Okay, I have searched for this problem, and it seems that others have had this problem. Unfortunately under every post they describe their problem, plenty of people chip in advice, but no one ever says, "yup, that fixed it", or "that didn't help, this is what did it..."
See my point?

My problem is that I get under boost fine, but when I try and open the throttle up past around 40% I get a lot of sputtering. Fuel pressure comes up fine, air/fuel ratio seems to be okay, but I keep getting the sputtering. I have a custom FCD which I can see working with my S-AFC II. I can see that manifold pressure never goes positive according to the MAP sensor... Anyhow, what the heck causes this? And if you are one of the people that has had this problem, what fixed yours?

Thanks for the help!

You may have already done this, but I would start by replacing plugs and wires. It sounds like it is ignition related, although have you verified that your FCD actually works? I would also check for boost leaks.

none of that helped...

Its the simplist thing but it does affect your ignition system: Be sure your grounds are good going to the block and make sure your battery voltage stays above 12 volts. Like I said, simple yet it will definitely cause sputtering under load.

I posted this before im thinking its a ground when my car did the same exact thing, thats what it was.

I will give that a shot... so is it a ground or not grounded good enough?

I can check voltage with my S-AFC II if that starts getting irratic, maybe that is it..

So what if voltage stays above 12v?

It's more than likely a bad connection at one of the ground straps which would cause such a thing (if it is indeed the culprit). Just unbolt any large ground you can find going to your engine, and the one from the battery and make sure you are getting a really good metal-to-metal contact and everything is tight. The most important item that you want to have good voltage is the coilpack, so if you could test the voltage on the harness there, that'd be helpful to know.

If its well above 12v, its something else.

If the car is started, it should be well above 12v. More like 13.5-14v.

Originally posted by totaleclipse_05
If the car is started, it should be well above 12v. More like 13.5-14v.

It can very well be above 12 volts before he starts it but once a load is put on wiring it will cause a great deal of resistance (on a bad connection) and you will see a voltage drop across the connection which is bad. The starter cicuit can very well be getting the full voltage potential but the ignition system can see a voltage drop seperately.

How is your FCD wired in with your SAFC?

What is your fuel setup, and how much boost are you running, on what turbo?

What kind of spark plugs are you using? and what is the heat range also the gap as well. I have this problem when I run higher boost and it spikes to 25psi. It is flash-over for me that causes the sputtering look for dark like on the plugs indicating that the spark is arcing down (or up) the plug insulator. A smaller gap will help this problem I use NGK BKR7E (dont get the BKR7E-11 they have a larger gap from the factory) and gap to .030", I may need to go to .028" though. Hope this helps narrow down your problem. And does it still build boost and stutter or does it not build boost?

thanks for the help, gunna try this stuff, and let you know how it goes.