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

 

[hose101772]

Gap your plugs down to .028" or less,if .028 gap still does it,go lower.I have to run mine at .025 to .020-depending on outside temps.

 

[Powerboarder]

Here is what I found when I checked the gap!!! Iridium plugs lasted 2 months!!! LEAN?

 

[IHeartTurbo]

ive been getting fuel cut at 5000 rpms ever since i got my car. i was recently told that it is because i have a boost leak around the intercooler inlet and that i should replace it. does this make sense because i dont want to get a new smic if i dont have to. mods are s16g, 2.5"catback, mbc, free mods for reference

 

[hose101772]

You might try some standard ngks next time.Never used iridium but I've had good luck with bpr7es's gapped short.

 

[a351must2]

Now that's some scary damage...definately lean.

I didn't realize the Iridium plugs had the tiny tips like Platinum plugs...definately a bad thing. The small tips get hot and promote detonation.

 

[95JDMTSI]

yea got it.... anyway about this fuel cut thing... im pretty sure all my clamps etc are tight but the tb feels tight. i think the IM is stripped about 3/4 a cm inside at the tip where the end of the bolt screws in. is there naything else it could be besides this screw that won't tighten? do i have to take off the IM and retap it? can i use some thread lock stuff? please help me stop the fuel cut.. it wasn't doing it before i tried to take off the tb elbow and apparently stripped the IM but it could be the cold or something.... also will i fix it by hacking the mas?

 

[AwdEi]

You should go ahead and install it so you can add more fuel so it doesnt cut. If it still cuts, just turn the boost down some and tune at whatever psi.

I'm not too sure about turning off the fuel cut. I know you can with types of fuel management, but I dont know about stock.

 

[ivanr4g63]

Did you hacked your mass...? at least the lower honeycomb...
You'll probably need bigger injectors sometime soon.

 

[PowerEclipses]

just a question, what would hacking the lower honey comb do? bigger injectors on stock turbo ? we have pretty big injectors stock and people even run 16gs with them
Anyone think it might be a FPR? That i'm not keeping a constant pressure to the rail?

 

[Clipse90Turbo]

Thanks a lot. the only bad thing is at the track my tansmission blew...You wouldn't know or have any connections on getting a tranny??? That would be nice!


Chris

 

[Benji]

First of all, you have really got to understand 'Fuel Cut'.

The ECU cuts fuel when the airflow exceeds a certain amount. Now, this is with the final calculated airflow, not just the Hz signal, which means that temperature and barometeric pressure will effect fuel cut as well. This airflow number is based off of the maximum amount of fuel that the stock fuel pump and injectors could deliver to the engine cylinders and is hardcoded in the ECU.

It does not matter how much Fuel you actually feed the engine. The programmed ECU does not know what has been changed. It still knows though that if x amount of airflow is seen, I will cut fuel and engine spark.

What's the solution to this? You have to fool the ECU into believing there is less air entering the engine than, in fact, there is. This can be done altering one or more of the input signals sent to the ECU by the various air measurement sensors present in the MAS. That's what a VPC, AFR, AFC, MAF-T, etc ... will do.

 

[92turbors]

If the computer saw the injector pulse width too high would it do anything? My car hits fuel cut but it is stock w/ hacked maf. Is it air volume at a certain RPM it looks at or just on specific air volume number? My fuel cut hits at various air volume number from 4 - 8 (on my pocket logger) Maybe I'm not hitting fuel cut, but it sure feels like it. And I can hear the fuel relay click off/on when it happens.

 

[FASTSPOOLINGST]

http://www.dsmtuners.com/tuning-guide/2gturbo/stage1power.php

REF: STEP 10

http://www.dsmtuners.com/tuning-guide/2gturbo/stage2power.php

REF: STEP 4

 

[FASTSPOOLINGST]

How do I prevent fuel cut?
I have [injectors/fuel pump/fuel rail] installed, but I still get fuel cut! Is there a fix?
Search for this topic now!

This question comes up a lot, mostly because people misunderstand what fuel cut is for, and why it occurs at all. For the answer to this, read this chapter of the ECU Primer.

The simple answer is that because fuel cut is pre-programmed into the ECU, there is no method of disabling it. There are no modifications that can do so, aside from an ECU upgrade that eliminates fuel cut. Upgraded fuel pumps, injectors, and fuel pressure regulators do nothing to avoid or eliminate fuel cut. NOTHING.

That being said, there are some methods (some cheap, some not) of postponing fuel cut. All the methods work on one principle: fooling the ECU into thinking there is less air entering the engine than, in fact, there is. This can be done by adding unmetered air, or by changing the sensor inputs used by the ECU to determine air mass. Of course, these methods usually mean the engines run leaner than stock. Again, read this section of the ECU primer for details.

Methods include:

removing the lower honeycomb from the MAS. See the FAQ Locator (look in the "Intake" section) and Jim McKenna's MAS modification page for more information.
'Gutting' (cutting out) the lower section of the MAS. This modification was first marketed by HKS, improved upon by Roger Hanson, Eric Typpo and Jim McKenna, and recently re-popularized by Al Blaha. This involves cutting out the entire lower section of the MAS - delaying fuel cut, but making the engine run leaner - and altering the intake air temperature sensor to compensate. Mike Jackson also does this - read his information here.
plumbing in a secondary air intake after the MAS. Use extreme caution!
the fuel cut defenser (FCD) by HKS
the dime-store fuel cut defenser (DSFCD) for 1G or 2G. Use appropriate caution.
fuel management computers, like a VPC or PMS. See the Glossary for details.
An ECU upgrade from Technomotive is the only way to really eliminate fuel cut

 

[FASTSPOOLINGST]

What is fuel cut?
Search for this topic now!

Fuel cut is cessation of fuel delivery and spark generation by the ECU. It is a pre-programmed response designed to save the turbocharger from utter destruction in the event of a catastrophic wastegate malfunction. For more details, read the ECU Primer, specifically the chapter on fuel cut. Also read Todd Day's Diagnostic Port issue on fuel cut, and the answer to "How do I prevent fuel cut" in this FAQ.

 

[FASTSPOOLINGST]

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

another link to fuel cut...

P.S.

Buy a Stage 3 Eprom chip

 

[92turbors]

I have seen all of those articles and been reading post after post about fuel cut but I have never heard at what air volume fuel cut happens at. Nore if the hard coded volume numbers are in relation to RPMs. I think the reason this topic is beaten to death is because it makes the DSM no fun to drive when you have to shift at 5000 rpms. Especially when it is a stock one

 

[Dieselboy]

I believe fuel cut happens on 1G's at 2600hz. 2G's Im unsure but its far more.

 

[92turbors]

Now 2600 hz would be air flow, isn't that when the signal gets distorted (MAF Overrun)? The fuel cut is from Air Volume right? On my logger that is a low number from 0 to 8 or so. What is the max value the air volume can be before fuel cut? I know my hz never gets close to 2600 it just hits 1606 when the fuel cut hits. Sorry to interupt the argument guys. Keep it up it's funny.

 

[KidintheTSi]

I have a quarter mile time somewhere? didn't even know it. What is it? The only time i've ran the car at the track was right when i got it, found many things that the person before me had wrong since. But wow, you really are a big man aren't you? You amaze me...can we all say "insecurity"? You know what-YOU have a nice day, thanks for brightening mine, got a good laugh.

By the way; why the hell can't you manage to say anything in ONE post, why must you always make about 14?

 

[KidintheTSi]

92turbors:

I think i read somewhere that 1606hz is the highest it will read or something, that you're actually moving more air than that, that the ECU or something doesn't account for it. I dont remember exactly what i read about this, i'll try to find it again. If I do i'll post it for ya. For some reason, that number sound familiar tho...

 

[92turbors]

Yes 1606 is the highest the logging software can see but the curve is moving up at steady rate and right when it reaches 1606 it hits fuel cut. So I am almost certain it doesn't go from 1580 to 2600 hz in 1/12th of a second. I was just wondering if anyone with a logger and a 1G knew what air flow value the ECU will allow befor fuel cut. My car has run like sh!t since I bought it so I don't know what a normal running cars log would look like. What is the injector pulse width when your full throttle around 5K? Mine is in the 20's which according to the logger way over 100% duty cycle. Maybe my injectors are crapping out on me at the higher rpms. Thanks for your help.

 

[Dieselboy]

Originally posted by 92turbors
Yes 1606 is the highest the logging software can see but the curve is moving up at steady rate and right when it reaches 1606 it hits fuel cut. So I am almost certain it doesn't go from 1580 to 2600 hz in 1/12th of a second. I was just wondering if anyone with a logger and a 1G knew what air flow value the ECU will allow befor fuel cut. My car has run like sh!t since I bought it so I don't know what a normal running cars log would look like. What is the injector pulse width when your full throttle around 5K? Mine is in the 20's which according to the logger way over 100% duty cycle. Maybe my injectors are crapping out on me at the higher rpms. Thanks for your help.

Ive had my logger a short ammount of time. Ive spend most of it keeping track of knock, timing, O2, and temps...not so much air flow

 

[92turbors]

Do you look at injector d/c? I am very curious what normal is.

 

[jpolizo]

Originally posted by 92turbors
Do you look at injector d/c? I am very curious what normal is.

You're generally not supposed to go over 80% duty cycle -- although lots of folks seem to do it.

If you want to have some fun, here's a calculator to play with ...
http://www.rceng.com/technical.htm