Fast90 Woes - Leanness

[TAQuickness]

Mostly a rant, but I'm open to y'alls opinions/suggestions.

This is a long outstanding problem of mine. Have a fast 90 and inconsistant AFR's between banks. Running a dual wideband setup, left and right bank in the primary O2 locations. I'm 99.999999999999999999999999999% sure this is a hardware problem. To date, here's what I've tried:

Swapped injectors from bank to bank, no change

Replaced injectors, no change

Swapped injectors again, no change

Found two exhuast leaks, fixed them, no change

Tightened intake manifold, no change

Double checked vacuum lines, no problems here

Found crack in #7 runner, JB weld, no change

Crack on #7 turned into broken chunk, replaced lower shell, made new gasket, slight improvement. From here, the left bank would run 2 points higher under 2k RPM. Above 2k RPM, both banks tracked within 0.5 AFR

Remade gasket, Right bank now running leaner than left

Tightened right side of manifold, right bank = commanded, left is off by 1 - 1.5 AFR

Tightened left side manifold, shit hits fan, both banks lean, left ~ 15.5:1, right, ~ 20:1

I'm not sure what's left to try.

[joecar]

Mate, that's gotta drive a person insane...

Sanity check using stock manifold (if you're feeling up to removing it yet again...)...?

[Black02SS]

Have you swaped WB Locations?

[TAQuickness]

crazy? insane? all of the above? yes! I've RR'd the manifold some 20 times in the last 2 months. I'm sure it's in the manifold becuase the leanness changes slightly each time.

Chad - thanks for the reminder. I've also tried:

swap right to left - no change
both WB's on right - AFR's within .05
Both WB on left - AFR's within .05
20 pt WB calibration - AFR's within 1 - went back to stock LC1 config
All new port gaskets (OEM & Comp)
New x2 upper/lower gasket per write up supplied by Arkay (found on LS1 tech)

Have not tried an OEM manifold. Sold them (LS1 and LS6) when I picked up the FAST. Anyone have a stocker I could borrow?

I'm seriously thinking to try that blingy PP manifold in the near future.

[Bruce Melton]

I know many disagree but I think FAST manifolds just suck (or suck where they are not meant to). I could never get my brand new one to seat properly and it kept losening up even with locktite. In the end I cracked the LS6 valley cover which I learned is not unusual. This says that the manifold was bottoming out. It could be that the FAST gaskets are thicker than GM?
I gave up and went back to LS6/Shaner with no problems.

[TAQuickness]

I know many disagree but I think FAST manifolds just suck (or suck where they are not meant to). I could never get my brand new one to seat properly and it kept losening up even with locktite. In the end I cracked the LS6 valley cover which I learned is not unusual. This says that the manifold was bottoming out. It could be that the FAST gaskets are thicker than GM?
I gave up and went back to LS6/Shaner with no problems.

I'm feeling much the same.

[redhardsupra]

yup, i also agree. they flow great, but damn, could you please make them out of a different material than my cheerios bowl?

[caver]

I Have seen them bottoming out on the valley cover bolt heads.

[TAQuickness]

I Have seen them bottoming out on the valley cover bolt heads.

Can you elaborate on this vision? I'm using the flat valley cover bolts supplied with the manifold, but I won't rule it out till I can.

[joecar]

Pics...?