Well I have had this on going problem for a few and I still can't get to the bottom of it.

Here is the symptom:

It's a hesitation/surge at partial throttle and low boost. But it ONLY happens at partial throttle and low boost (1-7psi). If it is at 0psi or lower I get no problems 10-20psi I get nothing. If I slam it to the floor everything works 100%.

Here is what I have checked or replaced:

Coil pack (new)
Spark plugs (new)
Wires (new)
Unhooked the Crane ignition (problem still there)
Fuel filter (new)
Air filter (new)
Wastegate vacuum lines (new)
TPS (new)
IAC (new)
DFI map (good and working right)
Crane map (good and working right)
Stock map (new) (also unhooked it and drove w/o it and the problem was still there)
Run through many tanks of gas
DFI (working fine, also pulled out some fuel in the TPS enrichment screen)
Fuel pumps (working loud and clear)
Timing is good
No vacuum leaks

I have absolutely no clue what is going on. I have done about everything I can think of for both the fuel side and the ignition side and the problem still exist. So...I'm thinking it's something else. What in the hell would cause this kind of problem out side of fuel and ignition systems?

TIA
Brian

It is a long shot but try replacing your ECU. Sounds like you changed almost everything on the damn car!

when the car hesitates, do you hear a pop, or does your BOV go off at all? What are your plugs gapped at?

Nope, no pop sound and the BOV doesn't open. The turbo just spools up link normal.

The car drives perfectly fine in normal cursing conditions (no boost) as well as WOT, pulls like a bitch and still scares the shit out of me sometimes.

It’s just a partial throttle, low boost surge and it happens every time.

Plugs are gapped at .034 and have always been at that gap even before I had this problem.

It isn’t a setting w/ the DFI because I still have everything set like it was before I had this problem. I did try playing w/ the settings but the problem still shows its face.

The ecu is fine and it is only controlling the spark not the fuel (DFI does the fuel). As far as I can see (because everything is new) the ignition side if fine. I data logged it and I get no codes and the spark advance looks 100%.

I have no clue...

Thanks
Brian

My car does the EXACT same thing, but I just figured it had too much fuel at that point, because my digital a/f gauge goes to 1.0+V when that happens.

I was thinking it may be too much fuel so I pulled a TON of pulse width out and I still have the problem I also lowered the throttle position enrichment. I had a perfectly running stage 4 for about a year and a half and I never changed the fuel map. So I don't know why too much fuel then wouldn't affect things but does now?

Brian

To a certain extent, I have the same problem. I believe it's the 625cc's. It's really not a good idea to decrease the injector pulses too much at those points where the hesitation occurs. I've tried to play with different settings and couldn't really smooth out the transition and low boost accelerations. Lowering pulses too much will only cause more hesitation problems from insufficient fuel delivery and/or injector spray patterns.

I don't think there's really any way to truly get that "stock" acceleration feel without the hesitation just because of the bigger injectors. Other fuel setup options would be the 8-injector setup or Greddy E-manage.

Well after dealing with the same problem with my 95 (here we go again with the 95's!!) I asked around and most of the general feedback I got from people, especially those with domestics like the Mustangs, say that u may wanna check the alternator. Something about the voltage output to all your accessories and crap. So, like an idiot, I'm gonna say, check your alternator and/or get a higher amp alternator for all your goodies you got. I don't really know if it'll work cuz my car still out of commission. It did the drive and stop thing too and also at highway speeds died off and kick back on. ECU read as a misfire. But I do have ecu light so I'm not quite sure it's my ecu. But now when i turn the key, I get fuel pump priming but no starter turn. Got new battery, new ecu, new starter. Thus leads me to believe I got a bad ground that's draining everything. Car battery dies in less than 2 weeks. And people said that they think it's my Alternator. Just a thought folks!

i don't know if this is really related, and i'm not stage IV, but i do know that when going from vacuum to low boost, often the ECU will keep the mixture quite lean and then it will start cycling the A/F back and forth. of course, eventually it will decide to keep it in the rich and then all of a sudden you get a surge of power. i talked to my FC3S friend, and he said "your ECU is in closed loop when in boost? that's ludicrist!" i'm working on a way right now to force the ECU into open-loop mode once boost goes above a certian pre-set level. i'm going to try 0 psi for starters.