Originally posted by jshilli1
OK now I'm confused again -
The turbo sucks air through the MAF. So if my MAF is reading say, 128, and assuming the boost is at 0 (atmospheric pressure) or above, the air wants to leave the high pressure area (intake) to the low pressure area (atmosphere). So the ECM thinks its getting 128 amount of air, but some is leaking out, so the engine is getting say 100. So the ECM commands the injectors to give fuel for 128, to which the O2 replies, woah, thats too rich. So the BLM's fall off to 105. So here are the possible cases-
vac leak, pre-turbo - MAF reading is too low (high BLM)
leak, post-turbo, under boost - MAF reading is too high, since some of the air blew out (if under boost) (low BLM)
leak, post-turbo, under vacuum - MAF reading is again too low, since some air is getting in the engine that the MAF didn't see (high BLM)
so then in the exhaust, I agree, any leak will cause high BLM, because oxygen gets in the exhaust gas making the ECU think the engine is lean.