Some fuel questions.

[nicklmort]

Right now im running a td04 with a mbc at 11psi. (spikes at 13 but doesnt hold long enough to hit fuel cut) Tuned with Apexi Neo Piggyback. Fuel system is completely stock.

There are some situations where it does hit fuel cut.. cruising in 4th or 5th and get on it enough to build boost it hits fuel cut. and at about 115 it hits fuel cut.

What is causeing it to hit fuel cut? i have read that you want to have injectors to flow twice as many cc as the power your making? the car made 143 awhp at its current setup so i was thinking maybe the stock maf sensor is maxing out and causing the issues.

would it benifit me any to just get a jecs maf and a retune at current boost?

or should i do 550cc side feeds a jecs and maybe 15psi? if i did this would i need a higher flowing fuel pump?

if i wanted to do the 550s a jecs, fuel pump and 15psi would i need some sort of fuel cut defender along with the piggyback?

Thanks, Nick

[Legacy777]

You're hitting fuel cut because of boost levels. That's it. In the higher gears, 4th & 5th, there is more load on the engine. As a result boost will be higher. This is one of the draw backs with a MBC.

To keep from hitting fuel cut, you either need to get a fuel cut defender or lower the boost with the MBC so you don't hit fuel cut in higher gears.

[cj91legss]

So would an Electronic Boost Controller automatically adjust so he wouldn't hit fuel cut?

[Legacy777]

Yes, most electronic boost controllers can be setup closed loop which monitor boost and hold boost at a desired level. Wastegate duty % will be vary slightly in the different gears.

[impreza_GC8]

Same thing is happening with me, fuel cut in the higher load gears. Its simply due to the MBC not being able to hold it. If you are still using stock injectors I would think about upgrading perhaps, but that is unrelated to your fuel cut issue. I ran my VF8 with 440cc injectors at 11psi, it would cut in 5th gear because I would spike nearly 15psi.

[Legacy777]

... Its simply due to the MBC not being able to hold it.

I think this statement is a little misleading. The MBC is doing what it's supposed to do based on a given input load. The engine load is what is varying and causing the overboost situation.

Honestly, you're best option is a fuel cut defender that raises the fuel cut limit. That way it's still there to act as a safety, but shouldn't affect normal driving.

[nicklmort]

Ok, so i understand whatever i di i am going to need a fuel cut defender. But stock fuel cut is there for a reason, that reason being the stock fuel system is near static at fuel cut.

So that being said i should get bigger injectors right? does anyone know what boost levels on the td04 and 550s the stock fuel pump maxes out? And at what point does the stock maf max out?

[cj91legss]

there have been topics about having the 550 injectors on stock ecu, some have been able to get away with it and soe have not. Some just wont even do it on stock ECU. 550s will run real rich.

[nicklmort]

I have em if you didn't see that.

[Legacy777]

Ok, so i understand whatever i di i am going to need a fuel cut defender. But stock fuel cut is there for a reason, that reason being the stock fuel system is near static at fuel cut.

So that being said i should get bigger injectors right? does anyone know what boost levels on the td04 and 550s the stock fuel pump maxes out? And at what point does the stock maf max out?

Fuel cut does not necessarily mean the injectors are going static. Fuel cut is based on pressure. Fuel flow requirements are based on the mass of air entering the engine to maintain the correct AFR's. A larger turbo will flow more air and therefore put more air through an engine which could cause the injectors to max out sooner compared to a smaller turbo.

Really....what you need to do is get a WB and see what your AFR's are doing. Once you have that info, you can see if bumping the fuel cut up a few psi will affect the AFR's. If you see the AFR's are steady than it shouldn't matter. If you see them going lean or you see them drop very rich (ie going static) you may want to look at the other mods you were talking about.

Probably the best setup would be the JECS MAF, 550 injectors, and walbro fuel pump. Those mods along with the proper EM to control it should give you plenty of flexibility and scalability.

[93forestpearl]

One thing to keep in mind is where you are sourcing your boost signal from. A boost source from the intake riser will cause your sensor to read fluctuations that are much higher than your boost pressure. I had spikes that were 90 KPa higher than what was read in the plenum.