System Too Lean Error Codes
 

I swapped a stock LS7 from a 2007 Corvette Z06 into my 1986 Camaro and am using the stock E38 computer that came with it. The MAF is mounted in a 4" Spectre MAF Housing.

I keep getting error codes indicating the system is too lean, and when I check the fuel trims with the live data function on my code scanner they are usually around 25%. The trims are high regardless of rpm, so I've pretty much ruled out a vacuum leak plus the system also uses a MAP which I thought would adjust for a vacuum leak anyway?

Hawks built my wire harness for me and loaded a street tune on the ECM. I'm guessing that the table they loaded was for an 89 mm diameter MAF housing so the ECM thinks it is getting less air than it really is with my 100 mm housing. In fact the difference in area between the two is 26.2%, almost exactly what my fuel trims are off.

Can anybody confirm that when using the LS7 style MAF card the tune has to be adjusted if the diameter of the MAF housing is changed? I guess the easy way to tell would be to just go insert the 89 mm tube that comes with it and see if the fuel trim problem goes away, but I'm being lazy plus I'm not sure where I put it.