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

 

[Beanokid69]

I have a tuner magazine and one of the mods it says to get is a Fuel cut defencer and I also know you can have the same effect by cutting a hole in the hunnycomb blah blah blah... anyway I heard that is bad because it just is lying to your ecu about how much air/fuel is entering your engine. what can i do besides that. can i get bigger injectors? would that be the solver and if so is it possible to get to big of injectors? thx



<<<<new guy

 

[JoeWagon]

Sure.
The ECU tells the injectors how long to open by how much air is coming into the engine, basically. The ECU also protects the injectors from being open 100% of the time (high load, not good for the injectors to be at high Injector Duty Cycle). It does this by looking at how much air is flowing. If 20lbs/min airflow means that stock injectors will be open 100% of the time, if you hit 20lbs/min, the ECU will turn off the injectors briefly. That's fuel cut.

OK, the whole idea behind an Air/Fuel Controller (S-AFCII for example) is this:
You can get injectors that are TWICE as large (flow twice as much) and you can tell the ECU that the engine is getting HALF as much air so the same amount of fuel comes in. If the ECU only sees 1/2 the air, it's going to be far from fuel cut.

 

[Devicex]

im sorry but im new with cars so can somebody explain all that plz

...hence why I was not very specific. If you really want to know where to go and what to do, check out the Tuning Guide or do a Search on the issue at hand. There is a wealth of information available on this site and many others, use it to your advantage and learn what you can.

 

[Spyke169]

I've done some searching and I can't find this out, but what physicaly happens when you hit fuel cut? does the pulsewidth change? or timing? Also, at what psi does a 2g hit cut at? i'm hitting at about 11 or 12 psi... i'm creeping to that psi because I have my mbc all the way down. I'm going to be buying a 190lph next week but I was just wondering those few things. thanx guys

 

[dave99gst]

its dont happen at a spacific PSI - its the result of flowing more air then the MAS can handle. if feels like if you were in the passenger seat with your eyes closed and somone floors the car.. then sudenly lets off the gas real fast. sept your the one driving.

 

[Spyke169]

thanks for the info I know what it feels like and it sucks. I was just wondering if there was a specific psi or what. So does anybody know what the engine does to "fuel cut"?

 

[Squackdiddy]

So does anybody know what the engine does to "fuel cut"?

i would also like to know

 

[91TSi FWD]

When the MAS reads too much air flow it will shut down the fuel supply to the injectors as a safety measure for the engine. I've hit fuel cut before, and because you realy don't expect it, it almost feels like hitting a brick wall.

 

[doug]

I'm going to be buying a 190lph next week but I was just wondering those few things.

Just getting a new fuel pump won't help. You'll need some kind of air/fuel controller, such as a S-AFC.

 

[Mystic511]

Have you tried turning down your boost to see if the fuel cut problem is still there? I've been told that you should go over 14 psi without fuel upgrades.

The lower honey comb being removed on some cars does cause it to have wacky idle, which is why i left mine on. I just removed my silencer.

 

[TalonBoy90TSI]

turning down the boost might help but what i dont get is that i have a 1990 tsi fwd and im runnin 15-16 psi no fuel cut...it didnt even hit fuel cut in the winter

 

[TheTSiGuy]

ok so i call the guy today who i bought the car from and he said that it didnt start to do this till he got the head replaced..whats that mean

15 psi stock is the outer limits. you should be hitting fuel cut around there.

You hacked the MAS, might as well do a fuel pump rewire. that will help ALOT at WOT.


Ive heard rare instances of the stock FPR getting weak and the base fuel pressure getting wack...therefore being able to run richer and run more boost.

But yeah, I think that your fuel cut is from running boost near the limit. try setting down to 12 and see what happens.

 

[TalonBoy90TSI]

i didnt hack the mas the guy b4 me did..cant i replace the lower honeycomb?

 

[NOSLO2PT0]

sounds more like knock or a mechanical engine noise that is setting off the knock sensor, resulting in pulled timing. Do a few 3rd gear pulls to redline using a datalogger. Then give us the results.

 

[Pearl90TSI]

Bigger injectors wont cure fuel cut. Fuel cut comes in whenever the computer thinks that it cant supply enough fuel for how much air there is. Remember, your computer doesnt know if they are 350cc injectors or 1000cc injectors, all it knows is what it came with from the factory.

 

[starr]

yes. bigger injectors will help WITH the maft. thats what the maft is there for. to "trick" the ecu into seeing the amount of air the maft wants it to see, and not how much air is "really" there. but i fixed this problem. i just tapped my rpm wire and "leaned" out my base dial one setting effectively telling my ecu i have smaller injectors than i really do, that way my maft sees less air, and adds less fuel, doesn't hit fuel cut, and i'm running perfect. 02 readings at around .96-.98 all through the rpm band at w.o.t. from 3k to 7k, and fuel trims at zero. so my problems fixed. hopefully this will help others that may have the same problem. now just to buy that 14b, bolt it on, and start all over! tuning is good and fun!

 

[MattnGsx]

Just wondering if it's possiable to get fuel cut even with a fuel defencer?

I'm currently running
T28 killer at 15psi
stock 450cc injectors (I have a set of 650's not installed)
255 fuel pump
maft blow though translator (uicp) values all set to zero, all switches except
#3 are off (fuel cut defencer)

now as I understand from what I have read "fuel cut only occurs when the ecu see's to much air?!?!?!" correct? If the fuel cut defencer is activated the ECU now can't see how much air is passing thru Correct? How is it possible that i'm still getting "fuel cut"?


-Matt

 

[starr]

wait a sec. i just re-read your post. all switches aren't supposed to be off. re-read your maft directions, or when i get home to my car i'll tell you what they're supposed to be at. that could be your whole problem.

 

[MattnGsx]

wait a sec. i just re-read your post. all switches aren't supposed to be off. re-read your maft directions, or when i get home to my car i'll tell you what they're supposed to be at. that could be your whole problem.

1,2, and 4 are off, #3 is "on" the fuel cut defencer. I shoulded have worded it better. So it could be that the injector duty is cutting out, though I smell gas when It cuts out.

I also forgot to mention, I don't have my 255 rewired, would this do it?

Anyone out there who can elaborate on these ideas?


-Matt

 

[fertez_turbo]

You are more prone to hit fuel cut on a cold day rather than a hot day because of the air density.

 

[fertez_turbo]

Get a logger ASAP. How do you expect to tune it without one? I bet your injectors are being maxed out.

 

[white95tsi]

I've tried the search for a couple hours now and can't find anything similar to my problem. First off my mods are K&N filter, dejon tool UIP's, 1G bov, NGK plugs, and all the free mods.

The problem started shortly after my install of my UIP's. After they were installed I had a small stuttering problem. After some research I changed my plugs and found a boost leak between the pipe and the throttle body. After a home-made gasket was installed the car ran great..... for about 4 hours. Just after I left the local tuning shop (after ordering boost controller, AF guage, boost guage and guage pod), I'm traveling down the road, hit the gas, and at about 3300 rpm, it feels like someone yanks my ebrake. It happens again so I pull over to make sure I tightened all my intercooler pipe fittings. Everything checks out fine.

So I go back to the shop, and they say that I'm hitting fuel cut, and I need an HKS fuel cut defencer. I was hesitant on that before some research, so here I am now. From what I've found the FCD is not a good idea, and everyone suggests AFC, injectors, fuel pump. All the cases I've found were with and upgraded turbo, exaust, or crazy boost levels.

My question is, can fuel cut happen on a nearly stock 2g. I've checked the turbo for shaft play, done a compression test, all the scheduled maintainance (including timing belt), and the car seems to be in good shape. The only other thing I could think of is that the home-made gasket may have fallen apart slightly, and part of it was sucked into the throttle body. The problem came out of nowhere it seems like, and is much more violent than the stuttering I experienced from the boost leak.

If anyone has experienced the same problem let me know. And if it does sound like fuel cut, I really dont have the money for the fuel mods, so do you think that the FCD would be ok in my case, or at least ok for a temporary fix until im ready for exhaust and the fuel mods.

 

[kyle h.]

sounds like fuel cut. i would check the gasket. and check for boost leaks again. im in the process of fixing my fuel cut problem on a stock 1g. everything's checked out on mine, but i can't hold constant fuel pressure. so i'm still trying to fix it. but an afc isnt a bad idea for a next 'mod' expecially if you're experiencing fuel problems....also a pocketlogger of course. good luck

 

[white95tsi]

I was just outside again visually inspecting everything, and I noticed that on of the hoses coming off the BCS popped off the air intake hose. I must have knocked it off while checking for boost leaks. I popped it back on and I'm still getting the same problems. Could that have caused any problems that I'm unaware of, or could that have caused the fuel cut problems?

 

[blcknspo0ln]

I'm leaning on the fact that it's a boost leak. probably the most common cause of fuel cut.

and no, you can't check for boost leaks visually.. build an intake tester [ vfaq.com has directions ] and run it through. i garauntee you still have a leak in your UICP somewhere.
and also, i'd advise against an FCD.. basically just a bandaid for a gunshot wound. but yea, take 5 minutes and run to home depot and put together a test, spray some soapy water and find out where she's leaking.

and if that doesn't work then check if your fuel filter is clogged

*edit* i've also found that where the rubber hose that connects the UICP and SMIC , the boot has to be sitting perfectly.. or else the clamps will clamp and get tight.. but will still leave an opening under boost.