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

 

[air23cary]

my 91 talon tsi with full 3 inch turbo back exhaust, 16g and 14 psi boost is cutting fuel at 6k instead of 7k........is this an easy fix? what is wrong with my car?

 

[leet]

It would be helpful if you filled out your profile for your car.

Turn the boost down.

 

[air23cary]

105k miles, had a compression test done, engine was in GREAT shape, recently rebuilt my tranny, after it was put in my car wasn't running right, so the shop put in a new ecu and that seemed to correct the problem.

 

[PhoenixRPR]

The pigtail connectors for 2 of the injectors were brittle and broken. After that, he found that injector #1 was intermittenly firing with a test probe. After replacing the injector relay, injector connectors, and 1 injector, the car runs great.

 

[Defiant]

Fuel cut is about air, not RPM, PSI nor HP.

http://members.shaw.ca/costall/ECUprimer/ECU_ch7.html

 

[leet]

True, Defiant. However, if you lower boost pressure, you are lowering the amount of air being forced into the engine as well.

Hence my suggestion.

 

[air23cary]

i am getting between 500 and 1000 rpms fuel cut in almost all gears..........mods are listed in profile......how can this be fixed? i just put in the walbro fuel pump thinking that would be it, but it didn't help.

 

[guitarXgeek]

First off, you need a fuel pressure reg for that 255. Injectors wouldn't hurt either . How much boost you running? I wouldn't go above 13-15 psi on stock injectors, simply because you WILL get fuel cut if you go much higher (which is probably whats happening).

 

[SpoolnTsi]

What kinda octane you running? I personally have ran 18lbs on a s16g, walbro 255, stock injectors and FPR no problem. But im usually shiftin at 6500 and we have sunoco 94 octane here which is all i run. You definately shouldnt be hitting fuel cut at 14lbs

 

[doug]

Fuel cut has nothing to do with which fuel pump, octane, or injectors you're using. It's how much air you're flowing through the MAS, combined with some other environmental factors.

 

[air23cary]

i run 93 octane. in buschurs upgrade sequence for stage 1 they do not include a fpr or injectors even though they have a fuel pump, so i am sure i do not need those.

 

[doug]

You can talk about detonation, octane, and all that other stuff all you want, but the fact remains that when the MAS sees a certain amount of airflow, it sends a signal to the ECU to cut fuel. Nothing else matters. That's what I meant by it doesn't matter which pump or injectors you're using.

 

[Syndicate13]

You should also provide some more info as to what the problem is. Is it actually fuel cut or just some misfiring? If you hit fuel cut you will almost be picking your front teeth out of your steering wheel. However a lack of fuel will feel like slight hesitations throughout the rev range.

 

[air23cary]

um i am not sure it is fuel cut since my head does not crash into the steering wheel but the car definitely stops accelerating and i switch gears as soon as possible to prevent any damage. i would say it is a cross between fuel cut and hesitation, if that means anything.

as for leaks, the car has been boost leak tested, vacuum tested, etc.......everything is fine except a small leak in the throttle body, which i am getting fixed next week.

 

[94EclipseGST]

Probably running really rich. After I installed my 255, the car was so rich, it would bog and sputter and get fuel cut around the same time. I had to lean things out with the MAFT.

 

[David15151]

I have a question related to this. You can see my mods in profile. Why it is I DONT hit fuel cut if he does at 14psi? I run 14 psi as well with only a fuel pump as fuel mods. After I installed my exhuast last week I actually creeped up to 20psi and held it for a good 3-4 seconds before i noticed and let off the gas with no hesitation or fuel problem. Why can I hit such high boost with no cut on a 16G?

 

[Syndicate13]

2G's are different. Locally we had 2 guys. One with a 90 and one with a 95. Both had small 16g's, the 90 had a Supra pump, the 95 a 255. The guy in the 95 could run 16 psi all day long and not hit fuel cut, however in the 90, he would get fuelcut with anything over 13 psi. I believe it has to do with the 1G MAS not flowing as much air as the 2G MAS does. It just reaches it preset limit sooner than a 2G MAS. May want to have a wiseman chime in on this as they could confirm it with some hard evidence.

 

[SpoolnTsi]

as for leaks, the car has been boost leak tested, vacuum tested, etc.......everything is fine except a small leak in the throttle body, which i am getting fixed next week.

Get your boost leak in the throttle body fixed and post your results

 

[KC_GST]

I cannot remember if I have asked you guys or not but I recently had an evo motor put into my 2g, It has the yellow top injectors, (510cc i believe) and a big 16g turbo Even with the yellow tops it makes it through first gear then in second at about 5500rpm you can feel a power loss, then the car cuts off. I purchased a MBC and a boost gauge. If I bought a fuel pump would my car be ok running all the boost. I am not even sure how much my car is boosting?? I live in N. Kentucky anyone close wanna help????
Suggestions and comments are also welcome

 

[paranoidTSi]

You need a BOOST GAUGE, this is one of the FIRST upgrades you must have. You should know what you are boosting at all times, its dumb and you are likely to blow a motor if you don't.

What you are describing is fuel cut, and no a upgraded pump is not going to solve your problem. The reason this happens is because the ECU feels there is too much air coming into the motor so it cuts you off. The only solution is to a) get a piggy-back system that fools the ECU into thinking there is a safe amount of air entering the engine b) get a fuel management system that can modify air/fuel settings.

 

[vinh766]

i just installed my new fmic by johnny race car and now im getting fuel cut.

major mods:
big 16g @ 20psi
3 inch turbo back exhaust
2.01 maft
s-afc

those are the mods that i would think would relate to what my problem is. k, every since i installed my fmic, i've been getting fuel cut. i thought that there was a fuel cut feature on the gm maf translator, but i can't seem to figure it out. and with a big 16g @ 20psi, i shouldn't be hitting fuel cut on rc 550cc's should it? any ideas? i'll try to turn the boost down and run it again and log it 2morrow.

 

[vinh766]

does this sound like i need a new fuel pressure regulator? because im still on the stock one. for my fuel upgrades, i have 550 injectors, rewired to a vr-4 fuel pump, and everything else is stock (like FPR) on 93 octane. personally, i don't think that a 16g @ psi should max out my 550's so easily. TIA.

 

[crankbender]

fuel cut is not caused by actual fuel flow. the problem is the ammount of air the ecu sees. If you are exceeding this level the only way around it is to change the code in the ECU....

Getting even bigger injectors will cause you to trim the fuel down and the ECU will see less airflow. thus avoiding fuel cut.

Becuase of this any air leak that is causing more air to be counted can cause fuel cut. Start there.

 

[slow_talon]

i currently have a 2g talon tsi auto i upgrade from the tired t25 to a 14b and i'm having a couple of problems with my current setup. when i installed the 14b i had to run only 14lbs cause the fuel pump couldn't do too much, so i upgraded to a walbro 190lph but the fuel pump only allowed me to go to an amazing (sure)15lbs now i upgraded to a walbro 255lph and this piece of crap only allows me to go up to 16lbs without fuel cut. The other problems is that since my car is an auto if i powerbrake i can only build 2lbs so i don't have no low end power at all. Last week i took off my turbo and everything was fine but then i noticed i had non of my gaskets so i decided to put them all. i'm thinking of buying a torque converter but many people say i should be able to build boost with my stock converter but my stock converter only goes up to 2200rpms when i powerbrake and my turbo starts spooling at 2800rpms might the turbo be already dying? but it doesn't have shaft play at all.

14b@16lbs
walbro 255lph
2 1/2 exhaust
2 1/2 downpipe
blitz bov

 

[ktg-dsm]

got the walbro 255 and am still hitting fuel cut.....why? do i need a S-AFC?