Need help figuring out STFT bank difference

[fbody83]

I recently removed my upgraded returnless fuel system and installed a fore level 3 return style system. It consists of a -8 AN feed and return with two separate lines going to the rails (dead head setup). I tune the car myself so I made the necessary adjustments in the tune for the return style system and it fired right up.

The car idles and drives fine (while in vacuum) however, once I start approaching 0 in/hg of vacuum and getting into boost, my short term fuel trims show one bank going 10% lean and the other 15% rich. That's a 25% which is pretty big. When the car idles, and when in vacuum, the trims agree with each other. Usually this indicates some sort of vacuum or boost leak but I would think if that was the case then my fuel trims would be off all of the time?

Also, as I continue to accelerate and get deeper into boost, this problem clears up and the car pulls hard making full boost. My other thoughts is that there is a possible fuel flow issue to one side of the rails. I don't know how this would happening with my setup but I guess it could be possible. To confirm this, I'm going to swap the fuel lines to the rails and see if the problem switches banks.

Any other thoughts on what this might be? Could a vacuum leak still cause this issue? I did have the blower off to install new fuel rails.

 

[SVT GI]

Could be a bad O2, car runs in closed loop up to WOT. Put the car in open loop constant and see if it helps. Or swap O2 bank to bank and see if problem changes sides.

 

[Tractionless1]

What regulator are you using? What is your fuel pressure doing? I had a DX regulator dropping 7psi from vac. to WOT, before recovering.

 

[fbody83]

Could be a bad O2, car runs in closed loop up to WOT. Put the car in open loop constant and see if it helps. Or swap O2 bank to bank and see if problem changes sides.

Thanks, I ran the car in open loop and it still had issues getting into boost.

What regulator are yo using? What is your fuel pressure doing? I had a DX regulator dropping 7psi from vac. to WOT, before recovering.

I'm running a fore f4i. Pressure drop across the injectors is staying within 3 psi of what I have it set at.

Also, this problem seems to get worse the hotter it is. Maybe something is causing my fuel to heat up? I have the regulator in the fender but my fuel filter (which is under the passenger side door) is still hot to the touch.

 

[cj428mach]

It doesn't explain your STFT issues but when I went from regular return to dead head my tune was way off in the middle of the MAF curve and required a retune.

Also I ran my fuel setup similar to the way you are but I still had decent fuel pressure fluctuation as read from the FRPS, the cure was a front crossover.

 

[fbody83]

It doesn't explain your STFT issues but when I went from regular return to dead head my tune was way off in the middle of the MAF curve and required a retune.

Also I ran my fuel setup similar to the way you are but I still had decent fuel pressure fluctuation as read from the FRPS, the cure was a front crossover.

Thanks I'll have to look into doing this! Right now I have two separate lines going to the back of each rail. I'll take the plugs out of the front of the rails and connect them to each other to see if it helps.

 

[fbody83]

Also how many 90 degree bends/fittings do you guys have in your fuel setup? I have a few extras due to my regulator being in the fender. My regulator also makes a "wooshing" noise when the fuel is flowing. Does anyone elses do this?

 

[fbody83]

It doesn't explain your STFT issues but when I went from regular return to dead head my tune was way off in the middle of the MAF curve and required a retune.

Also I ran my fuel setup similar to the way you are but I still had decent fuel pressure fluctuation as read from the FRPS, the cure was a front crossover.

Dude... I love you and so does my car because I was ready to start it on fire. I can't believe it but the rail crossover cured this problem. Prior to doing this I swapped the lines going from the regulator to the rails thinking if it was a fuel issue the problem would switch banks but it didn't. I decided to try putting a crossover line on and bam, problem solved. I don't know why this worked but the car is running like a dream now! Thanks!!