mods are 3" TB exhaust, SAFCII tuned with a WB to low 11s AFR
(only taking out between 4% & 10% from 5200-7000) and MBC set to 1.4bar in 4th gear.

While crusing in 5th gear at 3,000 rpm when I smash the throttle it hits fuel cut real fast. I thought it was just because 5th gear would always spike higher then other gears but even with 100 oct. in the tank (94/104mix) when I roll into the throttle in 4th gear at like 5,000 rpm the car will hit fuel cut as soon as the boost gets close 1.4bar. Is that normal?

I read posts from people running 22 psi on pump gas, I'm not even able to run that on 100oct with race gas without hitting fuel cut.

 

This is a different form of fuel cut, and I don't really know what to call it, but it happens when you roll into boost in a high gear from low rpm. The boost spikes really hard and when you hit peak torque with the boost too high, it cuts out. This happens to me in 6th when my boost is set too high and I try to accelerate from very low rpm. It's not normal fuel cut, which usually happens when you surpass a certain air flow, but rather a boost cut when spiking too high. I'm not sure what triggers it, but it might be caused by too much boost while being lean at peak torque when the timing bottoms out. Hopefully, someone knows the details of this and can explain it in technical terms.

 

The OE ECU has a programed boost cut at around 22psi. The best way to defeat this is with a reflash. BTW, I'm of the opinion that you're leaving way too much torque on the table by using an AFC alone (no way to adjust timing=torque). I say go with a Turbo Trix through the mail flash, and that will fix your boost cut, set your rev limit, and allow you to keep your AFC to fine tune the fuel curve.

 

Usually it will happen just before or right when I'm at 1.4bar on my stock boost gauge which only equals ~ 20psi. But how does the stock ECU know my boost pressure if I'm using a MBC?

Warr: I thought basically the same thing as you just said but this is happening to me in 4th gear above 5k. If I'm not mistaken our TP peak is below that.
I'm an 04 but don't the 05's hit 1.4bar (20.3psi) peak boost around 3,500 rpm or so? If I tryed to roll into boost that low in the RPM it would cut out for sure...

 

i had this problem too. my mods were:RNR gt35r,hks272's,dynoflashed ecu with the s afc, 780cc inj with other supporting mods. no one can explain it to me too.
the only thing that cured it was the aem ems.

 

If its FUEL CUT that is being hit - a Dyno Flash will eliminate the fuel cut 100%

There are other conditions e.g. misfore for one which can create similar conditions

usually experience will tell you which condition you are having

 

boost cut....you run more boost in your top gear and you run most of it at around 3200rpms....

if you stomp it there, and the weather is a bit cooler than when you set your boost controller, you will hit boost cut.

get a flash to get rid of the boost cut.

 

yeah, u have to get some sort of flashed. No ifs ands or but's.

 

car doesn't feel like it is missing anywhere in the RPM range. So far I have tried the stock Iridum plugs and some NGK in the same heat range (forgot the part#) but neither fixed the problem. If it was a miss I think it would see it higher up in the RPM band and it wouldn't be sudden loss in power like this is.

It has got to be fuel cut I just don't know why its happening.
I set my boost in 4th (sometimes 5th) because I do a lot of highway driving and want to avoid spiking to high in 5th as much as possible. But the thing that gets me is my boost is only set at 1.4bar in 4th gear and I have 100oct in the tank. Thats only 20.3psi... I "should" be ok with 93 oct at that level.

 

I don't know, man. I run 23-24psi at the track when I toss in race gas, and I have never once hit "boost cut" or "fuel cut" in such a way (above 5000rpm). I only hit it in 6th gear when I roll into boost from very low rpm.

Zeus (pardon my error), you're right about the torque left on the table with just an S-AFC (not that you need to be told that). I will be getting a base flash from Al next week just for those reasons (7800 rev limit and mid-range timing for better torque).

 

First, it was Zeus who said that....

Second, 05 fuel cut is a bit higher, its like 23.5psi for atleast 2 seconds. I hit it many-a-times before i got the flash to get rid of it....and i was running 21psi in 4th...but on the hwy in 5th, id hit it everytime.

 

I hear ya. I've only ever hit boost cut on the street rolling into the throttle. And it used to only happen in 5th gear between 3-4k, now its happening even higher up in the RPM and in 4th which makes no sense at all.

At the track I can't seem to get over 1.4 bar (thats just a spike) no matter how much I crank the MBC. But I think that has to do with the engine not being under as much load as when you mash the gas on the street.

 

Funny...I didn't even look over at the name. I just saw the avatar and red GURU letters in my peripheral vision and just assume (yeah, ***, etc.), but it's now fixed.

Interesting on the 04/05 fuel cut differences. I still have yet to hit it on my 05, but then again, I don't think I've run more than 23-24psi. I've only run it that high at the track, which means I've only hit that boost above 5500rpm while drag racing...never a slow roll-on that causes a higher spike.

 

I just had the same problem this morning -- i don't know if the cooler air had any issues with it. But I was in 5th gear putting along around 3k -- dropped it into 4th and stood on it to pass someone and not 2 seconds later I hit fuel cut. I'm running about 25 lbs -- but like the others said, if I roll into boost at lower rpm I seem to it it...but if i'm at higer rpm's I hardly hit it -- I think the flash is the only way around it. Now the stock ECU is cutting fuel to maintain safe conditions...with the removal of fuel cut and we hit these conditions again that would normally cause fuel cut -- could this cause any potential problems with the engine?

 

^^^thats my question. i hit the highest boost in 3rd though. i only hit fuel cut on 8 gal of 100 and 4 gal of 93 and 23-24psi. i also only hit it in 3rd at around 5500. im just worried that if i don't have that cut i might get early detonation and loose a lot of money for a couple of whp.