i decided to feel how it is on boostcut. so i took of my fcd.
since it was a very cold night i thought id be boostin something higher than 8.6lbs.. and so i did. at 4k i already hit 8 lbs and as soon as i hit red line on second gear.. (whoa) it was on 10lbs.. wtf is goin on. . this is not normal. but cool.. can some one explain whats goin on.. my mod are on my sig. (nothin much to look at).

 

I'd cast a suspicious eye on the aftermarket boost gauge, especially if it has the letters A___M___R in the name. What does the factory gauge read, approx, when the aftermarket gauge reads 10psi?????

 

When you unplugged the FCD, did you plug the boost sensor plug back into the boost sensor, or did you just unplug the FCD plug from the boost sensor?

 

I had a similiar experience with my S5 turbo. I hit .8-.9 bar without an FCD. My boost gauge is an Apexi EL so I think its pretty accurate. It damn well better be for what I paid for it. Anyhow, I contributed mine to a boost spike. Needless to say I watch the gauge closely around redline now.

 

why would you wanna see what your fuel cut feels like....no offense but hit the fuel cut harms your engine...

 

Well I struck out with the autometer idea. Apexi does not spell A___M___R. Your probably right about the spike. Just wondered if your factory gauge is reading anything at all? No reading might mean the ECU isn't seeing the output of the boost/preassure sensor.

 

Nice TII....its soooo nice when there all wet

 

can i buy a vowel ...letter-U.. **** it autometer!

 

actually i found out this morning that the boost pressure line was disconnected off the sensor. no wonder i was gettin bouncin idle.. could this be the reason why i hit 10lbs..

 

i would say previous owner had ecu reprogrammed ?

 

im proly gonna start my engine replacement like in a couple of weeks. so i guess i tried to **** it up o sumthing. i d n. i do weird things when im fuct up..hhee

 

by reprograming the ecu. does that take away the fuel cut or move the limitr into a higher psi.....

 

Without FCd I wouldn't hit fuel cut to 11 psi on my S4, measured on the same line as the Map was installed on.. Hit it a couple of times, but you really had to keep in it deep to get it to cut..
FCD was added, and of course no more fuel cut..
I don't believe fuel cut harms motors.. Some people think ignition cut would be better, but remember fuel will still detonate without a spark from the plugs, so killing the ignition would not accomplish much except pump your turbo and 8 feet of exhaust pipe full of raw fuel and air, so when the ignition came back...BLAMMM.. yeah that would be safe..Max

 

Its funny that you mention that. My factory boost gauge isn't reading anything, along with my oil pressure gauge. Yet my pressure sensor and wiring are good.

Vosko makes a good point... My ECU is used Jspec (N374). Its possible that my ECU has been modified by previous Japanese owner. My EEPROM has numbered labels all over it and does not look stock.

 

the j-spec ecus are different. even if it was stock it would still have a higer fuel cut then US ones.

yes this is why you didn't hit fuel cut.

 

Can someone give a clear and concise explanation on why hitting fuel cut would damage your engine?

The way I see it fuel cut is just that - no more fuel at that moment initiated by the ecu when the boost parameters are correct to cause this. Engine is still rotating and the oil is still being injected into the rotor housing.

Determined by the ecu, fuel flow returns, engine has dropped in rpm and boost level dimished.

Where and how in this scenario does damage occur?

 

Looking at the 87 fsm, I see that the boost gauge gets its input from a spliced wire off the output of the Boost/pressure sensor, and gets its ground from the same gang of wires that ground the airflow meter, tps etc. In other word independent of anything happening inside of the gauge cluster, which includes the oil pressure gauge. Oil pressure gauge seems to be a different issue.

Looking at the 89fsm ECU outputs on www.fc3s.org, the input from the Boost/pressure sensor is pin 2H. Thats if you wanted to see if its getting there from the boost/pressure sensor. Must be though since you hit fuel cut.

I've seen posts by Ted and maybe NZCONVERTIBLE, that when you hit fuel cut, no matter how fast the fuel is cut, it will run lean for a moment. The gist of it, I think, is that the mechanics of the fuel delivery are not instant on and off. I'm am a turbo novice and it might be showing.

 

I could see it if fuel cut meant a reduction in injector pulse width, but being that its turning the injectors off completely, worries of leaning it are completley unfounded IMHO... That was the days before soft touch ignition control was incorporated into ecu's and soft touch ignition cut may still no be enough to reduce turbine speed and therefore boost, but as I said previous just cutting the ignition is a bad idea, and fuel will still detonate with out spark at high boost levels..Max

 

Ted and I discussed this a while ago after I asked the same question. I couldn't see how it caused engine damage, and I'm still not 100% sure, but Ted managed to kill an engine by bouncing it off the fuel cut, and it's hard to argue with that...

 

How is it different, just the boost cut? I m hitting just under 10 psi, with no fcd and I've never had fuel cut. I know the guy before me swapped the engine with a jspec, guess this means the ecu too.

 

"what if i put a checkvalve on the pressure sensor line..im guessin this will act as a fcd. wouldnt it.. "

 

No, a check valve only limits flow in one direction. You'd need a pressure regulating valve. This does work, but not that well. The electronic method is much better.

 

Why do you say that? AFAIK, fuel cut is at the same boost.

 

I thought a FCD is acually a bad thing to buy, because when your running higher boost you need more fuel, but the ECU is only sending the engine Enough fuel for stock boost levels. Wouldn't fuel cut off be better remideed by a Haltech ECU and largers injectors, and fuel pump? (if running high enough boost injectors and pump are needed)

Someone please clarify the details of this set-up for me.

 

of course the haltech is better. but that with injectors is $2000. the FCD is ok as long as you add enough fuel too. like a walbro fuel pump and FCD for 10-12psi. that's $200 total. slight savings.