I have an 1989 TBI and it is backfiring thru the TBI. There are no vacuum leaks and the cap, rotor, wires, and plugs are brand new. The base timing is set at 6 degrees TDC. Does anyone knew what could be causing the backfiring? The plugs are one step colder then stock. I only notice the backfiring when the engine gets warm so I suspect that backfiring is caused by to much heat but I am not sure, I have never had this problem before.

Did this start happening right after you put the new cap and rotor in?

If so it could be that the cap you have is cracked and throwing sparks thoroughout the cap causing a misfire.

Did you make shure you got the cap down all the way on the dist?

Trace your wires to make shure you have the right wire going to the right terminal. You could have your wires crossed. causing a misfire.

and make shure your timing is set correct with the EST wire disconnected.

may also want to relash all your valves. My camaro used to backfire all the time... relashed the valves and it's ran good since.

Recheck the timing. Check the condition of all the plug wires, make sure there are no cracks.

Make sure the the wires go to the correct plug location, i bet you have it off 180 degrees or so!