Does this sound right? I had my BLMs pretty good from last years tuning efforts, around 124-132, which aint too bad for a MAF car, so I called it good. But over the winter, pulled the pump, plugged off the manifold ports, and removed most of the tubing. My first 2 scans showed a general trend of all BLMs below 128, like 118-128, but avg like 120.

I read something about the air pump only puts air into the manifolds during open-loop, and then closed loop to the cat. So the ECM don't really care what the air pump is doing?

I guess I need to pull out my manuals and do some more reading, plus make some more scans.

My thinking is that I had my BLMs good last year, made no chip changes, now after pump removal, blms went down.

Any ideas?

 

It would seem that is shouldn't have changed.
Unless the diverter was stuck open in the wrong direction, but that would have added air, and shown slightly lean so removing that should have skewed things to the rich side.

In playing with an evacupan and pump I don't recall seeing more then a few points change in BLs.

 

I guess I need to make some more data scans, to really draw a solid conclusion. I still have the winter (old) gas in my tank!!

I just checked out my GM shop manual, to see what they said about air pump operation. As you know, there are 3 ways the control valve can direct air from the pump. The manifold tubes, the converter, and to the ambient air.

My manual says air goes to the manifolds in "cold mode".

Air goes to converter in "warm mode"

Air goes to the ambient in "divert mode" But then in a later paragraph says air gets diverted by:

Rich operation (read PE mode)
Problem mode when ECM fires SES light.
Deceleration
High RPM

It doesn't really spell out the actual temps that determine these modes, maybe someone else knows this.

Kind of indicates to me that air would only get sent to the manifolds or maybe the cat in open loop mode, and not in closed loop or PE mode.

So I could safely say that removing the air pump SHOULD NOT affect closed loop part-throttle fuel tuning?