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

 

[joeym4130]

ok i can feel the trany jerk. if it is boost leak how do i fix that

http://www.vfaq.com/mods/ICtester.html

Best tool ever for a DSM Make one, throw it on, pressurize, and play 'Find the Leak", its a fun game

 

[Cool Mr Steve]

So why do people hit fuel cut? Most of the time, the cause is either boost leaks or malfunctioning maf causing inaccurate signals being sent to the ECU.

So, what will happen if I run 17-18psi on a Big 16g without upgraded injectors? Would it be fuel starvation? What physically happens (car dies, risk of detonation, ect) to the car if I set my car to boost levels at which the stock injectors would have to run at, say, 115% duty cycle?

 

[steve]

So, what will happen if I run 17-18psi on a Big 16g without upgraded injectors? Would it be fuel starvation? What physically happens (car dies, risk of detonation, ect) to the car if I set my car to boost levels at which the stock injectors would have to run at, say, 115% duty cycle?

You risk detonation.

Trying to run 115% DC means at best your asking for 15% more fuel than your injectors can deliver and you'll be running lean. Worst case, the injectors can behave erratically at they reach 100% and who knows how much fuel you really get. In addition the coils in the injectors don't get a chance to cool at 100% and can lead to injector failure.

Unless money is no object, don't run boost levels calling for > 85-90% DC from your injectors. Detonation can be expensive.

Steve

 

[punishercb]

I'm getting fuel cut when I try to floor it. I've checked for boost leaks and I only have one considerable one in my throttle body. Other than that I don't have any else. I get it at random times. Most often when I'm flooring it in second though. What is causing fuel cut exactly? Could it be bad wires or something like that? I've checked whatever I can think of and it's still cutting out on me.

 

[oldman]

Are you talking about sputtering or fuel cut, a lot of people get them mixed up until the day they hit a real one. Most people will be hesitant to go WOT after hitting fuel cut because it truly is a traumatic experience for you and the motor.

 

[punishercb]

Hmm, i don't know. I don't know the difference between stuttering and fuel cut. All I know is that when it does it I jerk foward real bad. I've heard about people hitting the steering wheel and I guess it isn't that bad. Would stuttering be bad enough to jerk foward REALLY violently?

 

[oldman]

Hmm, i don't know. I don't know the difference between stuttering and fuel cut. All I know is that when it does it I jerk foward real bad. I've heard about people hitting the steering wheel and I guess it isn't that bad. Would stuttering be bad enough to jerk foward REALLY violently?

If you're not sure than it was probably not fuel cut. I suggest doing the following.

1. Check plugs and wires. If they're old, change them and gap them correctly.

2. Boost leak test.

How much boost are you running? Stock fuel system? Any more details would be helpful.

 

[oldman]

I just went through your old threads, you still have not done that leak test like I suggested a month ago did you?

 

[punishercb]

I just went through your old threads, you still have not done that leak test like I suggested a month ago did you?

Yeah I have! I did that right off the bat! And thank you by the way. I found 4 main leaks, one in the t.b., one in the licp, one from the BISS screw, and the last in the uicp. I have sealed all of those up except for the throttle body.
I doubt I have fuel cut because it really isn't as bad as described. I just ordered some new wires today that should be in tomorrow. I recently replaced the plugs so I don't think that is it. Hopefully the new plugs will solve my problem. We'll see(crosses fingers)

Thanks

 

[oldman]

I found 4 main leaks, one in the t.b., one in the licp, one from the BISS screw, and the last in the uicp. I have sealed all of those up except for the throttle body.

You obviously have re-tested it after you fixed them if you know TB is still leaking, how much pressure were you able to hold and for how long with the TB leaking?

I recently replaced the plugs so I don't think that is it. Hopefully the new plugs will solve my problem. We'll see(crosses fingers)

Make sure they're NGK and gapped to .028". Post back after you check the gap and change the wire.

Thanks

You're welcome.

 

[punishercb]

Okay, did everything you told me to do oldman. It's still happening though. I bought brand new 8.5mm spark wires, and I checked my gap. I didn't get ngk because I just replaced my plugs a month ago with autolite I believe. So it isn't the ignition I don't think.

I am able to hold about 17 pounds for a few seconds. Is that normal? I do have the leak from the throttle body but I'm not sure if that would be enough to make the engine run so bad?

 

[oldman]

I just replaced my plugs a month ago with autolite

What type of plugs are the Autolites?

I am able to hold about 17 pounds for a few seconds. Is that normal? I do have the leak from the throttle body but I'm not sure if that would be enough to make the engine run so bad

Desired results would have been 20 psi for at least 30 seconds. A leak is a leak, I would revisit the TB shaft seal and get it fixed.

Are your pofile up to date? T25, stock fuel pump, injectors and bov? What psi are you running or trying to run?

 

[FedsClipse]

I have a Garrett Hybrid turbo that I'm running with stock fuel injectors and a stock fuel pump. I recently raised the boost from 10psi to 15psi with my SB MBC and now when i hit the gas in 1st the gauge only goes to about 10psi thats flooring it, when i shift the car into 2nd slowly (normal) the car boosts to 15psi just fine, same with 3rd and 4th but when the car is at high RPM say 4000 then i floor it the boost gauge does not go past 8psi. (Thats in 2nd,3rd,4th,5th) The car feels like it just hits a wall. Could this be fuel cut off? I dont know what it could be a boost leak maybe? I just bought a walbro 190 fuel pump should i try that bigger fuel injectors? Any info would be great! Thanks Guys

 

[olmytsi]

I dunno what you are experiencing but you need that 190 and at least 550 injectors in asap before you blow that engine.

 

[Spookcorleone]

If the cars spuddering kinda like it could be a boost leak but I think its the fact that you are having trouble getting enough fuel into the car. Sounds like a fuel cut to me. Once it builds so many pounds it just like... "clunks" down and will operate normal if you don't use your gas / turbo all the way? Right?

Do you have anything to control your fuel? SAFC? DSMLink? Check into it - you are getting to the point of modding your car that you have to know whats going on with its internals so forth...

 

[tstkl]

when i get fuel cut (or at least thats what i guess it is) from my turbo charger running to high psi (mbc wasnt working) my car would make a fatty lurch, like i took my foot off the gas rediculously fast.... i would upgrade the fuel if i were you...

 

[oldman]

I have a Garrett Hybrid turbo

That doesn't tell us anything about the turbo, t3/t4 like in your profile doesn't help either.

You're going about this all wrong, a turbo that size should be the last mod, not the first. Fuel cut has little to do with the fuel system, more to do with air count. You're probably experiencing fuel starvation (running lean) instead of fuel cut unless you have some serious boost leak. How do you expect not to have any problems when you bolt on a turbo that size without proper supporting mods. My suggestion is to remove this turbo or at least unhooked the actuator arm until you're ready.

 

[Spookcorleone]

Yup - thats why I said if it is a boost leak, which I don't think it is (looking at his profile he has 550s and a pump ... ) he needs something that will starts to control them.
I dont really think I would ever do a turbo upgrade without some type of A/F control.

Again him stating the turbo really didn't help or narrow it down, but it sounded like fuel cut to me because when he digs into it as hes saying, it feels like he hits a wall, but when hes gentle with it, runs and operates normal...
(Correct me if I'm wrong but fuel-cut is when your car can't supply enough fuel, pretty much that its trying to work but it is being over run?)

 

[oldman]

which I don't think it is (looking at his profile he has 550s and a pump ... ) he needs something that will starts to control them.

Read the original post again.

Again him stating the turbo really didn't help or narrow it down

Sure it does because fuel cut is air flow related.

(Correct me if I'm wrong but fuel-cut is when your car can't supply enough fuel, pretty much that its trying to work but it is being over run?)

Fuel cut occurs when ECU cuts spark and firing of the injectors because it receives air flow reading exceeding the preset value programed into the ecu, not when you run out of fuel. The most common causes of improper fuel cut are boost leak, defective maf and boost creep.

 

[Spookcorleone]

The turbo he named didn't really bring it into prospective is what I am saying... saying I have a t3/t4 turbo really doesn't say anything about the type is what I was saying...
Hrm.

As for the fuel cut thing - there is nothing in the car that will shut it down if its in danger of running lean? 0.0

As for him stating he just bought a pump, doesn't mean its not on the car... along with the injectors they are both quick installs. I was saying the car would run like crap either way if you upgraded injectors, pump, and turbo but have no A/F control at all...

 

[steve]

As for the fuel cut thing - there is nothing in the car that will shut it down if its in danger of running lean? 0.0

That's pretty much correct. Stock the ECU could turn off the BCS and retard the timing when the car starts knocking but it doesn't shut the engine down. It's still possible to blow the engine up, just harder.
Fuel cut is there to protect from runaway boost. The trigger is mass airflow based.

Steve

 

[CanadianTSi]

Turn the boost down until you have the proper supporting mods...

 

[Defiant]

1.) It's very difficult, and remarkably brainless to look for full-boost in first gear. The pistons get away from the boost too easily because first gear isn't enough load on the engine.
2.) Fuel cut is a function of airflow, and has no relation to boost levels. When the engine sees too much air coming in, it determines that something is wrong and that it's probably the turbocharger running wild. In a desperate attempt to keep the pistons below the head casting, it chops off the fuel supply.

Don't even try to boost in first gear. Use first just to get the car into second.

 

[punishercb]

Alrighty, sorry about the delay. I've been extremely busy. Profile updated too, thanks for reminding me. About the spark plugs, I honestly don't remember what kind they are. I do remember that they're just the normal single tip. Not the double, triple, or quadruple tip. Man, I guess that t.b. shaft seal is way worse than I thought. It takes forever for it to reach 17 psi(I have a compressed air tank) and then leaks in probably 20 seconds. Do you mean the intake should be able to hold 20 psi for 30 seconds??

Also, where's the most common place to get the new seals to rebuild my t.b.? I live in a little hodunk town so autozone or advanced auto is probably out of the question.

Thanks alot for the help so far oldman, I really appreciate it.

 

[oldman]

About the spark plugs, I honestly don't remember what kind they are. I do remember that they're just the normal single tip. Not the double, triple, or quadruple tip. Man

! Just make sure they're not platinum plugs.

(I have a compressed air tank) and then leaks in probably 20 seconds. Do you mean the intake should be able to hold 20 psi for 30 seconds??

More or less.

Also, where's the most common place to get the new seals to rebuild my t.b.? I live in a little hodunk town so autozone or advanced auto is probably out of the question.

If they're the same as 1Gs, you can ask any auto parts store to order it for you. It's made by Chicago Rawhide, part# CR 10X14X3 HM4 R.

Thanks alot for the help so far oldman, I really appreciate it.

You're welcome.