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

 

[bosljeff]

Kick ass advice! Thank you.

I do think it is fuel cut because this one time (at band camp), I went to cross two lanes of traffic, saw an opening, "launched" and the brick wall comparison seems accurate, however, I will still check plugs and wires, do the fuel pump rewire.

I have the NGK bpr 6 or 7 ES, whatever one is for more modded vehicles, and I need new wires though.

As for the test:

"To see if you might be running lean, pull a sparkplug and examine it for deposits. If it's white and has little bubbles on it, thats from your aluminum pistons or parts of your valve/cylinder head melting and sticking to the electrode."

If it is white and bubbles=running lean i.e. too much air?
If it is *blank*=running rich i.e. too much fuel? What are these 'symptoms'? Fill in the "*blank*".

Where can I start to diagnose fuel delivery, air metering, and/or ignition problems? Signs/symptoms?


Thank you very much guys. This has been a great help and will give me something to do over spring break.

Originally posted by psychlow
If your car is jerking/studdering, you do not have fuel cut, you have a fuel delivery, air metering, or ignition problem. Fuel cut feels like you hit a brick wall.

If indeed you do have fuel cut:

Major causes of fuel cut are low temps and boost leaks. Boost leaks cause fuel cut because turbo's swallowing in a large amount of air that gets read by the MAF, but it's venting it to atmosphere via a boost leak before it hits the engine.

As crankbender stated, DSMChips and other EPROM chip replacements don't remove fuel cut, they just change the code to such a high value that you'll never come close to hitting it.

If you get 660 CC injectors, a 2G MAS and an AFC, you're doing the same thing, just to a lesser extent.

If you do NOT have fuel cut:

- Check your spark plugs and wires! Turbo DSMs eat these things like candy. Make sure your plugs are gapped correctly and test your plug wires for proper resistance, ESPECIALLY if they are stock or old.
- Rewire your fuel pump. You may not be getting enough fuel flow and you might be running lean with the denser, cooler air.
- I noticed you removed the honeycombs from your MAF. This may be contributing to the above.

EDIT:

To see if you might be running lean, pull a sparkplug and examine it for deposits. If it's white and has little bubbles on it, thats from your aluminum pistons or parts of your valve/cylinder head melting and sticking to the electrode.

If you remove/delay fuel cut, from there your failsafes are going to be a good EGT and a logger. If you have bucks, invest in a wideband O2 with an in-cockpit LED display.

 

[Groomz]

Originally posted by crankbender
that was directed at candela sorry.

If you look at the ECU as the computer not the memory you are basically fooling it by changing the code on it without it knowing....

No problem.

Were not talking about some self concious AI construct here ( too much Sci-Fi, I know ).

Quoted from DSMchips.com

"This limit can be raise, like by a certain percentage, or totally eliminated."

You can have him raise it if you are uneasy about it not being there at all. The ECU is just using the coding it has stored in it to perform its functions. Remove that coding and the ECU "thinks" that it was never there to begin with. I am not a computer genius though, so if some other, wiser, computer geek could drop in, that would be nice.

Safe boosting,

 

[psychlow]

If it is *blank*=running rich i.e. too much fuel? What are these 'symptoms'? Fill in the "*blank*".

If you're running rich and you've just gone for a run around the block and come back, your plugs should be wet with fuel. If you've been running rich for quite some time, your plugs will be black/sooty with carbon deposits. Another way to check for a rich condition is to have a buddy drive (or vice versa) at WOT while you/he looks at the exhaust. If you get puffs of black smoke from the tailpipe, you're probably running rich.

Here's an article on reading sparkplugs.

"This limit can be raise, like by a certain percentage, or totally eliminated."

I'm not sure how good the guy is who does DSMChips, but most people (including TMO, when they were in the business of making ROMs) only raise(d) the limit to a such rediculous value that it would never be reached.

Maybe DSMChips has found a way to de-ASM the hexadecimal code, though. If you look at the data you download from a ROM chip, it's almost just an endless string of numbers.

Stock chips have a routine when the airflow is compared to a set value, with is A0 (106 decimal). By changing this value to FF (255 decimal), you can make fuel cut high enough that it will not be reached.

The string surrounding fuel cut is as follows:

25 02 D6 57 C1 _ _ 24 05 C6 28 F7

A stock chip will have A0, a TMO chip will have FF, and some other cars have different values.

AFAIK, if you outright elminiate this code, you'll cause massive errors. I wonder if DSMChips may be inputting "00", which may cause the ECU to ignore fuel cut altogether.

 

[RiceKiller_TSi]

Originally posted by Groomz
The ECU is now not capable of fuel cut, as if it were never there to begin with.

My ECU decided to do this on its own thus eliminating the need for me to buy fuel cut defenser options. It just got tired of cutting the fuel one day and now it pulls strong no matter what boost level I'm running. Good thing I have a logger.

 

[Eppigy]

I keep getting massive fuel cut at exactly 4000 rpm. WTF? I would be extremely greatfull if some could help. THANKS!

 

[91awd]

I use to get fuel cut all the time untill I got a 2g mass now I have no problems. You can buy them pretty cheap now with the plug and they are very easy to install.

 

[kpt4321]

A 2g MAS will not do you any good unless you get a set of larger injectors to go with it.

Check the car for boost leaks. Any boost leak will make you a lot more likely to hit fuel cut.

A pressure tester is a turbo car's best friend.

 

[Joe97Gsx]

What's the maximum air flow in lbs/min that a second gen mas can handle before it hits fuel cut?
So far the highest i've seen on my car was 34.02 @15psi @ 6400rmps.....
I tried to do a third gear pull @16psi but i hit fuel cut at about 6000rpms... but never got a chance to see where it maxed out.....
This is on a T04 60-1......

Thanks for you input....

 

[bosljeff]

Did the fuel pump rewire, might be a 'placebo' effect, but it seems to run smoother. I may up the boost back to 15 again, not sure.

I also included a toggle on the ground wire of the rewire setup. That allowed me to have added anti-theft benefits. With the hidden switch, I can turn off my fuel pump and the car can't be driven. I was just excited about it and had to share.

I'm thinking of cleaning the injectors, new fuel filter, and new wires.....that should help with fuel delivery, right?

Thanks again all, take care.

Boz

 

[92awddsm]

Originally posted by kpt4321
A 2g MAS will not do you any good unless you get a set of larger injectors to go with it.

Check the car for boost leaks. Any boost leak will make you a lot more likely to hit fuel cut.

A pressure tester is a turbo car's best friend.

Why do you need injectors with a 2g mas? Ive seen them work fine with stock injectors. A mustang on the other hand needs injectors with an upgraded mas. Seems like you are getting Mustangs and DSM's mixed up.

 

[starr]

my car without a boost controller and stock except for a bov had around 14 to 15 pounds of boost. i put on the dejon uicp blow thru with the ls1 3" maf and the maft just plugged in the dip switches in the right positions, and all the knobs set to zero and without the rpm wire tapped, and i also put on a manual boost controller, and now when i take the boost controller out to run 15 pounds of boost, in 2nd gear at wot i get fuel cut. i've never had fuel cut before and my boost gauge said i had 15psi when i didn't have the blow thru or the boost controller. thanks.

 

[Tallen]

You are still close to stock, but not quite. Try tuning the car a little. The MAFT zero'd is not always the orrect settings that you need. All cars are different, especially after modding. You can tune by o2 voltage, may want to look into an O2 voltage meter (do not get an autometer blinkey light POS gauge)

 

[starr]

but am i incorrect in saying that with the rpm wire NOT tapped, that adjusting the maft won't do anything?

 

[Tallen]

Ah I missed that part....tap your RPM and get to tuning. Double check the dips as well. If your getting fuel cut like symptoms, check for bbost leaks. Thats another likely source

 

[2Quick4You]

I just installed my turbo back 2.5 inch exhaust and a high flow intak pipe+K&N filter , Now i hit fuel cut even if my boost is turned down to 11 Psi ..... Im not getting any boost spikes or anything ..... It cuts fuel at about 5000 rpm .......What should i do to stop the car from hitting fuel cut .....

 

[girlieracr4g63]

Do you have any fuel mods done? ie fuel pump , afc, anything?

 

[2Quick4You]

Originally posted by girlieracr4g63
Do you have any fuel mods done? ie fuel pump , afc, anything?

No i dont , all i have is intake , exhaust ,thats it .....

 

[Insearchofatsi]

Fuel cut around the 5k rpm range seems to be a problem for dying ECUs. Two of my buddies had this problem, they just replaced ECUS... hope this helps. A

 

[Loco Diablo]

I know the techs on this site had gone over a million times bout the fuel cut, but i really couldnt find what i was looking for so im gonna ask if they can help me or anybody else can with this fuel cut thing.

car : Eagle Talon 91
Turbo : EVO III
550 Injectors
My ECU does not have a chip i guess its an older model, how can i work around this problem with what i got ?

 

[Eclipsed]

Originally posted by Loco Diablo
I know the techs on this site had gone over a million times bout the fuel cut, but i really couldnt find what i was looking for so im gonna ask if they can help me or anybody else can with this fuel cut thing.

car : Eagle Talon 91
Turbo : EVO III
550 Injectors
My ECU does not have a chip i guess its an older model, how can i work around this problem with what i got ?

Am I correct in reading you have 550s in the car with no sort of tuning device? And EVOIII is that a 16g?

Seems as if it could be fuel cut being that you have NOTHING to tune with. Get something to tune with ASAP like an SAFC or DSMlink.

 

[talontsi01]

I would like to know if there is a way to differentiate fuel cut from maxing out your injectors.

 

[unlikely hero]

No datalogger but I'm planning on one in the near future. I'm runing 92 octane(best I can find up here in ND) and I'm set at 1bar. With the b16g though I do creep up to 1.5 sometimes. Its just werid that it only does this between 3-4k. If I keep the revs up between shifts and hit second at 4k theres no problems. Its only when I shift it into like 3.5k. I don't know if its fuel cut but it feels like it. I have no power I mean I'll pump the gas and nothing even w/ the clutch pushed in. Once I coast down under 3k then it runs fine. Never have had this before.
=Jason-

 

[Loco Diablo]

Thank you anyways, installed MAF now im able to boost it all the way 25, and yes evo III is a big 16 g

 

[Boost Deez]

you can always upgrade to 550's that could be the reason because your running alot more air now you gotta make up for it with bigger injectors

 

[Pureplaya]

Alright guys I know this has probably been answered in some way but I'm looking for a straight answer. I'm runnin around 16psi boost and i'm getting fuel cut whats the best thing to get to stop this. On buschur racing they say something about the Vein Pressure Converter should I get that