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

 

[HotSauce GS N/T]

i always put in 93

 

[speedracer91]

it feels like your tranny just fell off and u ran over it....and then u look in the rear view to check

 

[oldman]

I read in one of the posts that if you hit fuel cut, you must pull the negative terminal to reset the ECU. Why? What ill effects if you don't? Thanks.

 

[flytalon93]

I believe you have to do that because the ECU stays in a "SafeMode". From what I have read here, if you don't reset it, the ECU becomes very sensitive in this mode and you will hit fuel cut more often.

 

[99evo3gsx]

is it still hitting fuel cut in warmer weather? maybe you have a boost leak...does the turbo spool completely? does it feel any slower? are you running richer?

 

[xcelr8n]

the fmic has everything to do with this, youre flowing more air now, the ecu is seeing more air and cutting fuel. adding fuel wont help persay, you need to trick the ecu into seeing less air, ie. piggyback

 

[dsm4life]

it feels like this

verrrrrrrooooooooooooooooooooooooooommmmmmmmmmm blub blub pop blubbb followed by disappointment

 

[mnexcited]

You will normally get fuel cut at 17 with stock fuel system.

 

[xcelr8n]

ya chances are good you have an intake leak, and the maf is reading more air trying to compensate, and bam fuel cut.

 

[Jeffrow95]

Just recently raised my boost up to 20 psi and started to get fuel cut, so i bought a 255 Walbro fuel pump and installed it. Came to find out i had a boost leak. So i got that fixed. Now i cranked the boost up to 23 psi and i began to get fuel cut again. What a Big headache. Can't think of anything else that could be wrong with it. Any advice will help.

 

[NOSLO2PT0]

Fuel cut has NOTHING to do with the amount of fuel you are giving the engine. It's all based upon airflow, barometric pressure, and air temps. The ECU has NO idea what size fuel pump or injectors you have. It could care less. All it cares about it is AIRFLOW. Turn your boost down. You are probably trying to run 23psi on pump gas anyway.

 

[Jeffrow95]

Rechecked everything over again and found out that the rubber seal that goes around the top of the fuel pump outlet was to big and was really loose letting fuel leak around back down into the tank. replaced rubber seal and no more leakage, and has more fuel pressure. Able to run 23 psi without any problems now.

 

[leakyfaucet]

Yeah the ECU reads airflow for simple fact to help keep A/F ratio the same but with fuel pump upgrade should allow you to push more boost to the engine even up to 25 psi.

Yeah, but without messing with what airflow the ECU sees, you're still going to hit fuel cut.

If you were having problems, and a rubber seal fixed it, it sure as hell wasn't fuel cut.

Also, I'd like to add that NOSLO2PT0 does know what he's talking about. It is you who doesn't.

 

[Defiant]

Buddy, i don't think you have a clue. Fuel cut does have something to do with it. Yeah the ECU reads airflow for simple fact to help keep A/F ratio the same but with fuel pump upgrade should allow you to push more boost to the engine even up to 25 psi. And yeah i ran 23 psi on 93 octane and know people that run 26 psi on pump gas with no problems so whats your point?

http://www.tmo.com/faq/diagport/970929.htm

"There are three conditions under which the DSM ECU will chop fuel.

1. Engine speed higher than 7500 RPM. This is overrev protection. If your engine rotates faster than the valve springs can pull the valves back up into the head, the pistons could smack into them, causing major damage. Note that simply chopping fuel will not stop the overrev condition if you misshift and the transmission rotates the engine past the revlimit. (The author did this to his friend's M3.)

2. Engine air flow greater than a certain amount. If the airflow into the becomes too great, the phenomenon by which the MAF counts the air entering the engine starts to break down, missing counts. The factory ECU sets a very conservative limit here. It doesn't need to be as conservative as it is to prevent missing counts. After we removed this limit, we were only able to hit the MAF counting breakdown problem on a first generation DSM with a 20G set to 19 psi on a 3" exhaust.

3. Engine under high vacuum for more than a couple seconds. This is not a matter of engine safety, but of smog control. Some of the worst smog can occur during engine deceleration. If you are coasting down a steep hill using the engine to help slow you, the ECU will turn off all fuel to the engine to both aid in engine braking and smog production."

http://members.shaw.ca/costall/ECUprimer/ECU_ch7.html

 

[GSX503]

Rechecked everything over again and found out that the rubber seal that goes around the top of the fuel pump outlet was to big and was really loose letting fuel leak around back down into the tank. replaced rubber seal and no more leakage, and has more fuel pressure. Able to run 23 psi without any problems now.

What rubber piece are you talking about, I would want to know. I'm hitting fuel cut at 18psi with 255 walbro. My pump seems to work abit better than stock, no clue. Its rewire, but isn't it suppose to be noisy, cus I don't here much noise from it. Im also running a T3/T4 3" inlet and 2.5 outlet.

 

[NOSLO2PT0]

Buddy, i don't think you have a clue. Fuel cut does have something to do with it. Yeah the ECU reads airflow for simple fact to help keep A/F ratio the same but with fuel pump upgrade should allow you to push more boost to the engine even up to 25 psi. And yeah i ran 23 psi on 93 octane and know people that run 26 psi on pump gas with no problems so whats your point?

You can stick a 500lph fuel pump in the car and still hit fuel cut. Lots of people in here install Walbro 255's and they still get fuel cut. As far as you running 23psi on pump gas, so what? Doesn't mean you are making any power. Oh, and I'm one of those guys running 26psi on pump gas, so that IS my point

It's not so much what you have claimed to be able to do as far as running xx psi on yy octane, it's about being able to put up some measurable #'s backing up those claims. What good is running 23psi on 93 octane if you are knocking all over the place, making a whopping 300whp, or running mid 13's? I'm not saying you are doing any of these, but at least consider what you say to WHO you say, before you say it. I've gone faster on pump gas than you prolly ever will go on race gas

Oh, and the reason you can now run 23psi safely AFTER you fixed the leak is.. you probably had to run the car a bit richer to make up for that loss of fuel pressure. More fuel pressure = more fuel = need to make ecu see less airflow. Less airflow = less chance of fuel cut. Still nothing to do with actual delivery of fuel by the ECU.

happy boosting

 

[NOSLO2PT0]

What rubber piece are you talking about, I would want to know. I'm hitting fuel cut at 18psi with 255 walbro. My pump seems to work abit better than stock, no clue. Its rewire, but isn't it suppose to be noisy, cus I don't here much noise from it. Im also running a T3/T4 3" inlet and 2.5 outlet.

What size t3/t4? What size injectors? If you want to get rid of your fuel cut, you can crank up the base fuel pressure and lean the car out via AFC. Or buy bigger injectors and lean it out more. Or, fix all the boost leaks you have, which is a BIG cause of fuel cut. You might be putting out 25psi of air at the turbo, but by the time it gets to the motor, might only be 18psi. ECU sees 25psi of air, not the 18psi reading at the gauge. Keep in mind, it doesn't know quantitatively the amt. of air coming in, it just knows volume of air, temps, and baro. pressure. You'd be surprised how much more boost you are running once all of your leaks are fixed. This alone will allow you to turn the boost down.

 

[GSX503]

What size t3/t4? What size injectors? If you want to get rid of your fuel cut, you can crank up the base fuel pressure and lean the car out via AFC. Or buy bigger injectors and lean it out more. Or, fix all the boost leaks you have, which is a BIG cause of fuel cut. You might be putting out 25psi of air at the turbo, but by the time it gets to the motor, might only be 18psi. ECU sees 25psi of air, not the 18psi reading at the gauge. Keep in mind, it doesn't know quantitatively the amt. of air coming in, it just knows volume of air, temps, and baro. pressure. You'd be surprised how much more boost you are running once all of your leaks are fixed. This alone will allow you to turn the boost down.

I'm new to dsm, what is a base fuel pressure. Im still at stock injectors and will soon to pick one up this comming Jan. Hey whats better for me, I have 250 to spend, injectors or SAFC? I ask the shop to put in a 16g and when I went to pick up my car, they put in a porte t3/t4 Airesearch TO4 with 3" inlet and 2.5 outlet, said support 400hp+ and is better and bigger than 16g or evo 16g. I only want to run about 270hp at wheel only or 19psi.

 

[dave99gst]

I'm new to dsm, what is a base fuel pressure. Im still at stock injectors and will soon to pick one up this comming Jan. Hey whats better for me, I have 250 to spend, injectors or SAFC? I ask the shop to put in a 16g and when I went to pick up my car, they put in a porte t3/t4 Airesearch TO4 with 3" inlet and 2.5 outlet, said support 400hp+ and is better and bigger than 16g or evo 16g. I only want to run about 270hp at wheel only or 19psi.

are you asking what is base f/p or what should it be set at ?


its going to take alot more then $250 to get 270whp

 

[Generation1JeY]

alright guys i have a weird problem with my car. Ever since i got my 3" exhaust i have been slowly getting this problem with my high rpms. This is what happens: i floor it, turbo spools up perfectly, once it hits full boost (15 psi) and hits 4k rpm, the engine just starts gurgling like its backfiring or fuel cutting or misfiring. I wish i could explain the noise more, but all i can tell u is that like the engine just DOESNT want to rev any higher, like when it happens even if i keep it floored it just like stays near 4k and doesnt accelerate anymore.

I turned my boost down all the way to 9 psi and then i didnt hit it at all, all the way to redline i had full power with no backfire, no fuel cut, nothing. Then i slowly started to increase it, near about 12 or 13 psi it started doing it again at about 5k rpm.

A few people suggested dirty injectors, i put a full bottle of injector cleaner in at my last fill up and it hasnt changed anything as far as i can tell.

I'm starting to lean towards electrical problem, plugs, wires, coil, ignition. Something like that, but what i dont understand is how it can just start up all of a sudden, like right when i bought the car and it had a broken wastegate, i could spool the turbo to 20 psi and not have any problems at all, now it just starts freaking out at only 13 psi.

Help Please!

 

[Catbox_95]

The EXACT thing happened to me when I installed my full 3" exhaust. I mean, it never happened, then I drove to the shop and had the exhaust installed, then immediately afterwards it did just as you described.

What I did-

First I put a bigger fuel pump in it (Walbro 255 lph). That helped, but it still did it, just at a higher rpm. Then I installed an S-AFC 2 and with proper tuning of air/fuel mixture, it went away. I could pull to 7,000 rpm under 15 psi, no problem (I have the stock turbo).

But then again, you might not want to listen to me too closely. After one day of tuning with the S-AFC, my car is in the garage getting the head pulled because I lost compression in cylinder #4!

 

[Talonracer06]

this is my understanding of fuel cut....has some but not much of anything to do with the pump, yeanh it makes a difference but its more of an ECU thing....the computer read the rpms and kicks in as a safety ..the only way to really bypass that would be an AFC or other stand alone fuel management...the Apexi AFC unit will bypass the fuel cut and speed limiter...this is the key to getting around it...just go by a afc for 250 beans and call it a day....you guys really need to chill out on these threads too ......relax.....happy boostin...

 

[Hal]

It's called FUEL CUT because the ecu CUTS OFF THE FUEL when the airflow amount exceeds a predetermined level for the current throttle and rpm levels.

It has NOTHING to do with the ANY PART OF THE FUEL SYSTEM.

Hal

- we now return you to your regularly scheduled broadcast of mis-information

 

[GSX503]

so guys, I living on a small budget. So what is better for my set up for now. AFC or 550cc injectors. Which will make my car run little smoother than smelling like raw gas.

set is:
ported T3/T4 3"inlet 2.5 outlet
3"downpipe and exhaust
ported o2 housing
intake and others
255walbro

Running super rich right now at last green of a/f ratio.

 

[NOSLO2PT0]

so guys, I living on a small budget. So what is better for my set up for now. AFC or 550cc injectors. Which will make my car run little smoother than smelling like raw gas.

set is:
ported T3/T4 3"inlet 2.5 outlet
3"downpipe and exhaust
ported o2 housing
intake and others
255walbro

Running super rich right now at last green of a/f ratio.

Get the AFC. You can prolly lean the car out a little due to the extra fuel supplied by the 255. The 550's will just make your car run even richer.