I recently had a catless Buschur turboback, AEM intake, and SAFCII installed without a boost controller. I noticed on the road that the boost was spiking to around 22-23 PSI at 3-4 grand in 3rd-5th gears.

Now, as it gotten colder in the past two days, the engine feels like it's cutting out completely for a few split seconds and completely stuttering (In 3rd-5th) when I'm at WOT near 3-4 grand where I'm seeing 20+ PSI spikes. This is fuel cut, correct? I'm not getting any knock (According to the SAFC-II) and I'm making sure that I need a boost controller as I just ordered a Profec B Spec II. This should correct this fuel cut issue, correct?

At first I thought I was having ignition issues but I'm not having the problem in first in second where it only spikes to about 19-20 PSI.

Thanks.

 

This is fuel cut. I am experiencing this myself with an TB,intake, and piping. I have a profec e-01 and emanage to solve the problem. You shoud have a CEL here that will code overboosting.

 

Yeah, I threw a CEL but I figured it was the catless exhaust. Thanks alot for your input.

 

So how well are everyone's boost controllers fighting fuel cut?

I was told that the small internal wastegate of the stock Evo will still have problems fighting boost spikes even with a boost controller if you add a 3" downpipe.

 

Unfortunately the boost controller does nothing to "Fight fuel cut" other than regulating boost.. a Manual boost controller is basically a bleed valve, and when its set at a certain point, it will always bleed at the same rate.. so spikes will still exist if their due to the flow rate of the wastegate size, however in most cases, spikes are due to faster spoolup and the solenoid or MBC not able to bleed off the excess boost in a manner that will stop the spiking (an MBC will help minimize it, but it periodically needs to be adjusted depending on the weather)

an Electronic boost controller in closed loop mode can be used to regulate spiking because it can use a non-linear bleed, that is, if the engine gets closer to the max boost setting, the solenoid can bleed off more boost to force the actuator to open at the right pressure therefore always maintaining the correct boost level at the settings you've programmed..

There are two types of electronic boost controllers.. Some are open loop, and some are closed loop.. open loop will always maintain the setting you give it, and it can bleed boost off based on a "curve", that is, its bleedoff is not linear like an MBC so spiking can be "tuned out of it" using its gain adjustment. In closed loop, the solenoid and its bleedoff is controlled by a calculated value of RPM/TPS or other load values to regulate spiking, and other boost demons..


With all that said, fuel cut can only be controlled by manipulating the ECU into raising it, either by reprogramming the ECU, or using an AirFlow Converter, in our case, stock cars run rich, so leaning it out will effectively raise thef uel cut slightly. Upgrading the Injectors and fuel pump will also allow you to raise your fuel cut because the larger injectors would need to be tuned with an S-AFC (or similar) and therefore raises fuel cut higher because the ECU thinks there's even less load (the S-AFC adjustment is required to lower the duty cycle of the aftermarket injectors to get the same or leaner mixtures.. of course this is all done within reason since there is only so much adjustability available)

Most of the fuel tuning has very little impact on closed loop ECU operation since the car will always attempt to maintain a 'perfect stoich ratio' (usually the factory ECU goes from closed loop to open loop map operation at about 30% Throttle)

Hope this info helps.. Anyone feel free to refine or correct what I've said so there's no misinformation..

 

Jack,

Do you think the Greddy Profec B Spec II will be able to regulate boost better than the factory unit?

I'm seeing 22-23 PSI unregulated in 3rd-5th gear at around 3000 RPMs and that's when it cuts the fuel. I do believe this additional boost (And trust me, it ramps up to 20+ PSI VERY quickly compared to stock) is what is causing the ECU to cut the fuel, correct? Otherwise, I'm fine at WOT all through the powerband in 1st and 2nd.

I do have an SAFC and it was dynotuned, for what it's worth.

 

In short.. Yes, it has a gain adjustment which will allow you to set a base boost, and a bleed curve, so you can reduce or eliminate it under most driving conditions.. You may still see slight spiking when you downshift and punch it under load (that is forcing spoolup under load at lower RPM's) but you can adjust for that.

An upgraded exhaust system (especially a downpipe) definitely lowers the spoolup RPM slightly, plus spool rate.. so its no surprise to see that high a boost triggering fuel cut.. IT makes sense that its not happening in first and second, because when your accelerating, at a lower gear, the engine can ingest the additional air that would otherwise be indicated as overboost.. at part throttle, under load, the engine isn't revving as quickly, so the boost builds up faster than the boost solenoid can bleed off the pressure to open the actuator at the right time.. Hence spike..

 

I appreciate your insight. I'll be sure to keep everyone updated. I'm going to try and hold boost at around 18 PSI.

Some fuel cut is acceptable but, right now, if I punch it in 4th it literally bounces off of fuel cut as I watch the boost gauge bounce to 20, drop off, then rocket back up to 20, drop off, as the ECU tries to regulate the boost.

I'm hoping it'll at least offer me nothing more than a small "hiccup" rather than what I'm getting now.

 

if anything running a boost controller will increase your fuel cut if you up the boost. from what i have seen when you had a full exhaust your boost goes up naturally, i use to hit fuel cut so hard i felt like i was going to fly out of my car.

however i had my limit raised, so i don't hit it anymore and i'm running 22 lbs to redline

 

Yeah.. at higher boost levels with raised fuel cut, the things you end up watching is the ability for the fuel system to supply adequate fuel to maintain a safe mixture.. Thats why Injector and pump upgrades are recommended.. Personally I'm seeing duty cycles with the stock injectors as high as 95% even with 19.5psi of boost.. thats bad, and I need to upgrade the fuel system before I go any further.

 

I'm trying to lower my boost slightly, especially right near the initial spool-up at 3 grand. It's honestly all over the place up until redline as well.

I'll probably have fuel cut removed whenever Al comes back to Agile.

 

As long as your in the threshold of what the ECU sees as normal (18psi with a periodic 19.5 or 20psi spike) you wont experience fuel cut. So your goal is reasonable..

Actually your car will perform better with fuel tuning at 18psi through redline, than running higher boost with unpredictable spiking, so your definitely on the right track.

 

at higher boost you definately want different fuel pump i have a walbro 255

 

FWIW I'm still researching my options for fuel management.. I currently fun an S-AFC and an S-AVCR for boost management.. But I'm looking at other options that will also allow timing control (Not as critical as I once thought though) in addition to boost/fuel control.. After I make my final decision on a piggyback (or replacement ECU) then I'll decide if a flash is necessary to eliminate the restrictions in the stock ECU so I can control them manually. (RPM limiter, speed cap, fuel cut, etc..)

 

I'm well aware. I'm probably going to hold off on a fuel pump and injectors until the Spring when I add 264 cams and possibly a FMIC.

As I'm tuned right now, we were seeing boost levels between 17-19 PSI to redline depending on the run and having no knock. According to my SAFC, I'm not seeing any knock on the road so I'm hoping my fuel system will continue to hold up through the cold winter.