antsz28

Ok guys maybe y'all can help me with this issue. I'm getting a bad hesitation between 2000 and 3000 rpm when I give it half throttle or more sometimes less throttle. So far I've cleaned and swapped the maf (brand new), changed coil packs (all 8 ) new tps, new upstream o2s new down stream o2s, checked fuel pressure and key on engine off is at 53 psi and bleeds off at WOT it's at 49-52 psi and at idle it's at 52 psi and new plugs. It's throwing no codes! but it does this all the time except sometimes when I gas it at a higher speed. If I get on it from a low speed or stop it'll do it every time. It's an 01 firebird formula 4.8 swap 4l60e and yes the computer still has the ls1 tune. I've done everything but changed the fuel pump and there's one one the way. Can anyone help me out? It's driving me insane. It's something simple and it's killing me. Mods that are done is full exhaust 1 7/8 long tubes and true duel system out the back.

RPM WS6

iTrader: (3)

That fuel pressure is too low (should be ~58-60psi at all times with the engine running), but not sure why that would cause a stumble in that specific rpm range only. Perhaps there are injector issues as well? Are you using the LS1 injectors or the 4.8 units?

antsz28

I'm running the ls1 injectors and fuel rail. Also it did the hesitation this morning at 80 mph so now it not just in that rpm range.

antsz28

Anyone?

RPM WS6

iTrader: (3)

Well, fuel pressure is low (unless the gauge was bad), and you said that the issue is spreading to other rpm ranges now, so perhaps fixing the fuel pump problem will take care of this.

antsz28

I've gotten the pump in today and going to install it this weekend. Put it on hp tuners and EVERY sensor is working as it should, but when it does the issue for some reason it pulls -10 degrees timing. My tuner thinks computer has gone bad. Knock sensors are working as they should and o2s are also..

RPM WS6

iTrader: (3)

What do the fuel trims look like (both ST & LT) in general, and especially when the issue is happening?