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

 

[Defiant]

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

 

[Blktsi_awd_961]

Have you tried changing the sparkplugs recently. Mine would do that and it was just fouled plugs. Might as well get some ngk wires too. You also might want to try recircing you bov. Or, just a thought so don't hold me to it, it might be that the adjusting screw on the greddy bov is to loose. When you hit 17psi it might be coming open early which would cause you to run very rich. Next time it does it see if you can hear the bov releasing before you let off the gas. It took me a few days to finally get mine set right.

P.S. I would get the boost controller first, it sounds like you really need something to controll that spike!

goodluck!

 

[greenmachine97]

Ok thanks alot
i bought a new fuel pump, 190lph (caugt a good deal! 45shipped)
i am getting a Greddy MBC later this week, hopefully(anyone using this)
i am getting new NGK plugs and wires next week,(as long as i can get a job)
and then within the next few monthes i plan to get:
evo3 o2 housing (should i get ported)
evo3 manifold(ported or not?) my current one has a 3/4" crack
then pocketlogger and SAFC.
does this order of operation make sense? or is there a better plan? thanks alot for the help

-kyle
and anyone reading this in st. louis, who is good or decent at tuning, actually anyoen who has experience tuning. please pm me! thanks

 

[nine5raptor]

I wouldn't bother with the 02 housing or the mani. yet. Save the money for a bigger turbo and injectors.

 

[Talontid21]

I read in the power pages section of superstreet that I need an fuel cut defencer,I already added walbro 225lph fuel pump.Where can I get one,how does it work,how do I install?please help!Also,do you like my car?

 

[Attrayant]

Ok, here's the story.
1992 Eagle Talon, 6/4 Bolt TSI AWD.
STOCK except for there is no air canister, just a filter.
Engine has been rebuilt to stock roughly 3K ago.
Had a boost controller on it, but not anymore.
No aftermarket Boost Gauge
Stock gauge reads 14psi at WOT.
In 2nd gear it was floored and then bam, fuel cut. With no MBC on it anymore it should be back at stock boost, and the exhaust and intake are all stock witht he exception of the air canister being removed. Any ideas? I know fuel cut to be common on cars with upgraded exhaust or intake, but this one is pretty much 100% stock. TIA!

 

[allezgrand]

Fuel cut is also common on cars with an intake leak. Build or buy a boost leak tester and check for leaks.

 

[RipperXX]

Is this useing the factory BCS? or did you just run a line from the compressor outlet to the wastegate?

I dont think the stock pos boost guage should read to 14psi on stock boost. Get a pressure guage of some sort and see what its at. I know my white TSi never hit fuel cut except once when I forgot to hook up the line to the waste gate hello max boost

 

[Attrayant]

Found the problem. I hooked up my boost gauge using the FPR solenoid and went out for a drive. Just as the boost was about to hit 20psi I let off the gas and started tracing lines. Turns out the BCS vaccum line near the airbox was very loose and almost falling off. I secured it with some zip ties and now boost is a steady 13-14psi.

 

[jfdid]

90 6bolt with re-wired pump. My MBC was running pretty crappy, so I was boostin FULL ~21 PSI or so(I know, not good) Anyways, so I'd floor it and it would pull nicely until around 5500 or so, then it would stuble REALLY bad. Is this the infamous fuel cut from the ECU, or is it caused by not enough fuel getting to the cylinders? Any ideas? Would a 14B be able to produce enough air to cause fuel cut on stock IC piping? Thanks fellas/ladies.

 

[DSM_23]

yea that sounds like fuel cut to me, was there a loud backfire sound and all power was lost? Same thing happened to me the other day, just not with 21psi.

justin

 

[RiceKiller_TSi]

Originally posted by leet
I don't know why, but I REALLY wouldn't push your car to where it's hitting fuel cut all the time.

Yeah, but it hasnt hit fuel cut in over a year now. Before then it would hit fuel cut on cold nights. I didnt have the boost set really high and it was fine on the "usual" hot days here. But when the temp dropped the fuel cut kicked in. But like I said before, no more fuel cut...period, notta, nothing.

 

[Defiant]

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

"Should the ECU ever see an intake air mass greater than a certain preset level, it will stop fuel delivery and spark to the engine cylinders. This 'critical mass' depends on air volume, temperature and pressure, as measured by the MAS sensors. The act of the ECU cutting off fuel delivery to the engine is known as the infamous 'fuel cut'."

 

[bosljeff]

I have done the research, but I never found an answer regarding the effects of cold air.

Up until this winter, I have had my mbc up to 15 psi with no problems. As it has gotten colder, I will go to pass someone on the highway or launch hard to get across a 2 lane road and I swear to God it feels like my car is turning on and off, stuttering, and just basically suddenly driving like a piece of crap.

Can this be due to it being so cold that the air is more dense coming in thus adding air to the already higher boost levels and thus causing the ECU to cut fuel?

If so, I know once it warms up no prob, but should I start to consider a new fuel pump and/or rewire, new injectors, or what...and in what order of what to do first?

Thanks and sorry for the somewhat repetative question, hopefully it is unique enough I don't get destroyed.

Boz

 

[crankbender]

Fuel cut is not imposed by actual fuel rates but rather by the ECU based on air flow. The air flowing needs a certain ammount of fuel and the ECU cuts it when it decides it can't give that much fuel.

In general the only real way to get rid of fuel cut is to trick the ecu, replace it with a standalone, or reprogramm it.

Ways to do the first option
S-AFC
gm maf
2g maf
etc etc etc (just make sure you have the increased fuel flow capacity to match)

 

[bosljeff]

crankbender:
Not arguing, just learning:

All you said was great and all and will be done sooner or later, but for now, isn't it safe to say that I have "turned up my air" with my mbc etc and now I need to "turn up my fuel" by means of pump/rewire/injectors? Wouldn't that, in theory, allow the ECU to realize that ratio of fuel/air are correct thus eliminating the need to trick it?

It just seems that if you proportionately increase both air and fuel, you would never need to "trick" the ECU.

scrcco:
if a bigger turbo isn't for a long while, should I just keep the injectors I've got (stock), or can I upgrade them before a bigger turbo?

Discuss amongst yourselves.

Thanks,
Boz

Originally posted by crankbender
Fuel cut is not imposed by actual fuel rates but rather by the ECU based on air flow. The air flowing needs a certain ammount of fuel and the ECU cuts it when it decides it can't give that much fuel.

In general the only real way to get rid of fuel cut is to trick the ecu, replace it with a standalone, or reprogramm it.

Ways to do the first option
S-AFC
gm maf
2g maf
etc etc etc (just make sure you have the increased fuel flow capacity to match)

 

[crankbender]

All you said was great and all and will be done sooner or later, but for now, isn't it safe to say that I have "turned up my air" with my mbc etc and now I need to "turn up my fuel" by means of pump/rewire/injectors? Wouldn't that, in theory, allow the ECU to realize that ratio of fuel/air are correct thus eliminating the need to trick it?

The ECU can not measure fuel pressure and flow rates it only sees the air. It also does not look at the O2 sensor during WOT operation (open loop).

This means that even if you have 900-0000000 cc injectors and 50000000000 psi of fuel pressure if you put that much air past the mas it will impose fuel cut even tho you are drowning in fuel.

 

[candela]

In general the only real way to get rid of fuel cut is to trick the ecu, replace it with a standalone, or reprogramm it

Or get an HKS fuel cut defender

NOTE: I would have never posted this if I didn't see crank here. I am now an avid follower/smart-ass...

 

[Groomz]

www.dsmchips.com

Get the fuel cut elimination option ( along with whatever else he offers ) and you should be good to go. Only 90$ too.

 

[candela]

another option

 

[crankbender]

hey now getting rid of the fuel cut through reprogramming is the same as fooling the ecu.

Yeah before I went with DSMchips i would get the reprogrammer and burn my own chips....not that his arn't good but if you go the other route you can update to new injectors for like nothing.

 

[Groomz]

Originally posted by crankbender
hey now getting rid of the fuel cut through reprogramming is the same as fooling the ecu.

Fooling the ECU is done by altering the inputed values before they are received by the ECU. What the DSMchip does is remove the line coding for the "fuel cut". Not so much fooling as, well, reprogramming. The ECU is now not capable of fuel cut, as if it were never there to begin with.

 

[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....

 

[bosljeff]

Yeah, I may go with the dsmchips, I am not capable of making my own chips, so that will probably be my route.

So, when I get rid of fuel cut, what becomes the failsafe in place of the ECU's fuel cut? I don't want to end up causing what the ECU would have prevented, so what do I do to make sure I don't end up massively messing up my engine?

Is that where loggers and Fuel Management systems come in?

Hope that makes sense.

Boz

 

[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.