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

 

[punishercb]

1.) It's very difficult, and remarkably brainless to look for full-boost in first gear. The pistons get away from the boost too easily because first gear isn't enough load on the engine.
2.) Fuel cut is a function of airflow, and has no relation to boost levels. When the engine sees too much air coming in, it determines that something is wrong and that it's probably the turbocharger running wild. In a desperate attempt to keep the pistons below the head casting, it chops off the fuel supply.

Don't even try to boost in first gear. Use first just to get the car into second.

Thanks for the explanation defiant, that really makes sense. I try and explain fuel cut to my buddies and always have a hard time. Now I can do a better job.

 

[oldman]

Also, 17psi on 14b with stock fuel system may be pushing it considering you still have some boost leak. Turn it down a little and see if it helps. Are you creeping with the 3" exhaust?

 

[BOOSTn20psi]

I have a Garrett Hybrid turbo that I'm running with stock fuel injectors and a stock fuel pump. I recently raised the boost from 10psi to 15psi with my SB MBC and now when i hit the gas in 1st the gauge only goes to about 10psi thats flooring it, when i shift the car into 2nd slowly (normal) the car boosts to 15psi just fine, same with 3rd and 4th but when the car is at high RPM say 4000 then i floor it the boost gauge does not go past 8psi. (Thats in 2nd,3rd,4th,5th) The car feels like it just hits a wall. Could this be fuel cut off? I dont know what it could be a boost leak maybe? I just bought a walbro 190 fuel pump should i try that bigger fuel injectors? Any info would be great! Thanks Guys

Hey, my car was doing the same as yours too, but I fix it. My T3/T4 is pretty big and it will make my car run really rich.
Does your car smell like gas? Cause my car smelled like raw gas and so I found a Boost leak at the mani, which causes the gage to read very low but ecu reads high. Say I set my MBC to 15 psi and hits fuel cut, cuz it probably reads like 20+ at ECU do to the leak.
If this greddy is the 18g you'll end up spend $$$$$. I spend close to $1K in less than a week for fuel system upgrade, and with all that stills hit fuel cut until you get to dyno.
Don't blow your motor, WARNING.

 

[punishercb]

Also, 17psi on 14b with stock fuel system may be pushing it considering you still have some boost leak. Turn it down a little and see if it helps. Are you creeping with the 3" exhaust?

No, actually my boost is going down. ALOT. When I run full boost it raises to about 17 psi and then creeps down to about 12-13 psi as the engine runs faster. Around 3000 rpm it's at 17 psi and by 5500 it's at 12-13.

I'm going to try and rebuilt my t.b. this weekend along with my passenger wheel bearing and speedo Thanks for the part number.

 

[oldman]

I'm going to try and rebuilt my t.b. this weekend along with my passenger wheel bearing and speedo Thanks for the part number.

After you fix the leak, turn the Hallman all the way in and disconnect the hose from the actuator and test run with the nipple open. This will result in all out boost (well hopefully) so feather the throttle to maintain 16psi. If problem solved, mbc or the hose to actuator is in question. If problem persists, either flapper is not completely shut or turbo is in question. I'm taking about boost dropping off.

 

[punishercb]

Okey dokey, I'll try what you said. Hopefully I'll get to it all because I just found out my grandparents are staying for the weekend... (which means all attention on them)

We'll see, gotta keep my hopes up.

 

[BLampinen]

Ok, i dont know if these problems are related or not, but they both started at about the same time. First, i'm running a little rich, but i dont know how rich, because the datalogger says im dead in range. but, you can smell the gas in the exhaust and it loves to backfire lately, as well as bogging down. also, when its cold, it hits fuel cut at WOT around 5000 rpm. i'm only running around 13 psi of boost, so why would it fuel cut??

 

[ddavisaf]

Stock injectors, stock pump?
How are your plugs looking?

 

[BLampinen]

yeah i shoulda specified... 255 lph walbro and 550 cc injectors. plugs look brand @$$ new

 

[killakev805]

yeah i shoulda specified... 255 lph walbro and 550 cc injectors. plugs look brand @$$ new

Do you have an afpr? You will need on with a Walbro255

 

[BLampinen]

i honestly dont know. i bought the car prety much as is and never got a complete list of mod's from the previous owner. but i've had the car for about 8 weeks now and its just recently doing this. so im assuming if an afpr is necessary, i must have one...

 

[killakev805]

i honestly dont know. i bought the car prety much as is and never got a complete list of mod's from the previous owner. but i've had the car for about 8 weeks now and its just recently doing this. so im assuming if an afpr is necessary, i must have one...

now don't hold me to this, because I am just going from what I have heard. If you don't have an afpr, and you have a 255, then it will pump too much gas, which could cause a rich condition. You need a way to regulate the pressure going to the injectors. I would check to see if you have one.

Other than that, how are you controlling the fuel injectors? S-AFC?

 

[BLampinen]

no, thats one thing i need to fix.. i have no fuel management at all other than my stock mas and my o2 sensor. im hoping to get an EPROM and DSMLink in the next month or so tho

 

[ddavisaf]

killakev805 Hit the nail on the head

 

[killakev805]

no, thats one thing i need to fix.. i have no fuel management at all other than my stock mas and my o2 sensor. im hoping to get an EPROM and DSMLink in the next month or so tho

That is why you are running rich and hitting fuel cut. If you run bigger injectors on just your stock ecu, then it will trigger them just like they were your stock injectors, so you are pumping too much fuel into the cylinders, causing it to run rich. Once you get something to control your fuel, and a afpr you should be able to tune it.

 

[oldman]

Fuel cut is triggered by air flow, very little to do with the fuel system. You're running pig rich because of several reasons, two of which have been stated above, 550 without any tuning device and the lack of afpr. However, if you're truly hitting fuel cut, you probably have some serious boost leaks.

 

[BLampinen]

hmm, i was actually wondering about boost leaks myself, im going to definetely have to check that out... cuz i know i have an exhaust leak somewhere in the manifold or down pipe and i think ive got a boost leak somewhere too... but do i need an afpr and fuel management? wouldnt dsmlink be sufficient for both?

 

[oldman]

but do i need an afpr and fuel management? wouldnt dsmlink be sufficient for both?

dsmlink will take care of the injectors but not a fpr overrun because an overrun is a non-linear change which can not be tuned out, you can come close but not completely. Do a research on "afpr" and "overrun", read up as much as you can and post back well informed questions here if you have any.

 

[JoeyJigglesGSX]

real quick: eIII16g, 255lph, MSD wires, NGK 7, intake, greddy type-s, 2.5" to the flex, 3" back and 3" high flow cat.

just found out my electronic boost gauge has been broken and lieing to me forever. When i thought i was at 17psi i was really at like 8. Anyway, so i get a mechanical boost gauge and i turn it up to 14psi and i think i hit fuel cut? how can this be? i never had this problem when i was at 10psi.

this is what happened because i refuse to do it again. Got on it in second gear, was screaming up in RPMs and then bam! car jerked and a lout backfire... i prob. could have kept accelerating but i didn't because im sure it would have just did it again.

i know i have to do a leak test, but if i had a leak i would think it would have hit fuel cut at 10psi...i could be wrong

Please help

 

[ddavisaf]

First. you're running a 255 without fuel management and injectors.............................


Wake up and smell the gasoline...

You need to take that out, install the stock fuel pump and wait until you buy dsmlink and injectors and a fpr

 

[DGajre777]

Your mods list from your profile:
Ported EVO III 16g, ported o2 housing, 2.5" downpipe, 3" exhaust w/ 3" high flow cat, 255 lph Walbro Fuel Pump, Injen Intake w/ Extreme Motorsports filter, Dejon Tool Upper & Lower intercooler pipes, Greddy Type S BOV, Hallman Pro Boost Controller, Autometer C2 Boost & A/F Gauges, Greddy Full Turbo Timer, MSD Wires, NGK 7s Spark Plugs and Aftermarket reverse glow gauges

1) You NEED a AFPR for that 255. If you didn't want to get a AFPR, you should have gone with a 190 pump for that evoIII turbo.

2) Do NOT increase boost without fuel mods. A pump alone is not a fuel mod, you NEED injectors, AFPR (for the 255 only), injectors and some way to control the injectors (SAFC or MAFT or DSMlink).

3) As for your options:
- Take out the 255 and put in the stock pump
- Take out the 255 and buy a 190
- Leave the 255 on there and buy a AFPR

After you buy injectors, SAFC or MAFT or DSMlink - turn the boost up.

Everyone on here is probably going to tell you the same thing that 'ddavisaf' and I did.

 

[oddrob]

If the ECU thinks its seeing too much boost, it will fuel cut, It didn't do it at 10 because that was below the threshold, 14, for whatever reason is over that threshhold.

 

[tinyturbine]

Take out the injectors, simple as that. 550s with no compensation??

 

[ddavisaf]

He's got a pump, just no way to control the flow. Keep the injectors and buy dsmlink

 

[JoeyJigglesGSX]

If the ECU thinks its seeing too much boost, it will fuel cut, It didn't do it at 10 because that was below the threshold, 14, for whatever reason is over that threshhold.

so then with an AFPR can i get over that threshold?

and with an AFPR how do i know what to do?