i've just bought 91 ef with great running motor (zc) and have codes 4, 6, and 8, coming up on computer. i think i know what the 8 is but i'm not sure if it's the same when you swap the engine?? it runs good until warm then stumbles and dies. usually it restarts no problem. the computer is pm6? does that sound right? when i got the car the computer was not bolted down, it was just laying on the studs. so i guess my question is does it need to be bolted to run right or does it matter>? thanks, chip