RylAssassin

Ok my freind and i had this hour long argument about boost and how it is attained. The discussion came while talking about FCD's. To summerize an FCD tricks the comp into thinking that the car is only getting 6-8 pounds of boost therfore the fuel cut never engages, Is this correct? Ok now our argument was about boost levels. Ever since ive been in this forum ive heard countless of ppl saying how if you mod your exaust and raise your boost level natuarally you MUST get the FCD becuase if you hit fuel cut, there goes your engine. And my buddy RYLMONKEY made a good point that made me think for a second. If the FCD is NOT installed and you have the capability to boost past 8psi and hit fuel cut how in the hell can the car continue to create boost if there is no more fuel being added? I mean Boost can only be created through combustion is that not right? SO then is not the real reason for getting an FCD to keep fuel flowing so that MORE boost can be created? And how can you harm your engine by hitting fuel cut if basically when you hit fuel cut theres not going to be any more power? Please clarify this for us guys. Thanks sorry this is so long

Evil Aviator

There is a difference between "fuel cut" and "leaning out". The fuel cut is caused by the factory ECU which intentionally cuts the fuel to the rear rotor to keep the engine from over-boosting. The fuel cut is rather violent, and probably isn't very good for the engine over time, but at least it is better than over-boosting which can blow the engine instantly. Yes, a FCD creates a false boost signal to the stock ECU (and therefore also to the stock boost gauge) so that the engine can boost a little higher. By doing this, the engine will "lean out" because the ECU thinks that the engine needs less fuel than it really does. While leaning out is gradual as opposed to the more violent fuel cut, the lean condition will get increasingly worse with higher boost and rpm. Also, the stock fuel system was not designed to deliver any more fuel than the stock engine needed, so boosting over stock levels may exceed the max fuel flow of the system, which will also worsen the lean condition. A lean condition will generate heat, which can fry your engine if it gets to a certain point. This is why you need to upgrade your fuel system when you install an FCD.

Please read here so that you don't install an FCD thinking that your engine is "safe":
http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm

RYLMONKEY

ok this is what i was saying if u straight pipe a turbo car ull gain more horsepower then that means u will hit 8 psi sooner than normal which means fuel cut will activate sooner and as soon as that happens the car slows down rather crazy. am i right or wrong?

RYLMONKEY

also if u get a FCD and dont have a way to control the fuel. and the ecu thinks its running 8psi then it will give out 8psi worth of fuel cept ur hittin 10psi. which means less fuel more air, more likely chances of detonation! right!

RylAssassin

Thanks Evil

RylAssassin

Evil, basically what we want to know is if we do not install a FCD and have an upgraded exaust system, will the car exceed 8psi of boost?

3isacharm

evilaviator, if the stock computer thinks you're making stock boost levels, and you're running a FCD, how does the computer balance out the a/f ratio if you're over stock boost? it seems that if the computer thinks it's at stock boost, it will provide fuel for stock boost, no matter what fuel components you've put on there. i'm confused again

Edit: i think i answered myself: S-AFC

RX7withNitrous

get some kind of fuel controller either s-afc or a full ems and injectors and a fuel pump.

3isacharm

i didn't think of the fuel controller until after i'd written everything. as far as the full ems, well we wouldn't even be talking about the stock ecu and fuel cut if a standalone was involved.

Evil Aviator

Yes, you could think of it that way.

Exactly. The lean condition can also damage the engine just from the heat, depending on how hot it gets, and how long it stays hot.

It depends on the exhaust system, other modifications like high-flow air filters, how you drive the car, outside air temperature and pressure, etc. A simple catback may not overboost the engine, while a full exhaust with downpipe and no cat will most likely overboost the enigne. No matter what you do, if you drive your car like a grandma, you will never overboost.

The stock computer doesn't balance out the AFR, and that's the problem. A fuel computer like the S-AFC will modify the ECU signal to the injectors so that they can stay open longer, but then there is still the fuel starvation issue to worry about because at some point the stock fuel injectors and fuel pump will not be able to flow enough fuel.

This web site will explain how to modify your TII, and should answer a lot of your current and future questions.
http://fc3s-pro.com/sitemap.html

A full EMS with boost control (ie Haltech E11, Wolf3D 4.0, etc.) will bypass the fuel cut, completely solve the flooding problem, bypass the slow stock ECU, eliminate the 3800 rpm hesitation, allow for user-defined boost control, allow the removal of the stock AFM, allow for tuning both fuel and ignition, allow for turbo timer and rev limiting functions, and give readouts for the air/fuel ratio, boost level, and other indications. Now all that's left is to upgrade the fuel system and port the wastegate.

3isacharm

is that all?

rotary>piston

even if the comp is confused about the boost, there is still an air flow meter right? It senses the incoming air and supplies as much fuel as it can with the stock fuel pump and duty cycles on the injectors. To run 10 psi an S-AFC isn't necessary, it's just a very good idea. Some people get away with it without an S-AFC, but it's better to just get one and avoid the risk.

3isacharm

yeah but that's still an expensive risk i'd rather not take. it seems it's either save the money for a standalone, or save the money for a rebuild. i'd rather not piggyback the thing.

RETed

Boost sensor does not adjust fuel.&nbsp It only retards ignition timing.


-Ted