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

 

[andymoraitis]

Although you have a 255 fuel pump, the 3" DP is likely causing boost creep. That being the case, the car is most assuredly exceeding the range for stock injectors and, wham, you hit fuel cut. I experience this in cold weather with a 16G running all stock fuel at anything above 15-16 lbs. You can turn the boost down for now, but the eventual solution will be to add fuel injectors and some form of air/fuel control.

Dial it down a bit and see if that helps.

 

[VtecRex]

*subscribes to thread* I have a simailar problem, once I get to a spot (like 4000rpms) when the turbo would normally spool up, my car does what you are describing. I dont think it is fuel cut, because my car still accelerates... just really slow. But, if I just give it like 3/4 throttle, it accelerates like normal. I am assuming it does this weird thing only at WOT, becuase your o2 sensors are inactive at WOT, but active everywhere else... so maybe the computer is sensing the loss of pressure with the o2 a/f readings, and correcting it, but at WOT, the car is on its own.

This problem also occured around the same time I tore my upper intercooler pipe connector. So I am almost sure it is boost leak.

Sorry for the long post... I just want to make my similar problem know... I hope I didn't confuse you. Just make sure you let us know the results of your pressure test.

 

[oldman]

With current mods i am hitting fuel cut at 14psi, why is thet? I heard some people run this much boost with no mods with out a fuel cut.

One of the most common cause of early fuel cut is boost leak.

 

[Ian M]

Fuel cut does not have anything to do with the flow of the fuel pump or the limit of the injectors.

It is a safeguard put into the code of the ECU by the factory. When the MAS sees a certain air mass limit,it comes into play. It was put there to protect the engine in the event of a wategate failure,etc and also to limit the amount of power the engine could produce for warranty purposes.

The reason upgrading the injectors and using a fuel controller tends to push off fuel cut,is that the ECU is "fooled" into seeing less air mass to compensate for the injectors.

Like oldman said, start by checking for leaks. If there is a leak,the turbo is working harder (thus pulling more air through the MAS) to maintain the level you have set it at. Cold weather will bring on fuel cut quicker because cold air is more dense.

All cars are different,it will happen to some sooner than others.

 

[moliver]

Im pretty sure its fuel cut.

But i am at 5k rpms and around 16psi and my car jerks. I have my msd rev limiter set at 7k

I installed a fuel cut defensor.

 

[moliver]

ttt

 

[moliver]

up again

 

[Eclipst]

I had this problem some time ago last year, and realized I had my wastegate vacuum in the wrong spot.

 

[GSXTCY]

Bumping is not permitted here. People will find your thread no matter where it is in the forum. If someone wants to answer to your thread they will.

 

[freak4jesus_bt]

Hey guys, I'm needing some advice.
My car was basically stock until my turbo blew a few weeks ago. I went and bought a used Big 16g from Joe Padilla down in Fort Smith, I also bought a boost gauge, an oil line for the turbo, and a 3 inch downpipe. I've put the turbo (and oil line from the oil filter housing) on, a K&N air filter, the boost gauge, and a TurboXS MBC. I have the controller set at 15 psi, and I hit fuel cut once. I was just doing my 'light pole' test out by my house when it happened.

I know that 15 psi should be safe for the 14b, but what about the Big16g?? Will putting the fuel pump in help against fuel cut, and will the new fuel pump affect my gas mileage?? I will be doing the rewire soon, but just not at this time. Thanks for the help.

 

[andymoraitis]

I'm kind of in the same boat as you with the 16G. I usually hit fuel cut at about 16 PSI when doing a WOT pull in 3rd gear (1st and 2nd don't care because the duration under boost is shorter and the load on the motor isn't as heavy). To answer your question, yes, the 255 will help, but you will certainly need an adjustable fuel pressure regulator since the car will run pig rich with that pump on the stock regulator. Some people get away with not running one, but keep in mind that running rich will kill mileage. As far as boost goes, I would dial it down to 12-13 PSI just until you get the pump and regulator installed and then you can likely go to 16-17 without fuel cut issues.

Hope that helps

 

[andymoraitis]

FYI, you may also want to consider a 3" turbo back exhaust and cat to go with your downpipe. I didn't see that in your mod list and thought you might want to consider that next so that the car would breathe a bit better (good looking ride by the way)

 

[PaleDSM]

Fuel cut has nothing to do with your fuel system or what pump you are running. It is airflow related. You flow over a certain amount of air through the mas and you hit fuel cut.

 

[freak4jesus_bt]

The 3 inch turbo back will probably come this summer. I'm having to wait for the funds.

 

[illusioneclipse]

I read every post on this thread and still dont know how to stop or reduce fuel cut. After i installed my evo3 turbo, at 5000 to 7000 in WOT, my car would completely stop and it feels like a strong rope is tied to the rear of my car to a pole.

 

[noreaga0221]

I read every post on this thread and still dont know how to stop or reduce fuel cut. After i installed my evo3 turbo, at 5000 to 7000 in WOT, my car would completely stop and it feels like a strong rope is tied to the rear of my car to a pole.

Its obvisous you do not understand fuel cut. The ecu fuel cuts when it senses too much airflow. It programmed to think of the fuel limitations of the stock fuel system and a totally stock car. Incase on an overboost on a stock car, the ecu stands up for the defenseless engine by making the driver shit himself and therefore slow down. You are getting alot of airflow and the ecu doesnt like it. Get bigger injectors and a afc and tune it. Or get an ecu programmed to remove fuel cut.

 

[unior]

I read every post on this thread and still dont know how to stop or reduce fuel cut. After i installed my evo3 turbo, at 5000 to 7000 in WOT, my car would completely stop and it feels like a strong rope is tied to the rear of my car to a pole.

nah it just feels like your tranny fell out

usually i look in the rearview for pieces of the car

 

[andymoraitis]

I've become incredibly frustrated with my experiences with fuel cut. Initially, I was under the impression that this was triggered by a true lean condition and not a perceived lean condition based on excessive intake airflow. I have a 98GSX with 16G, Injen Intake, 3" Cat Back, stock injectors, stock fuel pump, Buschur MBC (set to 15PSI) and a Buschur UIC with a 1st Gen BOV. When Buschur did the upgrades and set the boost, the car would run beautifully through 1-3 all the way up to 7200 without fuel cut.

Since that time, we've had a few colder days and the car now hits cut at 5500 RPM in third. 1st and 2nd will spool to 7200 just fine however. In my quest to fix this, I've ordered a 190 Walbro and will be installing this in a week or so. Now that the long spouting descrition is complete, I have the following questions for you guys.

1. If fuel cut is triggered by the amount of air passing the MAF as the turbo spools, would dropping the boost down to say 12 PSI allow me to at least run through all of my gears to redline without tripping fuel cut? I could always up the boost in warmer weather, but that's really not what I'd like to do as a solution.

2. How many of you would recommend an FCD. I know that on 93-94 pump, I can run this turbo at 17 PSI with the 190 and stock 450cc injectors (I think I'd kill at this point just to be able to do that). This isn't a matter of me wanting to run 20 PSI on pump gas without supporting mods.

3. If I use an AFC on stock injectors and an upgraded fuel pump (I have a Field SFC_R which allows me to tune in 1000 RPM increments and ramps them evenly in between adjustment points) should I tune for leaner or richer conditions from 3000-8000 RPM? Which one would push fuel cut off.

I have to be truthful in saying that this is getting amazingly frustrating. I miss being able to slap parts on a car and have the ECU learn and adjust accordingly. I really don't want to go with an SAFC-2 and have modest horsepower goals for the car. As I mentioned above, I'd just love to be able to boost it to 17PSI without whacking cut in cold weather. Thoughts and feedback would be appreciated.

Thanks

 

[oldman]

Since last work done involves the intake track, it's possible the clamp on the uip was not tighten again after initial warm up. Check for a boost leak, it could be the cause of the fuel cut.

 

[andymoraitis]

I've checked for boot leaks and clamp tightness throughout the intake tract and intercooler piping and everything is tight.

 

[oldman]

I've checked for boot leaks and clamp tightness throughout the intake tract and intercooler piping and everything is tight.

Make sure you do a real boost leak test not just a visual inspection. I used to think I had no leaks until I hooked up the compressor.

 

[illusioneclipse]

Its obvisous you do not understand fuel cut. The ecu fuel cuts when it senses too much airflow. It programmed to think of the fuel limitations of the stock fuel system and a totally stock car. Incase on an overboost on a stock car, the ecu stands up for the defenseless engine by making the driver shit himself and therefore slow down. You are getting alot of airflow and the ecu doesnt like it. Get bigger injectors and a afc and tune it. Or get an ecu programmed to remove fuel cut.

I do have bigger injectors and AFC2. what should i do when adjusting the afc? Srry, kinda learning about this stuff.

 

[just_passed_you]

Alright guys... I did some searching yesterday afternoon and read a few posts on fuel cut and also what vfaq had to say about it. The boards say it has something to do with fuel, the vfaq says it's not much to do with fuel. My understanding so far for possiblities:

1.) too much unmetered air goes through and something sees too much cfm, ecu kills fuel.
2.) micture of fuel is too rich, duty cycle on injectors @ 100%
3.) high boost levels
4.) ecu being replaced fixed a 2g
5.) wastegate was hooked up wrong for someone

Per VFAQ:
There are no modifications that can do so, aside from an ECU upgrade that eliminates fuel cut. Upgraded fuel pumps, injectors, and fuel pressure regulators do nothing to avoid or eliminate fuel cut. NOTHING.

So...

my story, I'm running stock injectors, stock fuel pump, lower honeycomb removed, MBC..
91 Tsi AWD
With my SAFC and no data logger (which I'm sure is pure genius)
I was getting fuel cut (pulled teeth out of the steering wheel)
at around 4 - 4500 RPMs 11lbs boost.
I leaned out the high and low.. the high I leaned out around -20% and
I made it past 6k, no fuel cut. This experiment was freakishly scarry considering
I don't have the funds to repair a fried motor (once again, pure genius)
After doing a run with -10% all the way across the board on the hi rpm settings
I still ran through 6k RPM. Now.. I upped the boost to 14 or 15 and BAM fuel cut
BUT not at 4k.. now it gets to about 5k and cuts out.

I think it's all to do with fuel/air mixture and I'm looking for a definitive answer.
Any ideas?
Thanks!

 

[just_passed_you]

I started a new thread

http://www.dsmtuner.com/forums/showthread.php?t=929&page=3&highlight=Definitive+Fuel+Cut

it's in another section.

 

[noreaga0221]

Alright guys... I did some searching yesterday afternoon and read a few posts on fuel cut and also what vfaq had to say about it. The boards say it has something to do with fuel, the vfaq says it's not much to do with fuel. My understanding so far for possiblities:

1.) too much unmetered air goes through and something sees too much cfm, ecu kills fuel.
2.) micture of fuel is too rich, duty cycle on injectors @ 100%
3.) high boost levels
4.) ecu being replaced fixed a 2g
5.) wastegate was hooked up wrong for someone

1. Yes, that is the only reason
2. a/f has nothing to do with it. duty cycle can be 100% and still be lean
3. yes but that goes back to #1
4. Only if the ecu was the only reason, not too much airflow
5. Yes, but that goes back to #1

What is so hard to understand? The ecu sees too much airflow. Only solution is to get bigger injectors. Then you must use an afc to reduce the airflow signal going to the ecu because otherwise the ecu still controls the bigger injectors like stock resulting in a undesirable a/f ratio. If you fuel cut at 2500hz, if you put -10% correction on the afc, the ecu will now see 2250hz. No more fuel cut.