but every time u push the gas down hard it loses power and back fires or just bogs down. i took it in and the guy said it was the battery. he also try to scan it and said it wouldn't work. so im thinking its the timing chain and gears but i wanted some one else to think that to. first it would have no power and would move it back fire and the rpms would go crazy and it would run really bad but i pulged the idle control sensor on the side of the intake and it helped but pushing on the gas slow it runs good but push it a little to fast no power or back firing so and ideas anythink would help thanks:cwm27:

Take the cap off the distributor and check for carbon tracks inside. If it has tracks or is cracked it will make it back fire. It almost sounds like pre-ignition. Put a bottle of cleaner in the tank and see if it improves over the next tank of gas. It sure sounds like it's all carboned up.