Actually not surprised that would help you a bit..

I also made another observation about the stock O2 sensor, it has terrible resolution, but it refreshes pretty quickly.. I wonder what its voltage correlates to AFR and if it can work to rough in stuff with Evoscan for the time being. Unfortunately with only a few 10ths of a volt to work with, it really can't be used to tune seriously..

 

Not suremyself exactly, but anyone with an Apex-i TT or the like might be able to do a bit of research on O2 reading vs. narrowband AFR.

 

O.K. so this is a shot in the dark,

Lets assume that the tune was safe and reasonable when you left the shop however long ago, then about 10 days ago something occured that caused you to start running leaner than before. Now you add back a little fuel in the problem spots and all seem well again, or at least better.

I would be looking at the fuel pump and the fuel pump pickup screen.

I had a bout with the lean condition myself, changed out the stock pump for a walbro, no love, noticed at the time the pick up screen was a little dirty, replaced that about two weeks after the fuel pump and my afr's dipped by at least .5 across the board.

Could have easily gotten some dirty gas, or stired up some crap in the bottom of the tank and clogged up your pickup filter. And from what I have seen that would be enough to lean you out by .5 across the board at wot.

 

The problem with that is that it is partially dependant on EGTs. So the narrowband voltage for, say, 11:1 will be different from car to car and sensor to sensor.

l8r)

 

Not a bad idea. Might be worth the look.

 

Alright, update time.. Kudos to those that suggested un-metered air. It seems the intake pipe connection to the MAF may not have been completely secure. We secured all connections, including that one, and the car pulls like a banchee. Didn't get the chance to get a log last night, but it's the smoothest that it's been in a while. The wideband goes on soon and then we'll be able to get some real data.

 

Yeah, that will certainly cause a lean condition and low maf reading I would think