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

 

[David15151]

If you are going to get a 2g mas then you should just get the MAFT to tune it instead of the S-AFC. Yes the 660s are plenty for a 14b .. or even a 16g. If you are going to get a AFPR get an aftermarket one that can adjust up and down.

 

[DSM Jeff]

i'd go with the maf and translator and if you already have 660's then your ready for a turbo upgrade. i'd really look into a afpr because you're going to pushing a lot of fuel for a 14b i think. you may not be as fast as you think just going up to 22psi. depending how you set your car up, it maybe quicker or more efficient at lower boost

 

[n0va91TSI]

What is the variable that initiates fuel cut? Is it air mass, duty cycles, knock sum, timing advance?? And what value is the variable when fuel cut initiates?

 

[scottsee]

its a combination of things. http://www.pocketlogger.com/index.php?pid=params&param=airvolume&type=dsm

 

[Boostmonkey]

I will crosspost the simple writeup i came across tonight on the RRE site:

Fuel Cut

It's a nice cool night out and your Eclipse was running better than ever. You were boosting a little higher than you normally do and BAM, the motor shuts off hard and there is a backfire. You ease back into the throttle thinking you just blew up something big. The car seems to run fine. Welcome to Fuel Cut.
You were just flowing more air through the MAS than the ECU was programmed to deal with.

There are several possible solutions to fuel cut. The dime store FCD works fairly well but is potentially dangerous and doesn't net consistent results. It doesn't really solve the problem but is a partial workaround. The next solution is to get the Fuel Cut removed from the ECU altogether via TechnoMotive. This definitely does the trick but still doesn't really solve the underlying problem of running lean. Ideally you should install larger injectors and a fuel computer of some kind, like the AFC.

Fuel cut is caused by the ECU seeing a large airflow value from the MAF which works out to roughly 100% duty cycle on the stock injectors. If you install 550cc injectors which are 18% bigger than the stock injectors, then adjust the AFC to compensate for the larger injectors, you won't hit fuel cut until you
make up that 18% airflow buffer. Ideally you should get the injectors, AFC and the Technomotive ECU mods. This gives you safe, consistent fuel and allows you to run ridiculous boost levels without running too low on fuel or hitting fuel cut.

Also an EGT is generally a good idea once you start running high boost levels or hitting fuel cut. The ECU thinks you are getting close to maxing out your fuel system, and the EGT can tell you for sure. It is an expensive item, but cheaper than an engine. Just get the GReddy electronic gauge and mount it in the #1 or #2 exhaust runner. You will also need it to tune the car properly with a fuel computer.


The rest of the article can be found here:

http://www.roadraceengineering.com/newafc.htm

Good luck

Dave

 

[eclipsegsx1736]

Well, I just got my liscense so I decided to go cruising around my neighborhood. I gave it about 1/3 throttle in 1st gear and took it up to about 5000 RPM at which point the car "gave up", the RPMs stayed around 5000 and i heard the BOV release slowly as if I rolled off the throttle. I then did this again but this time held it for about 3 or 4 sec and then the car felt like i let the clutch out too quickly, it bucked slightly. I suspected fuel cut, but ive never felt fuel cut before. I then shifted into 2nd and took the RPMs up to 5700 in 2nd with NO probs at all. I also tried giving it like 50-60% throttle in 1st and it went up past 5500 with no problems at all. It seems to only do this at low throttle in 1st gear only. The max boost of the day was about 10, so its not over boosting at low throttle, but the boost does go higher if I get ont he gas so its not leaking. Any ideas??? You can see from my mods im pretty much stock, Im wondering if my vented BOV is causing this? (I bought the car vented so dont call me a ricer, im gonna get it recirculating eventually if I have to)

 

[oldman]

I suggest reciculate it and come back for more if needs.

 

[blcknspo0ln]

Im wondering if my vented BOV is causing this?

ghetto rig some sort of coupling from the BOV back into your intake

 

[eclipsegsx1736]

OK OK, ill recirculate it eventually, but besides this could it be anything else? Its gonna be hard for me to recirc it cuz i love the sound so much....... gonna miss it. any other ideas?

 

[slow_talon]

hi you all dsm'ers well i have a 95 eagle talon tsi auto well the problem is that i can't go past 16psi without hitting fuel cut i don't know what the problem is but i'm just getting tired this are my following mods: t25@16psi, walbro 255lph, injen intake, 2.5" dp and exhaust, blitz bov. i'm thinking of buying an afc and some injectors but i don't think will need them right now for the t25 if someone had these problem before help me please. thanks for your time

 

[krazywhitboy]

check for boost leaks...

 

[CanadianTSi]

I had the exact same prob. when I was forced to vent my BOV for awhile. Recircd it and the problem went away.

 

[slow_talon]

does that have anything to do with fuel cut?? if so how can i check for boost leaks what do i need.

 

[pacent]

OK OK, ill recirculate it eventually, but besides this could it be anything else? Its gonna be hard for me to recirc it cuz i love the sound so much....... gonna miss it. any other ideas?

Do it right and get a blowthru setup.

 

[FullthrottleGST]

dude recirculated bov is very loud to me already. i had the stock 2g bov and air filter only. it was pretty loud, so just plug it back, and you'll still have the nice sound.

 

[karbon]

I feel the need to bring this back because I just had the same thing happen to me, and it's better than posting a new thread which will probably make the mods happier.

This has happened only a handful of times. Just like the guy above me, I'll just step on the gas, the car will boost for a bit, and then a huge jolt, which honestly feels like I rear ended someone going about 10MPH. It's enough to make me wonder if I broke something every time it happens. It's a violet and sudden shudder which happens so seldom that I can't seem to get a log of it. I have one KNOWN boost leak at the 1g throttle body, and fixed many others this summer. Suspects may be the fuel filter or my plug wires, as I put in new NGK plugs in August. It always happens at partial throttle boosting around 10 - 12 PSI (I'm running a 1bar spring). Has anyone that had this happen and been able to fix it?
In the mean time, I'll do another boost leak test and fix that shitty throttle body and let everyone in on the results.

 

[sential]

sounds like fuel cut to me... I thought I fixed my fuel cut issues, but it got me the other night when it was cold here too. It's scary, cause you're haulin ass, then boom...and your like "did my motor just blow".

Also check your plugs and your plug wires.

 

[Darksyne]

Here's a good descriptive thread from a few weeks ago:
http://www.dsmtuners.com/forums/showthread.php?t=152805

 

[karbon]

Well if it is fuel cut, my question would then be: why am I hitting it at only partial throttle boost and not full throttle? It doesn't matter whether it's hot or cold outside. It doesn't seem to effect the likelihood of it happening. I definately have enough hardware to support the measly 15# of boost that I'm running, so I don't exactly understand why I would get it. It'd be interesting to log it with DSMLink to find out for sure if it is fuel cut. My pocketlogger doesn't scan injector duty cycle obviously. Anyway want to donate a chip?

 

[mastadogg2]

dont mean to change the subject but my car is running so rich if you get out with it running you will pass out.. 100% gas smell.. and now it refuses to boost past the 13psi range... would this be a boost leak? .. and i got a problem with my throttle.. sometimes when i push in gas i get a hesitation then it kicks in and jerks the car.. how can i fix that? for my recent mods check www.cardomain.com/id/mastadogg2

thanks

 

[naspat99]

i currently put on a big 16 with a injen intake and spearco intercooler and buschur upic with a greddy type s..... now when i get on the gas it goes to about 5 to 7 punds than starts blowin off by itself i dont have any fuel system upgrade other than a walboro 255 pump ..........no boost leaks and BOV is hooked up correctly any ideas i would appreciate it

 

[Talon96tsiAWD]

sounds like the bov spring is too loose.

 

[naspat99]

do you know how i can check/fix that.... i tried adjusting the softness but that doesnt help

 

[BigBADGSX]

stiffen up the spring in the bov...the adjuster is at the top. My suggestion is adjust a little take a drive and see what it does and keep adjusting till you can get it to hold. If that doesnt work, you need to leak test your ic pipes for boost leaks.

 

[torbs]

sry to bring up an old thread, but i just had my tsi out last night in -20 to -30 degree weather and i fuel cut every time in 2nd gear at 5-6k rpm at wot...damn that sucks, feels like the car is gonna fall apart...