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

 

[spyderturbo007]

I think that under certain conditions such as fuel starvation or inadequate fuel pressure, the ECU will cut ignition to prevent a potentially disasterous lean condition. I bought my DSM used and i bet the fuel filter was old and clogged, so once i did my first exhaust mod the fuel demand was greater, and the filter couldn't keep up with the flow. I got 'fuel cut'. The ECU detects low fuel pressure or a lean condition and cuts igniton to prevent dangerous engine conditions. So, it seems that the ECU might trigger 'fuel cut' in the case of inadequte fuel delivery.

-I do my first exhaust mod, make more power, and get fuel cut.
-I replace fuel filter and change nothing else.
-Fuel cut goes away.

This doesn't seem like coincidence, and supports my theory on 'fuel cut'.

This is absolutely wrong. The ECU cuts fuel based on airflow only. It knows nothing about fuel delivery, nor does it care.

 

[JayRolla]

I was getting a fuel cut around 5k rpm's, but it was not a boost leak. If anything, a boost leak means you need less fuel because less air is getting into the engine.

I replaced my old fuel filter (a big restriction) and the fuel cut went away immediately.

If you have a boost leak the turbo has to work harder to get to its sustained boost level, making it pull harder and over run the maf.

Like he said it has nothing to do with fuel delivery. Injectors, pump wont do anything. A SAFC with correction will trick the ecu to seeing less air so this way you will hit fuel cut way later.

 

[zacksgsx]

once in a while i feel the same thing at 3k rpm but only sometimes, like pulling out of my sub early in the morning when it is around freezing outside. it only happens when accelrating 60-100%. i never feel it in 1st, bearly in 2nd, but 3k in third and slam into the invisable wall i go, before i can react its over. Never hapens in 4th or 5th. I cannot figure it out...

Yep, same here, bang into the wall. When cold out, before engine is fully warm and going into 3rd gear, just coming into the turbo(3000-3500 rpm). Need to figure out how to prevent it. I posted a thread on this earlier. Was advised to check Fuel pressure regulator, size of injectors (all stock on mine). The thought being I need more fuel to prevent the cut-off. TP

 

[JayRolla]

Fuel delivery has nothing to do with fuel cut. How much boost are you running? If you are fuel cutting for no reason than you have major boost leaks. Fix those first.

 

[mhuffman]

This is absolutely wrong. The ECU cuts fuel based on airflow only. It knows nothing about fuel delivery, nor does it care.

I think I am using the wrong term to describe my engine phenominon then. The correct term should be 'ignition cut', because i had inadequte fuel delivery and the computer cut ignition to prevent exploding the engine. Or possibly i ran so lean because of the clogged filter the car hit what felt like 'fuel cut'. Because i had major engine power loss, i replaced the fuel filter, and it ran completely better. But it wasn't fuel cut.

How is it that you can follow the 1st gen power upgrade stages as outlined on this website without hitting 'fuel cut'? Is it possible to do full turbo back exhaust and a MBC @ 15psi and not hit fuel cut?

 

[JayRolla]

How is it that you can follow the 1st gen power upgrade stages as outlined on this website without hitting 'fuel cut'? Is it possible to do full turbo back exhaust and a MBC @ 15psi and not hit fuel cut?

Sure it is. Most 1g's have major boost leaks all over and this is the reason they hit fuel cut. If you have a SAFC you can adjust it so you fuel cut later since you lieing to the ECU how much air is coming in.

 

[nightspeed87]

I got my fuel cut raised by 20 % on my eprom chip so if I were to ever have it it would occur a little later.

 

[GSXBen]

Check your O2 housing. and maybe you might need a port and polish.

 

[Soup Can]

Ok I know sounds stupid, but I'm retracing all my steps again to figure out why I'm hitting boost cut at 11psi and that means going back to the very basic stuff I tested in the beginning. So how long should the system hold pressure...right now I pressurize it to 20psi and it falls at a rate of about 1-2psi per second for the first 10psi then slows down a little after that...fixed all the leaks the first round including a new compressor gasket and new tb seals...and I can't hear/see any leaks with soapy water on pretty much everything...

As far as the boost cut goes happens at 11psi everytime regardless of throttle position, speed, or gear....first time around sealed up all 3 boost leaks...1 at the compressor housing, 1 at the tb and 1 by the egr valve....replaced the fuel pump since it was under warranty anyways to eliminate the possibilty of fuel issues...pulled the plugs and they looked fine and are gapped correctly...new fuel filter and fpr....this is my 3rd dsm and the only odd thing I've noticed this whole time is that when I pulled the fuel pump out it was covered in rust...granted the car has sat off and on for a year, but thats the fastest I've ever seen rust develope on a fuel pump housing...so thinking I had water in the tank or something silly I put in water a bottle of isoheat and a fresh 5g of premium fuel....and still no go...have a datalogger but the palm broke so I don't have any logs I can throw up...is there something obvious and stupid I'm over looking?

92 talon awd...stock turbo, stock i/c piping, stock fuel setup, etc...other than bc at 11psi it runs perfect...no smoking, boggin or anything and it pulls strong all the way too 11psi every time...

 

[TSIMonsteR]

Boost Leak Test FTW....

It should hold pressure long enough for you to find the leaks. Depending on the intercooler setup, I'm guessing the exact time be different.

 

[Defiant]

Fuel cutoff is a function of airflow rate, not boost pressure.

 

[Soup Can]

yep I know that...the only reason I included boost psi is to give any extra reference I could to help others with suggestions...BUT as a kicker its also the same psi i get cut out when I put on a s16g...which is odd....

Monster...hehe as I said I did a boost leak test...thats the question I'm asking...how long should the system hold pressure...

 

[oldman]

Are you saying you can't boost past 11psi or you're hitting a wall (fuel cut) at 11psi? The 20psi on the leak test, was it read from an aftermarket boost gauge or the regulator gauge on the compressor? Assuming you're using a compressor. Do you have logging capability?

 

[Soup Can]

using an aftermarket boost gauge connected to the P-port(also ran it off the fuel solenoid just to check reliability of reading)....100% without a doubt its fuel cut...I just can't figure out why...but the other thing is its 11psi every time regardless if I run the stock 14b or the s16g...no clue if I could build more boost or not, as it never gets past 11psi before hitting fuel cut...logger is broken so no way to log at the moment...i can pressurize the system to 20psi and I dont find any leaks and it drops at a rate of around 2psi per second for the first 10psi, so I was just curious what drop rate it should have with a sealed system...I know it'll lose a little through the exhaust end of things...

 

[Jetblack]

Did it just start happening? Did your mas get any moisture in it which would mess up the sensor and read improperly?

 

[oldman]

I think I am using the wrong term to describe my engine phenominon then. The correct term should be 'ignition cut', because i had inadequte fuel delivery and the computer cut ignition to prevent exploding the engine. Or possibly i ran so lean because of the clogged filter the car hit what felt like 'fuel cut'. Because i had major engine power loss, i replaced the fuel filter, and it ran completely better. But it wasn't fuel cut.

You're most likely not hitting fuel cut, instead you were probably experience ignition timing retard due to knock.

How is it that you can follow the 1st gen power upgrade stages as outlined on this website without hitting 'fuel cut'? Is it possible to do full turbo back exhaust and a MBC @ 15psi and not hit fuel cut?

Because unlike the name "fuel cut" suggests, fuel cut was never designed to guard against fuel starvation, it was designed to guard against runaway boost. "Boost cut" would have been a more approriate name although the method the system uses to "cut boost" is by "cutting fuel", hence the misleading term "fuel cut".

My car still doesn't feel right.I can be driving the road and hit the gas some and my boost gauge will show 8lbs of boost my cars not even pulling.Could someone please give me a link to a guide for checking for boost leaks and how to make a boost leak tester.All help would be appreciated.

Have you tried using the seach function or vfaq.com?

 

[94TalonTSI1]

Boost Leak Tester


A couple of places to look for your boost leak:

1: Stock SMIC. The top pipe that connects to your UICP over time will develop a swiss cheese condition. JB Weld will fix this.
2: Throttle Body seals. Check those
3: Compressor outlet pipe.
4: Make sure your clamps are all tight. They may just be loose enough that they are leaking boost, but tight enough not to blow off.

A boost leak usually also means a vacuum leak. Take a propane torch (unlit of course) and just turn the gas on. Move it around your ic pipes, Intake manifold, etc. If you hear a change in idle, you know where your boost leak is probably going to be.

Good Luck!

Ryan

 

[oldman]

A boost leak usually also means a vacuum leak. Take a propane torch (unlit of course) and just turn the gas on. Move it around your ic pipes, Intake manifold, etc. If you hear a change in idle, you know where your boost leak is probably going to be.

I'm sorry but that is not going to work on the IC pipes because any areas before the throttle body plate will not be a part of your vacuum system.

 

[Soup Can]

I bought the car with bent valves and crushed pistons, so I completely rebuilt it and had the problem since I first started it up...I talked to the previous owner and he said it ran fine before the timing belt snapped....I have 2 MAFs so I swapped them out to eliminate a bad maf sensor...

 

[SleepingEclipse]

Here's the deal. I have a 97 GSX with the mods in my profile. It has NOT been tuned whatsoever. I think I'm running a bit rich(ok, I know I am b/c I can smell the gas when I hammer on it hard and my buddy said I was shooting flames out the exhaust on hard acceleration). I have a MBC and it's set for 13-14psi. If I accelerate a little hard just to get it to boost it will go up to 13 and sit there at 13lbs of boost. If I put the pedal to the floor the gauge will go up to 15psi and around 4.5k rpms the car stutters real hard like something broke. It's like a loud CLUNK. I instantly let off the gas and continue on my way. Any ideas what would be causing my car to do this? It's only if the pedal is on the floor that I have problems. And why is my car boosting past what I have it set for? I am not a total newb when it comes to turbos, but definetly am close to it.

 

[SpeedAddict62]

Your boost is rising because you are getting boost creep. This happens when your wastegate can not bypass enough exhaust gas around the turbine to regulate the turbine speed, so it just keeps spinning faster and faster. Its probably caused by your turbo back exhaust, because it is freer flowing than the stock one. This is what is happening to me. The best way to fix it is to port the turbine housing, wastegate and 02 housing. There is plenty info on here if you do a search on porting, and a vfaq too Porting VFAQ. Porting means removing some of the metal of the housing to make them bigger and flow better and is usually done with a die grinder and a carbide burr. You could do it yourself, or find someone else to do it. The other alternative, in an extreme case, would be an external wastegate, but that would be $$$ and would require welding the internal wastegate shut. My 14b is ported, and that apparently isn't enough. Porting your 16G should do the trick though.

Fuel cut is like hitting a brick wall; the ecu basically shuts down the engine to prevent it from outrunning the fuel system. Is this what you are experiencing, or is it more subtle, like the ecu pulling timing due to knock?

Do you have an adjustable fuel pressure regulator? If not, you are overrunning the stock fuel pressure regulator and this could cause fluctuations in your fuel pressure. (Although, I don't have one myself and the car runs fine. Its something to keep in mind though).

Are you venting that BOV to atmosphere? If you are, I'd suggest recirculating it back to the intake before the turbo. Venting to atmosphere is letting metered intake air out of the engine, which the ecu still thinks is there. I'll tell you that now, before you get flamed for it haha.

Last but not least, I would recommend you get a logger. That will give you an idea of what is really happening with your engine. It will plug in to the diagnostic port and let you log a bunch of signals the ecu sees. Hope this helps.

 

[SleepingEclipse]

Alright thanks for the help. I will look into the porting. I am not running an adjustable fpr, just the stocker. I am venting to the atmosphere(bad bad I know) but that's how it was when I bought it and the only other BOV it came with was another used HKS SSQV. The idle isn't as bad as I thought(actually don't have it fluctuating at all, even when warmed up). I have thought about the logger I'll have to look more into it. I don't think it's a fuel cut. It's hard to explain, I'll try to get a video of it. It's just like the engine says eek then it goes back to normal.

 

[SpeedAddict62]

alright good deal. I recently got a custom 3" turbo back, and even with my 14B ported it was boost creeping from stock 10 psi (I don't have a MBC) to 15 psi. At 15 psi, the puny stock fuel pump couldn't keep up, and it went way lean (14:1) and started missing pretty bad. Of course, neither of us should have a problem running out of fuel with the walbro 255. With my setup now, it still creeps to 15 psi, then starts cutting out (intermittently losing power) even though the afr is around 9.9:1. Sounds like we are experiencing something similar. My next mod is definitlely going to be a logger, so I can see if timing is getting pulled due to knock. Good luck.

 

[taylork057]

i have a friend with a 16g, his car does the EXACT thing to, but his is tuned by me and it still does this. i was thinking it was a broken mount or some sort, but when i hit fuel cut in my car when i had afc with a FPR at 60psi it didnt "buck" as hard as his does.and we both at the time had rc 550s, is this a more extreme fuel cut or what

 

[taylork057]

even though the afr is around 9.9-1.

i wouldnt even use a logger to lean it out. if your only running 15 lbs you can blind tune it pretty well by just pulling more and more fuel