Fuelcuts questions

[\\\Wiktor]

When do you start getting fuel cuts om a RB25DET ?

And is cus the AFM is maxing out or is it a map sensor(if there are one?) that is working like overboost protection?

And do any one have the pin diagram for the Ecu?

thanks, Viktor

[Guest MRE]

Mine starts to stuter around 13psi.

Runing 8psi Low and 12 psi High.

Not much point going for a fuel cut if it is a stock Turbo/Ceramic as it has a good chance of falling to bits at 15psi.

[GTS-t VSPEC]

I am pretty sure that the factory boost cut(fuel cut) is around 1.1bar, the car will prevent you from boosting higher to stop damage to the turbo. In general you should have the cut left on if your using the factory ceramic turbo.

Once I had my boost controller put in then I can set the boost cut limit, therefore I think it is related to the boost solenoid/actuator rather than AFM, but that's my best guess.

If you are running a bigger turbo that can go past the factory fuel cut then I would suggest investing in either a boost controller or an aftermarket management.

See'ya:burnout:

[MYGTST]

the fuel cut happens when the computer reads 4.5v or higher from the afm usualy around 1 bar on the standard turbo

you can over ride thif function in 3 ways

method 1 : lower your boost

pros : no more fuel cut and cheap

cons : lower boost ?? not an option

method 2 : fuel cut defender. this unit tricks the computer into thinking the afm never rises abve a preset limit usualy between 4.3 to 4.45v (user adjustable)

pros :cheap $100 -$300, easy install

cons : will lean out your engine if not set up properly,

limmited use will only allow up to 4 or 5 more psi dependig on your fuel system

method 3 : new ecu

pros: yeah baby i can do anything now

cons: $$$$$$$$$$$$

currently i am usinf a fuel cut defender untill i can afford an ecu but it works well for me and i have a larger turbo than stock and am running about 14 psi(the fuel cut would come on at about 8 psi with new turbo as it moves so much more air through the afm)

works well for now and i made the fcd myself if anyone wants one let me know or pm me

[DAMQIK GTS-T]

Originally posted by MYGTST

i made the fcd myself if anyone wants one let me know or pm me

I would love to know how to make one,

A circuit diag or something would be great

Regards

DAMQIK

[Steve]

I'm with DAMQIK, the more info on these pages, the better for all - no liability for damage done of course;)

[GTS-t VSPEC]

MYGTST,

When I put a Blitz SBC boost controller in it removed/made adjustable the fuel cut, does it tap into the computer to adjust the fuel cut?

See'ya:burnout:

[whatsisname]

Another thing to keep in mind with the RB25DET ECU fuel cut.......

As the ECU uses the AFM voltage signal (anything over 4.5V) the point it cuts will vary depending on air temp & density. A modified RB25DET still using the stock ECU may well hit the FC @ 8-10psi on a cool night, yet it'll run 10-12psi on a mild/warm day without a hitch.

[Steve]

EDIT: sorry if this is drifting off the original theme of the thread:

Whatsismane,

Would this mean that if you tune your car on a hot day, on a cold day as the air is alot denser it could throw out the air fuel ratio and cause detonation?

Steve

[MYGTST]

Originally posted by DAMQIK GTS-T

I would love to know how to make one,

A circuit diag or something would be great

Regards

DAMQIK

im not keen on handing out cct diagrams as i spent a lot of time developing this cct and fine tuning it to be better than the brand name ones which still fuel cut every now and again.

but i will make them and sell them to whomever wants on just let me know it costs me about $65 in components im asking for $80 ea for them. i think that its a reasonable price for my time

ill also give wiring and setup instructions( or do it for you )

i currently have on setup in my car so if you want a demo let me know

[\\\Wiktor]

Thanks guys!!

Now i know

[inark]

why not just get ur ECU remapped/reprogrammed? or can u not do this with R33s?

which gets rid of all the fuel/speed/boost cuts or whatever... mine cost me like 300 and with the ECU remapped to work better with my setup it runs better

[whatsisname]

Originally posted by Steve

EDIT: sorry if this is drifting off the original theme of the thread:

Whatsismane,

Would this mean that if you tune your car on a hot day, on a cold day as the air is alot denser it could throw out the air fuel ratio and cause detonation?

Steve

Steve,

No mate. The ECU is still aware of exactly how much air is entering the engine regardless of temp & density. The AFM will register the cool denser air (via the increased voltage signal) & ensure the fuel requirements are met to maintain the programmed A/FR.

[Jay95R33]

A bit of a story to this one, so bare with me.

I've got a late 1995 GTS-t.

A while ago I blew the tacho output on my ECU (do'h).

I used the blown ECU for a few months, and while it was in I got a big FMIC. All was sweeeeet

I since got a second hand ECU and put that in. Tacho works well now but it feels like I'm hitting a fuel cut of some kind around 5000rpm.

It doesn't stop, but it does slow down heaps (acceleration).

I compared the ECU's and it looks like my original one has a different firmware installed (a later number is stamped on the main ECU).

Soooooo, is it possible that different year ECU's had different maps? or better refined maps or fuel cuts???

[whatsisname]

G'day J,

I'm guessing it's time to welcome you to the RB25DET ECU timing retard! Once the airflow goes above the AFM voltage range it pulls lots of timing to keep everything nice & safe. It just so happens that the nice denser air your FMIC is allowing has caused the above to happen.

I'm also guessing that once your AFM voltage drops drop back into its normal operating range (retard timing - less power & less airflow) that the car comes on strong again. This is because ECU has advanced timing once again (probably ~6000rpm).

The more air through the AFM the worse this will get. I had 3 big ECU commanded timing retard dips in my power curve @ the 225rwkw mark. These can be felt as huge flat spots, & seen as brief 15-30rwkw drops on a dyno run.

Having said (written) all this sometimes there's freak ECU's that don't seem to retard timing!? Bugalug's car is one of these! Like your's J, Bug's is a 95 model too.

Options to get around this issue are just the same as MYGTST listed to avoid the fuel cut:

Programmable ECU

Z32 AFM & remap - not easily done on the 33

Fuel cut defender - "can be" dodgy/dangerous

Turn down boost - yeah right!

Do nothing - & drive a car that feels like someone keeps pulling the handbrake on & off!

Why doesn't the timing retard & boost/fuel cut occur @ the same time? Buggered if I know? Anyone???

[MYGTST]

the timing retard happens when the ecu senses higher knock values which is at the engines peak tourque about 4500rpm-5500rpm the afm voltage may not have yet reached the fuel cut limit

i noticed this went away after i put in a bigger turbo as the air charge was cooler and it didnt knock anymore at the same boost level as the standard turbo

you can stop thisfrom happening by trurning your timing back a degree or two with the cas (side effect a bit less power) but much safer then detonation

[predator]

The more air through the AFM the worse this will get. I had 3 big ECU commanded timing retard dips in my power curve @ the 225rwkw mark. These can be felt as huge flat spots, & seen as brief 15-30rwkw drops on a dyno run.

Ahhh..that is what it is on mine most likely! Few times when i really stomp it there is like a flat spot where it seems like its missing or something but its only sometimes and with 100% THR (and its not the rev limiter as its before then). Seems to depend on the outside temp though as it doesn't happen that frequently.

[Jay95R33]

G'day Matt,

Thanks for the info Looks like my next mod will be a PFC and a Z32 AFM....... I'll try and get the old ECU working again. I opened it up and found a burnt resistor and a transistor that got so hot it unslodered itself from the board !!! Replaced the resistor and put the transistor back in the right spot but I'm a bit worries about putting it back in the car incase it blows something else !!!

You had 3 !!! dips in power. Wow, I bet your standard ECU was crapping itself !!!

Predator666 - yepp, that's excatly what mine is doing I thought it might have been the plugs were crapping out, but nope, it's gunna cost me more than a set of plugs......

J

[DAMQIK GTS-T]

Hey Guys/Girls

I have found this simple circuit that makes a fuel cut Defender

Try this at own risk!

I'm yet to build one myself but will be doing so shortly

Regards

Damqik

(Damqik i have remived the link here because if anyone uses this

curcuit they will dammage their engine i have already tried this curcuit and it leans the engine out big time)

(MARCIN)

[Cubes]

So what does this fuel cut actually feel like ppls (On a R32)? Motor Just goes dead?