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

 

[crankbender]

theres a product out there by HKS its called a fuel cut defender its a computer doohikkie that just fools it into not cuttin fuel www.hksusa.com

do not remove fuel cut with the stock fuel system...you will break things.

Black smoke = extra fuel. This tells me that you are leaking counted air through a boost leak. Boost leak check your car and fix the problems. This leak will also cause you to hit fuel cut at 9 psi and nothing else mentioned would do the same.

 

[kpt4321]

You should not hit fuel cut until greater than 15 psi of boost, maybe 20. If you're cutting at 9 psi you have a big boost leak, guaranteed.

 

[blcknspo0ln]

affirmative. go to VFAQ.com if you're not familiar with making and testing for boost leaks. takes about 10 bucks and a half an hour of your time.

mine did the same thing, slow spool up and fuel cut at 12 psi.. then i discovered the 4" long slit in my hosing...

oh, and boosting past 13-14 psi on a stock fuel pump is the highest I would go. with a 190 I'd only go to 16 psi, which is what i'm at right now without any ill effects

 

[thefisl]

Ok, I got on the freeway and had to change lanes to get over onto the other freeway. It was very busy and I was getting close to the onramp, finally someone lets me by (one more lane to go). This lady was on her cell phone and either didnt notice me (which I doubt) or didnt care. Suffice to say she didnt let me through and I couldnt slow down enough so I missed the onramp. That B1@tch!! So I speed up so that I can at least flip her off, then I hear my turbo spoolin more than ever b4 ( I thought this was due to the new BOV) then, all of a sudden I hit what I perceived as fuel cut. I was at about 4Krpm and then the car seemed to stop as if I hit the brakes for a second. I let off the gas and then everything was fine. I didnt bother to catch up to her. But I had to make like a 5 mile loop to get going in the right direction.
So........I'm not sure if this is fuel cut or not, but the way I've heard it described, it seems like it. I know that I shouldn't be having this problem, b/c if you check my profile, I dont have sufficient mods to be at that point yet. All I have is a CAI, Greddy Type S (which I have connected both the nipples, the lower of which is T-ed into the line that goes from the turbo to the BCS). I know that I should have a boost gauge, but the other day I went to Autozone to get one and I asked the guy at the counter if they had any boost gauges and he said "What's a boobst gauge?" I was like WTF? This guy is retarded. Now I just got my ACT 2100 in right after I installed the BOV, so I never really got a chance to punch it. I think that I probably have a boost leak b/c I didn't have this problem with the stock BOV and I'm assuming that since the new one is holding more boost it caused a leak to open up or something. I want to get some opinions of what you guys think might be going on. I'm going to do a leak test but I don't have a boost gauge and in the vfaq it says to pressurize the system to something like 20 PSI and whatch the boost gauge to make sure you dont go over anything like that. What do you guys think? Please help.....

P.S.
sorry for the long post

 

[james13]

i had the very same problem...and my boost controller was unhooked so my turbo was over boosting. Check to see if you have both top and bottem lines hooked up on the boost controller.

-james

 

[boostedinaz]

You need to get a boost gauge. There is no way around it. Go to www.jegs.com or www.summitracing.com and look for autometer gauges. They will have the gauge to your door in a few days. From there drive the car and see what the gauge goes to. Its been along time since I have ridden in a stock 2G so I dont remember what the stock boost is. i want to say 9 lbs. If it creeps or has problems then you need to find them and fix it.

Pressure test the intake to make sure that you dont have a leak. I would test to 20 psi becasue that will eliminate all leaks.

Michael

 

[thefisl]

ok... installed boost gauge (splitfire [side note it came with a t fitting that had a restrictor on it...dont know if thats ok but installed it n e way.])

Max vacuum ~25
vacuum @ idle ~20
Max boost ~20PSI!!! ( I really dont know since thats where the boost gauge maxes out!!)

Also, my car was trailing white .....it used to just puff it whenever i revved but today when i started to test the boost gauge it was smoking slightly at idle.....when i came back it stopped..... Please help....

 

[boostedinaz]

Max boost ~20PSI!!! ( I really dont know since thats where the boost gauge maxes out!!)

There is you fuel cut right there. You are getting boost creep and need to figure out why and fix it.

Here is a qick search for yeah try these.
http://www.dsmtuners.com/forums/search.php?searchid=153162

Michael

 

[boostedinaz]

thanks.....that link you posted is a no go......

Weird.

Just type

boost creep

in the search and start reading.

Michael

 

[thefisl]

so mike you think its definitely boost creep? it couldnt be a boost leak? would a blown head gasket come in to play anywhere on this. ( i think my hg might be blown :thumbdown )

 

[boostedinaz]

so mike you think its definitely boost creep? it couldnt be a boost leak? would a blown head gasket come in to play anywhere on this. ( i think my hg might be blown :thumbdown )

It could be a boost leak but from my experiance it will just go to the boost you set it at, but since it is leaking the turbo will be working alot harder. So now that is is working so hard is has to pull in more air it will hit fuel cut.

Do a leak test and see what comes up. After that get a boost controller and try to bring you boost doen to about 15 lbs and see if it stays. If it does great if not then go after the boost creep issue.

There are a few ways to test for a blown head gasket.
When the car is cool turn it on and pull the radiator cap. You will see bubbles in it if it is blown.
You can also do the same thing and leave the cap on and if the upper hose is hard before the thermostat opens, then it si blown.
The last is to do a leak down test. You will see a high percentage of leak down in the cylinder that the gasket doesnt seal.

There are more but those are the easy ones.

Michael

 

[thefisl]

It could be a boost leak but from my experiance it will just go to the boost you set it at, but since it is leaking the turbo will be working alot harder. So now that is is working so hard is has to pull in more air it will hit fuel cut.

Do a leak test and see what comes up. After that get a boost controller and try to bring you boost doen to about 15 lbs and see if it stays. If it does great if not then go after the boost creep issue.

There are a few ways to test for a blown head gasket.
When the car is cool turn it on and pull the radiator cap. You will see bubbles in it if it is blown.
You can also do the same thing and leave the cap on and if the upper hose is hard before the thermostat opens, then it si blown.
The last is to do a leak down test. You will see a high percentage of leak down in the cylinder that the gasket doesnt seal.

There are more but those are the easy ones.

Michael

Ok, I checked the radiator cap......well I can't say I saw bubble persay.....it was like, well the only analogy that i can think of is this.....when you look at a river the water swirls around and creates very very very tiny bubbles........now I dont know if the cooland is supposed to just flow straight through or if it swirls around in there but thats exactly what it was doing...... can anybody go and look at theirs and describe what it looks like...... I can alwasy post a vid clip if thats possible....... Thanks guys.

 

[jdurston]

I am a DSM newbie, just picked up a 92 fwd turbo last week.

I think I am experiencing fuel cut. The boost does not seem to build very well at low rpms. At high rpms it really pulls but it always cuts out a bit past 6000 rpm. I don't have a decent boost gauge yet, but the stock gauge reads close to 1 kg/cm2 at high rpms, max throttle.
The wastegate actuator arm fell off the wastegate arm. I put it back on. (I think the original owner didn't tell me something.)
I can move the actuator rod but it takes considerable force. The wastegate arm moves fairly easily. Is there an easy way to check the actuator. Right now I am not driving the car. I don't want to blow my engine from overboosting.
I'll probably just try and get a used actuator from a junkyard if my original one is bad. What kind of pressure should I be seeing once I install my autometer boost gauge?

Thanks in advance.

Josh

 

[SlowSpyder]

if the pressure source is connected straight to the actuator then you should see about 7-9 psi

 

[98GSX-WI]

The majority of my mods are now installed (see profile)....the last mod I am having done for what I'm calling MY Stage 1 is the bigger fuel pump, regulator, gauge... When first increasing the boost, I eventually got to about 17-18 psi and then I got fuel cut (my intention wasn't to go that high, but seems good to find out when fuel cut would occur). Anyway, I backed it down to about 14-15 psi and it's running good. Question is, with a 255hp fuel pump, will this allow me to increase boost to 17-18psi--without fuel cut? The more I think about it, won't the bigger fuel pump just allow me to increase the boost without going to lean....if I get fuel cut before the bigger pump, won't I also get fuel cut at the higher boost after the bigger pump? I'm curious, because I read that fuel cut is only related to the air flow the MAS senses and that the ECU ultimately calculates based on the Hz, pressure, and temp. Thanks in advance. I'm finding upgrading this car very interesting, especially understanding exactly how everything works (in theory) and why certain things happen....

 

[ho bag]

fuel system upgrades like fuel pump and regulator dont matter to fuel cut, cut is related to air flow.

To move fuel cut you need to chaneg the amount of air the engine sees but then u run lean, thats why you need bigger injectors to compensate for it. if you wanna rais fuel cut buy some 550's and afc or maft

 

[temfate]

Furthermore, the "pressure" you can run without hitting fuel cut will vary. Pressure is just that, pressure. It's not a relation at all to air volume which is what matters. With the stock turbo you could push 16-17 psi without worry, but with a big16g or larger you'd have to worry going over 15psi (or less with bigger ones). The amount of air the turbos flow is measured in CFM, and that's what the ECU sees.

 

[98GSX-WI]

Thanks guys. That is what I suspected. I have a ported Big28 turbo, but I'm not quite sure how much air it flows. I saw a list with with different turbos and how much they flow, but the Big28 was not on the list. Does anyone know how much it flows. I have an EVO III manifold and O2 housing with a full 3" exhaust. The Big28 should be flowing pretty good.

 

[philipkrotch]

it all depends, ive run 20+ psi on my stock MAF hacked and no fuel cut, my friends GVR4 would hit fuel cut at 16 with the stock maf hacked.

 

[hendy81]

After hundreds of dollars spent at the shop to try pin-pointing this problem, nothing has been done about it. In any gear, at any boost setting (I use a Turbosmart dual stage boost controller w/rocket switch) my car leans out hard between 5000-7000 rpm. It feels like fuel cut and hits hard enough that it feels like I'm gonna take a trip through the windshield. My air/fuel guage stays in "rich" until this happens when it nosedives into "lean". Any ideas?

To try to combat this problem (as well as add a little power) I have switched to a higher output fuel pump, adjustable fuel pressure regulator w/guage, modified fuel rail, new O2 sensor (about 3 of them) but nothing has worked. The mechanics even datalogged it and the only problem it could find was my O2 sensor.

Any help would be greatly appreciated.

Hendy.

 

[blitz43]

After hundreds of dollars spent at the shop to try pin-pointing this problem, nothing has been done about it. In any gear, at any boost setting (I use a Turbosmart dual stage boost controller w/rocket switch) my car leans out hard between 5000-7000 rpm. It feels like fuel cut and hits hard enough that it feels like I'm gonna take a trip through the windshield. My air/fuel guage stays in "rich" until this happens when it nosedives into "lean". Any ideas?

To try to combat this problem (as well as add a little power) I have switched to a higher output fuel pump, adjustable fuel pressure regulator w/guage, modified fuel rail, new O2 sensor (about 3 of them) but nothing has worked. The mechanics even datalogged it and the only problem it could find was my O2 sensor.

Any help would be greatly appreciated.

Hendy.

my friend had a really bad fuel cut problem and it felt like it was going to hit a brick wall
in his words....

what he did was replace the spark plugs with NGK br7ses i think thats how you spell it but anyways its the 7 series ngk plugs and it got rid of his fuel cut prob and drives like a new car...i changed mine to just to be on the safe side....

and i don't think the data logge or obd2 or what ever would tell that plugs are going or are bad...

but before you spend thousands of dollars in inspection and replacing things that does not need to be replace try the plugs.. they are about $2.50 each...inexpensive upgrade if you ask me...

let me know if this works 4 ya....

 

[hendy81]

Apparently they did change my plugs as well, but the problem didn't change at all. I'm not sure exactly what kind they put in yet, but it's what they use in their race Talon. Also, my plug wires have been replaced with MSD 8.5mm wires. Could it be a timing problem?

 

[MrdB]

my car would do the same thing, i took off my greddy BOV and it was fine.. slapped my 1g back on.. golden

 

[brian524]

Spark Plug gap could be a key issue. Pull them and make sure 1. there all gapped the EXACT same and 2. that there gapped .028, or somwhere very close to that. Im pretty sure your shop would check this though.

Also turbo info and fuel injector info would help in pinpointing a problem. You very well could be leaning out up top, but again im sure you know your shit and arent underfueling a big turbo or something of that nature.

Anyways, good luck with finding your problem

 

[Luv2Spool]

not sure what type of A/F gauge you have but I would suggest switching to an EGT gauge for a more accurate idea of how rich or lean you are running and an SAFC would be a wise investment. Also, I had a similar problem and found that one of my IC pipes was loose and my engine was basically choking to death. Other things to check would be are you venting your BOV atmospherically or are you recirculating (venting atmospherically makes your car run rather rich)? How cold is it outside when this happens (cold air=more dense= fuel cut). Just my 2 cents, good luck with the problem.