Fuel Cut: What is it? How do I fix it? [merged]

[Slanted J]

All fuel cut threads are combined here.

I've tried doing a search but to no avail.

I was just wondering what Fuel Cut is. I've heard it tossed around alot, but do not actually know the details behind it. And, naturally, I can gather that its when the fuel is cut off, but when and why.


Thanx,
Jon

 

[gsxtacy]

I am most definatly holding 12 psi to about 5500 to 6500 then I shift. My bov leaks boost over that anyway. I have not yet seen a spike in the boost and I have test driven the car about 5 times. I had my brother ride w/ me (he owns a gsx) and he thinks it is definatly fuel cut. I am running an AC TECHNIC aftermarket boost guage. It seems to be working fine.....I Idle w/ just a hair under 20psi of vaccumm and I boost up to 12 psi every time which i am told is pretty normal for the T-25.

Another thing worth noting is I have an air/fuel meter (its a piece of crap that I wouldn't trust) but when The fuel cut happens it totally dumps into the lean side and then dosen't register anything for a second. Something else that might be worth noting about my a/f is that at idle it circulates back and forth between lean and rich (normal) but it also circulates a lot during cruising speeds between rich and lean. I was told that it should read in the stoich area very solidly during cruising....could this be a clue?

 

[13secGST]

No...the A/F gauge is supposed to cycle like that at idle and at cruising speeds...whoever told you that it was supposed to stay stoich was wrong. Your O2 sensor does just this...it varies the voltage to the computer many times a second which overall achieves a very stoich A/F ratio however the gauge reads of the O2 voltage which is varing.

now...if you are sure you are hitting fuel cut...then maybe somehow lots of air is getting passed the MAS and not getting to the engine because it all leaks out the BOV...you should replace the BOV and the UICP then see what your PSI is at...it'll probably be much higher than 12. I still don't see how a T25 could flow enough air to fuel cut...I used to run 18psi in 60-70 degree weather and never fuel cut with it.

Conditions in New Mexico From Tuesday until Saturday:
Albuquerque- lows 31,33,36,36,37 highs 57,58,58,56,57
Santa Fe - lows 23,24,29,30,39 highs 52,54,56,52,54
Roswell - lows 35,37,38,38,39 highs 70,70,66,64,62
I have Satelite TV with weather forcasts all over the country.

I could have looked at more cities...but maybe with your higher boost pressure, colder temperatures, and bigger intake you are flowing more air and acutally boosting more(due to colder temps) and the BCS can't lower the boost because it thinks that it is at 12psi and it can't really lower it much more than that since the wastegate actuator is around 11-11.5psi. I bet that if you got a BOV, UICP, and MBC you would get fuel cut anymore cause you would be able to control the boost better.

But I STILL don't see how the T25 is flowing enough air to hit fuel cut...but that up there is my best explanation...as for the spark plug explanation...well I guess you could try it...it shouldn't cost more than 10 bucks...but I don't see how that is the problem unless you have bad plugs.

 

[Airpoppoff]

Originally posted by 13secGST



But I STILL don't see how the T25 is flowing enough air to hit fuel cut...but that up there is my best explanation...as for the spark plug explanation...well I guess you could try it...it shouldn't cost more than 10 bucks...but I don't see how that is the problem unless you have bad plugs.

I dont either, Fuel cut has eveyrthing to do with air flow, just remind yourself of that (gsxtasy)

Who is your freind thats telling you your hitting fuel cut, what exactly does the car do?

 

[gsxtacy]

It feels like I left the tranny back down the road a way!!...! Actually It like a whole lotta whoa......the car will be building boost fine...it usually happens at about 4to 5 grand in 2nd gear(sometimes I make it to third) at about 12psi. It has sputtered once but most of the time it feels like the turbo just quits boosting and I am running only the 4g63....I am 99.9% sure it is fuel cut(its the 1% that scares me)....I have experienced the dirty fuel filter and spark plug problems and it is nothing like that.

What about the screw on the bottom of the mas air flow unit housing. I was told to back it out till it is flush w/the housing would this help?

 

[bigjangin]

check for boost leaks, that could be causing your problems

 

[13secGST]

Are you 100% POSITIVE that your turbo is a T25 and not a T28 or BigT28. There is no reason for you to be getting fuel cut otherwise...You don't even have an exhaust yet. My first experience of fuel cut was not until I had

3" Cat-back
2.5" testpipe
K&N FIPK
MBC at 15psi
Walbro 255
VP FMIC
Greddy TypeS BOV
and Ported/Clipped Big 16g

It wasn't until I had a Big16g at 15psi.

Before that I had my T25 pushing 18psi on the stock IC and I never once hit fuel cut...not even on a nice cold 50 degree night.

I don't know what to do with that screw on the MAS will do...I have never touched mine. You have a very wierd problem. But honestly...try getting control over your boost with a new BOV, probably going to need a UICP at the same time, and an MBC...that way you wont leak boost and you will have acurate control over it.

 

[irjoshy]

i had a problem simliar to this.. i changed my plugs and my car ran fine... damn jerks before me put champions in it

 

[gsxtacy]

OK guys i REread my previous posts and realized that I wrote I have a uicp and 1g bov(I haven't had time to install these yet).... IS THIS THE PROBLEM....MY STOCK UICP AND STOCK BOV ARE LEAKING TOO MUCH BOOST OR NOT FLOWING ENOUGH AIR FOR MY OTHER MODS????????

Here is my justification...my air filter and turbo inlet pipe are flowing more air than stock through the MAS but my upper ic pipe is still that stock plastic restrictive thing and also my stock bov is leaking what little air/boost is flowing....CAUSING A BACKUP OF BOOST THUS FUEL CUTTING MY ENGINE...CORRECT ME IF IM WRONG!!??

 

[Prodigy]

if u are running stock bov then it is not likely for u to hit fuel cut..due to the stock bov not holding boost....sounds like spark plug wire problem to me..

 

[13secGST]

Originally posted by gsxtacy
Here is my justification...my air filter and turbo inlet pipe are flowing more air than stock through the MAS but my upper ic pipe is still that stock plastic restrictive thing and also my stock bov is leaking what little air/boost is flowing....CAUSING A BACKUP OF BOOST THUS FUEL CUTTING MY ENGINE...CORRECT ME IF IM WRONG!!??

Originally posted by 13secGST now...if you are sure you are hitting fuel cut...then maybe somehow lots of air is getting passed the MAS and not getting to the engine because it all leaks out the BOV...you should replace the BOV and the UICP then see what your PSI is at...it'll probably be much higher than 12. I still don't see how a T25 could flow enough air to fuel cut...

Originally posted by 13secGST Are you 100% POSITIVE that your turbo is a T25 and not a T28 or BigT28.

That is what I was trying to tell you...and also you didn't answer my above question. But these other people are also saying that it could be you spark plugs...I've never experienced the spark plug problem...so I don't know if that is not it.

 

[gsxtacy]

The plugs I am running are NGK-R bpre6's (or something like that) and they are gapped @ .030.

Magnecore 8mm wires.

It is possible that the fuel filter under the battery is clogged and once I reach 12psi and a heavy load that the fuel solenoid sees a drop in fuel pressure and cuts the fuel completely to save the engine.

That is what fuel cut is for right??? to save the engine.

Like I said my brother has been into DSM's pretty heavy since 2000', and he swears it feels like FC.

My UICP and 1g BOV will be installed in the next few days whenever I get a chance, I am so busy with work and family.

Once the UICP and BOV are installed if the problem persists, I will move on to spark plugs, wires, and then fuel filter.

It doesn't throw a CEL at all after this problem. Does Fuel Cut cause a CEL??

I appreciate all your valuable input.

thanks

GSXTACY

 

[bigjangin]

do you have a boost gauge? Can you give a detailed description of what happens?

Ive experienced 3 different things. Fuel cut and when I had a boost leak were very similar. The car would be pulling under boost, then BAM it feels like I hit a brick wall. With fuel cut the car would stop going and it was in the higher rpm ranges(this was on a car with an 18g). When I had a boost leak it still felt like hitting a brick wall, but it happened in the lower rpm ranges and the car would still pull.

A misfire which I also had feels like your car is hesitating, or stumbling over itself. The more throttle you give it the more it hesitates. Hope this might help.

I suggest doing regular maintenance(fuel filter, plugs and wires) and checking for boost leaks with an intake leak tester.

 

[ElusiveGSX]

I installed 550ccs on my 98 gsx and now with the type s bov dumping normal back into the intake the car jumps and hesitates around 4 or5k rpms is this Fuel cut what do i need besides an safc (which is on the way).And also the car runs fine when the bov is dumping in the air and the hole for the dump tube past the maf is left open ,what could running it this way damage?

 

[13secGST]

yeh...do the UICP and BOV to see how much boost the turbo is actually trying to produce...also, one question...does your car do this in all atmospheric conditions? or only really when it is cold? And does your boost drop off at redline...like does it drop to around 10psi?

Last...you still haven't answered if you are 100% POSITIVE you have a T25 and not a T28 or some other turbo.

 

[a351must2]

It could be something like I ran into when I first bought my '96 GST. I would experience the equivalent of fuel cut only when making left hand turns when it was cold out. I never could figure it out, but when I replaced the fuel pump with a new Walbro, the problem "went away". I believe I'd found some reference to a similar problem that had to do with the o-ring on the output of the fuel pump, but have no idea if that really was the problem.

 

[Eastwood95]

Alright, when i blew my t25 I got a ported 14b and had boost creep, so I was fuel cuttin like a mug around 17-18 psi if i tried to floor it for too long, just got the TRE 34mm flapper installed, boost holds tight but I'm ####ing fuel cutting at 14-15 psi, so i can only run 13 psi right now, and i did the fuel pump rewire already so i'm wondering if its my pump going faulty or my fuel filter or what, i also reset the ecu and the same shit happens just wondering if anyone had this problem before or knows what is going on here......................SO ANY INPUT IS APPRECIATED!
thanks

 

[steve]

Make sure you don't have a boost leak.
If it's leaking then the ECU is seeing higher karmen counts from the MAF leading to fuel cut.

 

[slodsm]

Look for a boost leak for one like was stated before, no matter what you think, fuel has less than nothing to do with fuel cut, it is all air metering. Also are you hitting a brick wall and your tires locking momentarily or is it just cutting out and stuttering like yo uare hitting a 2 step? If it is the latter, it more than likely old plugs. Once you build a certain amount of boost, you are pretty much blowing out the spark. If the plugs look bad, throw in some new NGK's and gap em to around .026 to .029 and it should take care of your problem, let us know whats up man.

 

[Eastwood95]

my boost controller locknut wasnt tightened down well enough and the controller was spinning freely back and forth by itself, but was reading pretty steady on my boost gauge, I tightened it down and runnin rock steady 15 lbs again......

 

[Patter$on]

ever since i got my 3inch exhaust on my 98 gst it tends to get up high in boost since i dont have a controller and when i get above 17psi normally it bucks and feels like fuel cut well today i got on it all the way through 4th gear and now every time i get to 16psi it feels bad fuel cut.

is it fuel cut


or is my turbo going bad

im gettin a boost controller soon and a 16g but wanted to know whats happening

 

[MadPSI]

My friend has a 92 tsi fwd and running stock boost, with the timing set (checked that) and even switched out MAFs, it will fuel cut @10 psi only in first gear! what would cause just a fuel cut in 1st? it pulls hard through the rest of the gears.. im lost, any help is greatly appreciated..

thanks

-Brian

 

[MadPSI]

could it be weak injectors? the car is completly stock with only free mods, minus the fuel pump re-wire, it has 165k on it and wasnt very well taken care of by previous owners..

im stuck on thinking its injectors or maybe 02 sensor

someone has to have an idea...

 

[Defiant]

Don't wind up in first gear, there's not enough load on the engine.

 

[Speed112]

I have a very lightly modded gst w/ the t-25 still bolted on. I was having problems w/ fuel cut like symptoms. These symptoms included a total cut out in third gear at about 5,000rpm at full boost (12psi)and sometimes it would happen in other gears also. The problem also includes rough idling especially after a full boost run! I thought I was experiencing fuel cut but I knew that I did'nt have enough mods done yet. Here is the diagnosis.

There is a adj. screw on you throttle body housing by your P,E,A vaccum hoses. Mine was very loose and had vibrated out. On inspection of my brothers GSX I found that the idle screw should be backed out about 3/4 of a turn from fully screwed down. Mine was about 1 1/2 screwed out. PROBLEM SOLVED!

 

[MadPSI]

it turned out to be a bad BOV


its been doing good past couple of days now, then started sputtering alot under a load at low RPM and at about 15psi, i think its the ignition coil now...ehh..