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

 

[shingevo]

i am starting to have the same problem with my 91 GSX. after it warms up it will idle surge from 1000 to 1500(up and back down again). Then it will stop. then after i drive for about five minutes the idle will drop to about 500 and seem like its gonna stall, if i try to drive during this it will buck and barely move until 3000. Someone looked at it and said it was the throttle body and that i need a new one. Are there any other suggestions? I tried putting new plugs and wires so far.

read this maybe it can help http://www.vfaq.com/mods/BISS-1G.html

 

[shingevo]

ok ummm my BOV is ok and my TPs sensor is to spec..and thats all i think that can do that....
i am leaning toward my MAF sensor
because when i unplug it it stops surge but gives me different problems... this stinks

check spark plugs or try this http://www.vfaq.com/mods/BISS-1G.html

 

[oldman]

check your BOV and make sure its vented.

You mean not vented.

ok i read a post and i unpluged my MAF and it didnt surge and it let me go inbetween 2000 and 3000 a was all happy then after driving it down the street it started sputtering and when i would shift to the next gear from high rpm'ing the gas would almost seem to cut off but it wouldent die

Yes, that does sound like it's the maf. Did you hack it? Anything done right before the problem? You pick one up for $15 used, make sure you reset the ECU after replacing the maf to clear the CEL.

i am starting to have the same problem with my 91 GSX. after it warms up it will idle surge from 1000 to 1500(up and back down again). Then it will stop. then after i drive for about five minutes the idle will drop to about 500 and seem like its gonna stall, if i try to drive during this it will buck and barely move until 3000. Someone looked at it and said it was the throttle body and that i need a new one. Are there any other suggestions? I tried putting new plugs and wires so far.

how much vacuum are you pulling at idle? I suggest to start with a boost leak test as I suspect you have vacuum leaks.

 

[alex99gst]

My problem first started when I began modding more and more and getting more and more airflow. For example I got a dejontool intake, went to the supra sidemount, and turned up the boost a little bit (12psi.) This was my first time experiencing fuel cut . I fixed a couple leaks that the previous owner had unplugged some vacuum lines and left them unplugged and my vacuum went up from 14 to 16Hg. I had to turn the boost down again and I kept it at a steady 14psi. I knew I was still very vulnerable to fuel cut and so I drove accordingly only to find out that when I got on the interstate tonight that my car felt horrible under any boost at all in 5th gear. I am no expert, but it sounded like the car was misfiring like crazy and it just didn't sound healthy if I began boosting at all. I started hitting fuel cut at only around 5psi and around 3k rpm's tonight. Tomorrow I'm going to check the plugs (replace if necessary) and unplug the battery to reset the ECU (I should have done this sooner but haven't since I've replaced O2 sensor and many other mods) and see if that helps at all. I've read many threads on fuel cut and what causes it and I am more than confident that with my many mods towards improving airflow and small 16g that I am overflowing the MAS. Any advice/information you can give me would be greatly appreciated. Also, here is a log from a while ago before the sputtering mess started on the interstate. I included a picture with the log. My timing looks crazy I know I need to have the base timing checked out because the previous owner claims he did a timing belt job on his own and he "knew what he was doing" I also just noticed that I have no BS belt. Yikes, my car is a timebomb

 

[oldman]

Alex, what was the conditions at the completion of you leak test, how much and for how long was the intake tract able to hold? -16inHG tells me that you're not done with the leak test yet, I use to idle at -18 and thought that was good until I fixed all the little leaks in and around TB and now I'm pulling -21inHG. I also do not think you are overrunning the MAF with the small 16G, not at 14psi anyway.

 

[NitrousPete]

Looking at your log, you're O2's are going really low at higher RPM.

Do you have a long with your TPS voltage or %? Normal O2's (non wideband) will not read constant AF unless you're at WOT. Anything less than WOT and they will switch like normal and interfere with log readings.

If you were at WOT for the whole log, then you're definately running lean there.

 

[alex99gst]

New test found a huge major leak on the turbo outlet elbow Fixed that and it ran beautifully and gas mileage went up like crazy. After a night of driving around with some friends, I was only taking her to 5k rpm's max. After a while again I turned up the boost and hit fuel cut again . I turn it down some more and now it still hits fuel cut in third gear at 11psi. I'm going to check for leaks again, but man I sure hope it isn't the high quality home depot 4 ply silicon hose couplers :sarcasm: I'll try to fix that stuff

 

[~laser_craver~]

I have my car running great pulls really hard and everything is great. Minus the fact that every once in a while not every time but every once in a while when reaching 5-7k rpm while under acceleration in sometimes3rd but mostly 4th and 5th gear it will just hit like a wall.... Just stops accerlerating and boggs down but after i let off i can stab at it again... Can anyone tell me what this is and what i need to do to fix this?

 

[91gsxboosted]

How much boost are you spiking to?

 

[~laser_craver~]

the boost controller is all the way down, and it never goes over 10psi so it doesnt seem to be creeping to me

 

[oldman]

Boost leak test.

 

[~laser_craver~]

ok ill do that tomorow thankx. after elimintating all the leaks do you think that will eliminate my problem?.... i had the inner throttle body gasket leaking really really bad and it wouldnt even idle and i fixed that and it works great now other then that fuelcut type thing i described

 

[oldman]

ok ill do that tomorow thankx. after elimintating all the leaks do you think that will eliminate my problem?.... i had the inner throttle body gasket leaking really really bad and it wouldnt even idle and i fixed that and it works great now other then that fuelcut type thing i described

Boost leak is the number one cause of early fuel cut, one can never rule out boost leaks when troubleshooting for improper fuel cut because it is trigger by excessive air count, not lack of fuel.

 

[~laser_craver~]

dam dude! thankx for the information. your very helpful and you know what the hell your talking about or so it seems to me.

 

[oldman]

You're welcome.

 

[~laser_craver~]

ok i just did the boost leak test and i pump it up and as soon as i stop pumping i hear it a loud hissing so im listening around and i locate it in the manifold/throttle body area. but if i stop pumping i dont have enough time to actually locate the leak before all the air has leaked out of the intake.....

 

[oldman]

Are you using a bike pump? Do you have access to an air compressor or a friend who can pump while you look? Mix a spray bottle of water and dish detergent and spray on every connection there is between the tester and the intake manifold gasket. You can also start the test at the TB elbow first then work your way back to the turbo inlet allowing yourself to work on smaller areas at a time.

 

[~laser_craver~]

ok i got the compressor and it is on the tmming belt side of the intake manni and seems to be under the manifold.... but there is no lines running under there anymore for i have no more emmisions.... and it almost looks like the intake manni gasket, ima get my dad to pump air into it while i feel around the gasket. like i said it leaks out tremendously fast WTF

 

[~laser_craver~]

ok i got it all figured out bro. it is the intake manni gasket. it was blown there was a peice of it hanging out like a peice like 1 1/2'' long so ima order me a new one as well as a inner throttle body gasket because the one sbr sent was way way way wrong it was leaking aswell. tahnkx for all your helpy dude you rule!

 

[oldman]

ok i got it all figured out bro. it is the intake manni gasket. it was blown there was a peice of it hanging out like a peice like 1 1/2'' long so ima order me a new one as well as a inner throttle body gasket because the one sbr sent was way way way wrong it was leaking aswell. tahnkx for all your helpy dude you rule!

Not so fast, spray soapy water on the injector seals, both sides of the TB shat, BISS screw and re-test, you don't want to take things off twice do you?

 

[~laser_craver~]

the throttle body gaskets are brand new aswell as the injector seals they have maybe 20-30 miles on em

 

[oldman]

the throttle body gaskets are brand new aswell as the injector seals they have maybe 20-30 miles on em

So you did end up taking things off twice.

 

[~laser_craver~]

ive taken the injectors fuel rail and throttle body off maybe 3 times in this last week! and now i get to take the entire intake manni off yay! NOT

 

[oldman]

ive taken the injectors fuel rail and throttle body off maybe 3 times in this last week! and now i get to take the entire intake manni off yay! NOT

It's much easier to get to the bottom manifold bolts if you remove the DP and manifold bracket and go from bottom up, especially if you still have the AC compressor.

 

[GSTdude06]

The more times you take off stuff that has a gasket under the worse the gasket can leak. Its compresses to form a seal and everytime you compress it more and more is doesnt seal correctly. I learned that the hard way by breaking off a head bolt on my engine cause my gasketed was compressed and I kept tighting the bolt. Still leaked to......sucked really bad