Ive got a problem i just cant figure out how to fix my problem soo im turning to you all, i have a built Ls (b18b je 8.5:1, crower rods,pnp head,crower springs n retainers) It was all runnin fine until i put the motor back in, now it seems to sputter or hesitate around 4k and 5k rpm it feels like it gets no fuel and it seems to do it the worst in 1st gear, 2nd and 3rd dont feel as bad but they do stutter a lil. (fuel system consists of a supra pump, 8an fuel lines ,SX filter and regulater, AEM fuel rail, RC 310's and vortech fmu). Now the things i did when i took the motor out is i put a new head gasket, ARP head studs and a Skunk intake manifold. I took off the skunk manifold put the stock one on and it still did it, i redid the timming to make sure it wasnt a timming thing, and no still the problem was there. Now this is what the gauges read when im driving it, when i hit 4k in first gear it stutters hesitats and the A/f gauge goes to Lean, but the fuel pressure gauge is reading pressure and if i keep it floored itll eventually pick up again. If someone knows what it is it would be soooo helpfull thank you very much. If u need any more info about anything , just go ahead and ask. thanks again

 

Ditch that fuel pump and get a Bosch inline. those pumps can't put out the high enough pressure that you need with the FMU. Just stick a Bosch pump inline and it will probably fix your problems.

 

but if it goes back to being fine (not lean)then i would think that the pumpis fine.at 4k you won't be building that much boost 4psi or so then you should be fine because my stock pump does good up to about 6 psi or so. just my 2 cents

 

Since your running AN lines get a Paxton pump or an SX Pump.