Need help with Fuel Cut Problems.....

[96_TSi]

1996 Talon TSi awd, t28, k&N, full 3" exhaust-straight through. car was running great at 16psi with stock catback now with catback 3" I have fuel cut problems with anything past half throttle. With the silencer in the Muffler it runs better but cuts out a little. Stock fuel system the problem?

[MKIIISUPRA]

Fuel cut is your friend :) , just be happy to know the system is working properly. When you upgraded your exhaust you more than likely increased your boost because of the improved flow characteristics. Now how to actually fix that. Several things can be done, the best option is standalone or at least piggyback.

Other ways, up the fuel pressure, upgrade the fuel pump, and/or injectors <----with bigger pump/injectors piggyback and up is a very good idea.

edit: forgot the other half of the equation, larger AFM/MAF, this will cause the ecu to 'see' less air which actually causes fuel cut

[lagos]

Fuel cut is your friend :) , just be happy to know the system is working properly. When you upgraded your exhaust you more than likely increased your boost because of the improved flow characteristics. Now how to actually fix that. Several things can be done, the best option is standalone or at least piggyback.

Other ways, up the fuel pressure, upgrade the fuel pump, and/or injectors <----with bigger pump/injectors piggyback and up is a very good idea.


None of those things have anything to do with fuel cut.
Fuel cut is a factory overboost protection that kicks in when a car goes past a certain boost level. Upgrading the fuel wouldn't eliminate fuel cut.

96_TSi, if your problem really is from fuel cut, then you should turn your boost controller down or get a fuel cut defender. Anytime you install a free flowing exhaust, your going to hit more boost and possibly boost creep in the upper rpm's.

[marshallpre1]

yep, just need to bypass the ecu to eliminate fuel cut. if you're running lean, then it MAY be due to an insufficient fuel system, clogged injectors, etc.

[MKIIISUPRA]

None of those things have anything to do with fuel cut. Fuel cut is a factory overboost protection that kicks in when a car goes past a certain boost level. Upgrading the fuel wouldn't eliminate fuel cut.

96_TSi, if your problem really is from fuel cut, then you should turn your boost controller down or get a fuel cut defender. Anytime you install a free flowing exhaust, your going to hit more boost and possibly boost creep in the upper rpm's.

:roll: you need to do some reading bud. But you're right in a way i was wrong because i forgot the other half of the equation, a larger MAF/AFM (whatever is on you car). The ecu is stupid, it does what its programmed for on STOCK parts. If you increase fuel flow, increase the air's volumetric flow rate with the same sensor (this in turn causes less air to be 'seen' by the ECU which is DIRECTLY linked to FC) you're essentially tricking the ECU

[MKIIISUPRA]

None of those things have anything to do with fuel cut.
Fuel cut is a factory overboost protection that kicks in when a car goes past a certain boost level. Upgrading the fuel wouldn't eliminate fuel cut.



here, i found this, it may help you understand things a bit better :wink:

WHAT IS FUEL CUT?
Fuel cut is actually a removal of the the injector firing signal from the ECU. This is to say that your engine computer doesn't put fuel in the engine, hence the name.

WHAT CAUSES FUEL CUT?
Despite the rumors of fuel cut being caused by too low of fuel pressure, too small of injectors, high flowing exhaust, high flowing intake, or large turbos fuel cut is not directly caused by any of these. Fuel cut is actually caused by the ECU seeing more air entering the engine than it was originally programmed to use. This likely cooresponds with an injector duty cycle which is unsafe or unattainable. So basically fuel cut is caused by the MAF seeing too much air. Don't ask what too much air is....

WHY DO WE GET FUEL CUT?
Since fuel cut is caused by the ECU seeing too much air we get fuel cut by increasing the air flow through the MAF.

WHAT CAUSES TOO MUCH AIR TO BE SEEN BY THE MAF?
Many things can cause this. basically anything you do to the engine to make more power increases the airflow...way to many to list here.

SHOULD I GET RID OF FUEL CUT?
NO NO NO NO NO...Do not use any device to eliminate fuel cut. Fuel cut is there for a reason. If you are hitting fuel cut the ECU believes that you are moving more air than the fuel system can safely deliver. If you are having to eliminate fuel cut with some sort of defender either you have an inadequate fuel system, inadequate tuning tools, or a leak somewhere.

WHY DO LEAKS CAUSE FUEL CUT?
Since fuel cut is caused by air flow and not actual AFR lost air can cause fuel cut.

SO HOW DO I PREVENT FUEL CUT?
This really isn't that hard. You have to SAFELY reduce the air the ECU sees. This means to deliver more fuel to the engine (assuming you are shooting for the right AFR) per air count. To do this you must increase the injector size (fuel flow per air count) and then use an new ECU program or AFC to decrease the air count accordingly. Not going to get into tuning now.

WHAT SHOULD I NOT DO TO PREVENT FUEL CUT?
Do not decrease air counts without adding more fuel per air count. This will cause you to just run lean all the time and cause exactly what fuel cut tries to prevent. So....
DO NOT PUT IN A FUEL CUT DEFENDER.
DO NOT RUN A 2G MAF ON A 1G WITHOUT A WAY TO BALANCE IT OUT.
DO NOT JUST LEAN OUT YOUR AFC TO UNSAFE AFRs.
DO NOT TURN DOWN YOUR GM MAFT TO UNSAFE AFRs.
DO NOT TRY AND PUT IN LARGER INJECTORS WITHOUT FUEL MANAGEMENT.
DO NOT TRY TO UP THE FUEL PRESSURE WITHOUT FUEL MANAGEMENT.

[lagos]

Thanks. I fully understand how fuel cut works.

Fuel cut is actually caused by the ECU seeing more air entering the engine than it was originally programmed to use.

aka over boost protection.

[MKIIISUPRA]

Thanks. I fully understand how fuel cut works.



aka over boost protection.

i see what you're saying, but the way it comes across when you say "its from a certain boost level" is suggesting there is a preset boost limit ie after 14PSI fuel cut comes when that obviously isn't true because 14PSI on one turbo is completely different from 14PSI on another.

Sorry if i misunderstood, its just the way i read it.

[lagos]

It depends on the car too.
Some cars do it just based on input from the mass air flow sensor (like the dsm) while others have a separate map sensor that is triggered by boost pressure. On my car, i have an AFM, and a map sensor. The AFM is used for air flow/load calculations, while the map is used for fuel cut and factory boost gauge. Factory fuel cut is set to 12psi regardless of turbo, and has to be disabled to run more boost.

[MKIIISUPRA]

It depends on the car too.
Some cars do it just based on input from the mass air flow sensor (like the dsm) while others have a separate map sensor that is triggered by boost pressure. On my car, i have an AFM, and a map sensor. The AFM is used for air flow/load calculations, while the map is used for fuel cut and factory boost gauge. Factory fuel cut is set to 12psi regardless of turbo, and has to be disabled to run more boost.

didn't realize there was a MAP on the celicas, :mad: wish i had one stock. Did toyota still really use the AFM's on the 98's??????

[96_TSi]

Thanks for the info guys. The boost controller is all the way down, its still peaking at 15-16psi. With the silencer in muffler it breaks up, sputters and shakes a little at full boost. Without the siliencer the fuel cuts out completely. Ran good at 15psi with stock cat back. Probably going to upgrade the fuel system with injectors, pump and regualtor then get it tuned; but not sure if that will be all I need. I need to do some more research....
Thanks again for the help.

[MKIIISUPRA]

Thanks for the info guys. The boost controller is all the way down, its still peaking at 15-16psi. With the silencer in muffler it breaks up, sputters and shakes a little at full boost. Without the siliencer the fuel cuts out completely. Ran good at 15psi with stock cat back. Probably going to upgrade the fuel system with injectors, pump and regualtor then get it tuned; but not sure if that will be all I need. I need to do some more research....
Thanks again for the help.


you'll need a piggyback with that stuff, and again, a larger AFM/MAF housing would be useful

[lagos]

didn't realize there was a MAP on the celicas, :mad: wish i had one stock. Did toyota still really use the AFM's on the 98's??????

94-99 celicas with the NA 5sfe motor are 100% map based.
However...
I swapped a 1990 3sgte turbo motor into my car that uses the old AFM flapper door (i ****ing hate it) to measure air flow AND has a map sensor that is only used for fuel cut reasons.

[MKIIISUPRA]

94-99 celicas with the NA 5sfe motor are 100% map based.
However...
I swapped a 1990 3sgte turbo motor into my car that uses the old AFM flapper door (i ****ing hate it) to measure air flow AND has a map sensor that is only used for fuel cut reasons.

yea, i had one of those flappers on my 3vz-fe....terrible idea.

[turbo4g63]

Put in a walbro 190 fuel pump and you should be good....thats what i'm running, just check my journal for mods

[lasthope05]

Boost creep is your main issue along with no fuel mods what-so-ever. T28's and 16g's love to boost creep at low rpms. What that and coupled with the fact that you just freed up back pressure in the exhaust system you allow the turbo to work even more effeciently.

There are several things you can do. Port you wastegate hole larger. Get an afc/logger. 16psi is perfectly fine for stock injectors and pump but if you plan to up the boost even more then you should also upgrade these parts.

[RSbeast]

Check for boost leaks!!

99% of the time it's a leaky IC line/coupler causing the 'cut' or 'bucking'

[peteyturbo]

Boost leaks will set off a fuel cut earlier, it's all about how much airflow your MAS sees versus air temp ect....I just used a VPC with GCC and couldn't be happier..Speed density in 30 min..

[Jeff822]

Check for boost leaks. I hit fuel cut a few times in my GSX and the culprate was a big boost leak. Do you have a MBC? try turning it down to like 13psi. Get some 550's, a 190 pump and an S-AFC have it tuned.

[AWDboostin]

at 16 psi I would definetly say up the fuel with everyone else,no need to upgrade the mafs though,the stock 2g maf is good for anybody that doesnt plan on breakin 450hp,and as for turning down the boost controller and still hitting 16psi,boost creep can definetly be a problem,and you wont need a new fuel pressure regulator with a 190 pump,if you get the 255 you will need the afpr

[96_TSi]

just got 680cc injevtors walboro 255, regulator and gauge planning on puttin it in soon and getting it tuned for 20psi. running 15psi now with boost contrtoller all the way down. breaks up a little at higher boost. hopefully all will go well again

[turbo4g63]

You ought to invest in DSMlink sometime soon. Hopefully your car will run ok with the injectors you are putting in. If you only have an afc or something you won't be getting the best results out of the car. With dsmlink you could set it up to run those injectors and get the most power for your money.

[TROLL]

do you know what your wastegate pressure should be? are you running higher than that, particularly at higher RPMs?
if your wastegate isnt able to keep boost at a set (lower) pressure, and it rises above the intended wastegate pressure especially at higher RPMs, then your issue is boost creep.
i know that might be basic but just trying to identify what the problem is for sure before you go about trying to fix it.

of course there could be a variety of other reasons you are having issues as well, most of which are outlined above. i'm gonna have to go with the majority though and say that a turbo upgrade on stock fuel is asking for trouble...

[BlkWhtTSI]

680ccs are fine with the safc any higher and you'll need dsmlink, get a wideband, and take it to a tuning shop. do you have the stock turbo in there now? if so the 680s are overkill for that turbo and i would put back in the stock ones.

[96_TSi]

Ive got a garret t28. Im getting a widebaned street tune which comes with chip ecu and basemap for my setup.Tuning will be done with a custom hex edit to adjust for bigger injectors and MAF flow.

[TROLL]

if you want to get down to basics, reread my post and answer the questions in there...
and also, whats factory boost cut set to on your car?

[BlkWhtTSI]

i think your setup will be fine.that turbo is a good size for those injectors (the turbo I'm getting is a lil big for these injectors but they will work). All you need is the tune. you were getting too much fuel due to the bigger size injectors the car saw that there was a excess amount of fuel and cut it off. With a tune the car will see that much fuel as normal.

[96_TSi]

Ok, but I didnt put in the injectors yet.... I assumed I was not getting enough fuel so it cut it off, and sputtered. Im not sure if the wastegate has anything to do with it or not. Im not sure what the pressure is. im putting in the pump, injectors, and regulator/gauge this weekend and making an appointment. Hopefully ill be able to give it some hell once more.