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

 

[oldman]

yea, its when the ecu thinks the fuel system cannot support the ammount of air flowing into the car, i know... but since hes using stock injectors, my guess is that the ecu's thoughs are pretty close to dead on...

If this was true, most people would be hitting fuel cut at about 16psi with a 16g. Fuel cut is triggered by an air count value pre-program into the ECU and does not take IDC, IPW, knock count or timing into account. I think once you start knocking, it's a race between whether enough timing can be pulled in time to stop you from going faster or the air count value been hit. Under normal operating conditions where there are no leaks or out of control boost, bogging down should get you before fuel cut does.

 

[steve]

(cuz you would get the same results if you just took the hose off the wastegate...) can cause fuelcut..

I should hope so since that's why fuel cut exists. To protect against the wastegate hose coming off.

Steve

 

[shallowshowcase]

hey guys, upped it back to 16 psi and all i needed was a retune, as the fmic flows alot more than the smic, wasnt boosting too high just needed a new tune, i guess my current tune was "on the edge" and that fmic sent me over the edge.. its just that i assumed more air flow meant more fuel, and i had to take fuel out to not hit fuel cut...

i looked at my 16psi log and timing dropped to 7 or so and steadily rose to 16 so i have a good starting point at 16psi... if i understand correctly timing drops at peak torque and then advances to 15+

i had to lean it out to get a better advance on my smic tune, and when i installed the fmic it overflowed and cut me off

or atleast this is the conclusion i came to comparing logs, but tonight will be a tuning adventure and ill post my final data log with IDC and IPW and give you guys more to critique me on thanks for the info guys

 

[ICE_T]

he's not suppose to past 105% of INJD,. with the 450cc and 190lhp.

maybe your injectors,. don't flow enought,.. clean it,. for about 100$,. the set.

 

[firebirdvert305]

Tell me the results....im going thru the same problem with my fwd 14b ...creeping to 20psi....kinda weird sh!t.

 

[blcknspo0ln]

if you're on stock fuel, and you're creeping to 20 psi.. then yes, most likely you are hitting major fuel cut

p.s., this thread is over half a year old

 

[firebirdvert305]

I know this thread is old... but i didnt wanna hear the people say "search" so i guess either way u lose...either u search and get called out or u dont search and get called out anywayz tho...i never had this problem before ...i made a new thread above....to tell my situation that happened...so weird tho...i still wanna hear what his results was...boost leak or major fuel cut?

 

[blcknspo0ln]

keep in mind a huge boost leak can cause fuel cut.. so the two go hand in hand. Especially if you're on stock fuel

 

[steve]

he's not suppose to past 105% of INJD

? Common wisdom is not to go over 85-90% IDC on injectors.

Steve

 

[Spookcorleone]

Ok so as some of you know I am runnning only a downpipe (until I can get a pipe/flange to reconnect everything, waiting on money so don't cry about the air I'm killing.) Recently my BOV has been sounding abit different, and once I get past 5K RPM's the boost goes from 14/15 PSI (which its set at) to a uncontrollable amount - until I get a nice fuel-cut or two. (If I lay off the gas abit and keep it from flying past 15PSI, it does fine.)

Am I getting creep just because I am only running a downpipe which enables it to just keep spooling more and more in general? or something else?

(I'm not leaking.)

 

[95blackGsTurbo]

That sounds like a wastegate problem. I've had boost creep but it usually comes back down. Doesn't go more than 2-3 psi above the set amount. What are you running for a MBC? Even with open downpipe, which I know a lot of people run, in 3rd gear or so you shouldn't keep creeping. Sounds like your wastegate isn't opening all the way and allowing more boost into the engine that it wants. I would check that first.

 

[Lunch_Box]

So let me get this straight you stomp on the gas and at 5000 RPM you get fuel cut and your boost gauge goes to 15 Psi? But if you feather the gas you can go past 5000 RPM and your boost doesn't stop building? This has nothing to do with your only running a down pipe, there is no performance dissadvantage to getting rid of your exhaust gasses early. Do you have a boost controller or anything?

 

[David15151]

yes that is boost creep. boost spike will return back down. boost creep just keeps going up. Basically there are a couple ways to fix this. More back pressure (restrictive exhaust). Or... Bigger interal wastegate like a 38mm. OR.. External wastegate. The for sure fix and most expensive would be the external wastegate. Basically your small internal wastegate is unable to keep up with the exhaust at this point.

 

[David15151]

So let me get this straight you stomp on the gas and at 5000 RPM you get fuel cut and your boost gauge goes to 15 Psi? But if you feather the gas you can go past 5000 RPM and your boost doesn't stop building? This has nothing to do with your only running a down pipe, there is no performance dissadvantage to getting rid of your exhaust gasses early. Do you have a boost controller or anything?

i think you may have read it wrong.. he is saying once he hits 5k at 15psi it will start to creep on him until it fuel cuts from the higher psi. If he drops the RPM once he gets at that point he is saying it wont fuel cut. Mainly because with the lower rpm there is less exhaust flow giving his wastegate a chance at dumping some excess boost .

 

[oldman]

Ok so as some of you know I am runnning only a downpipe (until I can get a pipe/flange to reconnect everything, waiting on money so don't cry about the air I'm killing.) Recently my BOV has been sounding abit different, and once I get past 5K RPM's the boost goes from 14/15 PSI (which its set at) to a uncontrollable amount - until I get a nice fuel-cut or two. (If I lay off the gas abit and keep it from flying past 15PSI, it does fine.)

Am I getting creep just because I am only running a downpipe which enables it to just keep spooling more and more in general? or something else?

(I'm not leaking.)

Does it pause at 15psi then slowly creeps up with rpm or does it shoot past 15psi immediately?

 

[Spookcorleone]

Damn you Oldman, now I have to ride in my car tomorrow and see. I goes up rather fast, once I get to 5000RPMs by the time I get to ALMOST 6000 I am running 18 - Can't really tell if its flying past 15 or not because it cuts out at 18ish - so I guess boost 'creep' would be naming it wrong...

It holds 15PSI from 1K-4.9Ish fine. Once I get past that it just starts boosting away.

Could the waste-gate actuator be messin' up? It was fine afew weeks ago (the boost that is.) Either way this is just what I "THINK" it does. Tomorrow I will attempt to pay closer attention (A.D.D.) and repost.

 

[oldman]

Damn you Oldman, now I have to ride in my car tomorrow and see. It holds 15PSI from 1K-4.9Ish fine. Once I get past that it just starts boosting away.

no need to test, you have boost creep. I hope you like porting, or put the rest of your exhaust back on.

Could the waste-gate actuator be messin' up? It was fine afew weeks ago (the boost that is.)

If you're 100% sure it was fine few weeks and that no work has been done since, A.D.D. , then it's definitely possible. Before you decide what next, apply compressed air to the actuator and make sure that the arm extends on time and all the way.

 

[Spookcorleone]

I enjoy porting, ported out a 2G manifold to put on the car, didn't understand why people complain about it until I saw how long it was going to take me just to get rid of that step... The exhaust will be going back on, and I will be getting another 14B turbo down the road (140K on current engine) so its only a matter of time before the turbo, or even the entire motor calls it quits. Should I port the o2 housing also - or will porting the wastegate area be good enough?

Ty like always Oldman.

 

[oldman]

Should I port the o2 housing also - or will porting the wastegate area be good enough?

Port everything, best free mod ever. The key though for boost creep lies in the turbine inlet.

Ty like always Oldman.

You're welcome.

 

[DSM BEEYACH]

This is just to inform anyone that decides to try port behind their flapper arm so that it can open 90 degrees to try fix their boost creep. Don't waste your time doing so unless you're upgrading to a bigger flapper. The wastegate actuator arm it self does not extend long enough to open the flapper full 90 degree's anyway. Like "OLDMAN" said "The key though for boost creep lies in the turbine inlet".

 

[oldman]

Spookcorleone: Just one more thing. Hitting fuel cut at 18psi with a 14b is an indication that you have boost leaks. Way too early.

 

[firebirdvert305]

Lemme know your experience with fuel cut.....What is it like....how did it occur...How did u eventually solve the problem? And how much did it scare the sh!t outta ya....

 

[racinmasonc]

feels like you just hit a brick wall.... hit it all the time in the cold here in Minnesota.. at 15psi...

 

[Insane4ceFed]

Im currently still trying to fix my fuel cut off. My car is 100% stock minus the forged internals that I have with a 20 overbore. I have NO boost controler and it runs 10psi wastegate on a 1st gen? Anyways I hit fuel cut off at 5500 and its like the car starves for fuel and cant climb the rpms anymore...also fallowed by a backfire once in a blue moon.

 

[oldman]

Im currently still trying to fix my fuel cut off. My car is 100% stock minus the forged internals that I have with a 20 overbore. I have NO boost controler and it runs 10psi wastegate on a 1st gen? Anyways I hit fuel cut off at 5500 and its like the car starves for fuel and cant climb the rpms anymore...also fallowed by a backfire once in a blue moon.

Boost leak test.

One time I hit fuel cut so hard that my car litterally shifted side ways, almost hitting the center divider. Took a while after that before I went WOT again. Guess what fixed it, boost leak test.