here's the problem: I have burned out 2 catalytic converters, and my car shoots flames when I downshift. Its mostly stock, except for the motor swap, I/H/E. I am using a 89 Integra computer, and SI fuel injectors. I have recently had a new distributor put on, along with new plugs and plug wires. I pulled the plugs and they are black. I acts like it is dumping fuel, except I am still getting 30 mpg. what should I check next? I have replaced many parts chasing this problem to no avail. please help!!

 

do a leakdown and compression test.

 

...and if that's OK then get yourself to a wideband A/F meter.