Low BLM After Up Pipe Removed

[jshilli1]

Am I correct in assuming, after I removed and put back on up-pipe the other day, now BLM's are 105, that I left something loose? I mean, vac leak before the throttle causes low BLM and vac leak after the throttle causes high BLM, right?

 

[stickybones]

I really don't want to think right now, but...

Wouldn't a vacuum leak anywhere after the MAF cause a lean condition and high BLM?

Doesn't a vacuum leak anywhere after the MAF mean the car is ingesting more air than the MAF is telling it?

Don't really see the logic in the before/after throttle body theory on the BLMs.

Mike

 

[jshilli1]

Basically if the leak is before the TB, it isn't a vacuum leak (well maybe at idle or low AF) its a boost leak - the pressure is high between the turbo and the TB so some of the air bleeds to the atmosphere instead of being pushed into the engine.

Thanks StrikeEagle I was just trying to make sure I wasn't thinking about it backwards.

 

[TurboDave]

ANY air (not accounted for) leak POST MAF (that is, after the MAF), all the way to the turbo's turbine inlet (where the O2 sensor lives), will cause high BLMs.

 

[stickybones]

jshilli1

Yeah I was just thinking about idle conditions (or as my post said...not thinking at all).

 

[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.

 

[Eric Stage I]

When you start approaching 0psi or higher, learn mode in the ECM is turned off and PE is turned on, so the BLM's will not be able to change at that point.

Regards,
Eric

 

[TurboDave]

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.

If you're refering to my post, my post deals entirely with pre turbo air. (post MAF to Pre turbo). And does not deal with any boost or even low vacuum conditions. Your BLMs can only learn during idle and normal cruise conditions. It takes very little effort to get into P/E mode (where BLM learning is disabled anyway).