89 GTA 5.7 deleted cats, installed 3" magnaflow catback, ever since then it has been throwing codes. dont have the numbers but the shop who put the catback in said it was a lean code and said that the computer needs to adjust itself to the increased exhaust flow and it will go away. He also said to clear the codes via the battery because its obd1 but doesnt that ruin the purpose of the computer adjusting after a few drive cycles? This somewhat makes sense to me, old cats were smashed inwards and muffler took a dump and it had no codes since i bought it, threw on the exhaust and there it is.

i also cut the air tube off ( will be removing smog pump etc.) later in the week

bump, does anyone know?

From just an exhaust it won't throw lean codes. The fact that you cut the air tube off however does explain it if you didn't plug it properly, air will be drawn into the exhaust and the sensor will pick up on it, OR there's an exhaust leak upstream of the sensor. Check that. The signal needs to be way lean to throw a code.

hmmm, i was told to leave the air tube unplugged as it needs to escape somewhere, i cut it off just before the cats were. but i understand what you are saying, because the rest of the air system is intact, smog pump, air tubes @ manifolds etc. if i plug it though, will it cause other issues. wont be until next week i delete the entire AIR system and plug the manifolds... and there isnt any exhaust leaks...confusing, i dont understand the mechanics of the AIR system at all really..