Big fuel trim swing only on bank 2

[ward360]

I am Working on a 1999 LS1 Corvette The Motor specs are as follows Stock Bottom end, AFR Heads 205cc Street heads, A Lingnefelter Cam Duration @ .050 207 / 220 Valve lift .573 / 580, and A Magna Charger with 4psi of Boost.
The problem I am having is at light throttle (regular driving) in 1st and 2nd there is a dip in power at 1800 rpm, at free rev there is a surge there too, Only at 1800 RPM.
I am including two Pictures. The first one is free rev at 2200 rpm where everything looks good to me, it is the same at any rpm besides 1800. The second is at 1800 RPM where you can see on bank 2 the short term FT has to make large changes to switch to O2 from rich to lean, Bank one looks normal. I also noticed when it does this is only when it all 100% all the way up to temp. The fuel LT trim also even bank 1 to bank 2 all the time except at the magic 1800 RPM where Bank 2 differs from bank 1 by about 10%.
This is a return less fuel system with the inlet on bank 1, If that makes a difference. I also looked into the proportional fueling tables and made sure they matched bank 1 to 2, Which they do.
Anyone seen anything like this Before or have any suggestion.

Thanks
Ward

[ward360]

Sweet no responses in 24 hours, Do I have a good one or is everyone speechless? Or am I just an Idiot. Need more info? Let me know.

[WS6FirebirdTA00]

or just give it more time for people to respond, you are not an idiot lol

Put a WB in it and see what it shows. To me, it looks like poor o2 switching is causing over correction.

[Frost]

It's that 18-1900 RPM "spot" that all of the maggies have (and yes, passenger side if memory serves). It's related to the lower intake design from what I understand; you just have to work around it. This is less of a tuning issue and more of a design problem.

[WS6FirebirdTA00]

Oh yeah, Doug mentioned this a while back.

[ward360]

Yea the wide band says it is doing exactly what it shows huge swing, on bank 2 way rich to way lean, it takes a huge pulse width change to make a difference then it makes a big switch, It act like a long throw toggle switch, (but I need a short throw) but only at that certain RPM 1800. I would throw an O2 at it but, It works great everywhere else.
Fuel Boiling in the bank 2 rail? feed is on the drivers side rail and rund under the front of the blower to the passenger side rail, no crossover in the back of the rail.
One thing I have run into on return less systems is fuel system harmonics, that cause strange lean spots that you can't program around. (I usually check those by putting on my fuel pressure gauge with a long rubber hose and seeing if it changes any, Or if you can feel any pulses in the hose.(this didn't) . Vacuum is steady. ????
Unfortunately I am the third one to have the pleasure of working on this car 1 shop built it and attempted to tune, the second shop attempted to tune it, and got 490hp out of it and now it's my turn to fix all the drive ability problems, LOL, the story of my life.... Runs good everywhere except 1800 at light throttle....

[ward360]

Sweet That is what I wanted to hear, I had that strange feeling that it was something mechanical, Just couldn't figure out what It could be...
I have only tuned 3 cars now with HP tuners now so I am still finding my way through it a little (alot), I have done plenty of others, AEM, Accell, holley, you name it. I do think I like HP better, you guys just need to get it working on all the other manufacturers too...
Thanks!!!

[Frost]

I try and go SD, get the VE as close as possible, and only re-enable STFTs if going back to CL.