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

 

[steve]

It just means that something doesn't have the ability to deliver the proper amount of fuel anymore.

Please, we keep trying to kill that bit of misinformation. Fuel cut is caused by the metered air mass exceeding a trigger value in the ECU. When it does the ECU stops firing the injectors, cutting off the fuel. What the ECU is checking for is a runaway turbo from the wastegate or hoses failing.

The most common cause of fuel cut is a boost leak since that will cause your MAF HZ to be higher than it would normally be. Second most common cause is turning the boost up too far.

Assuming your hitting it because of the second reason, you can delay it by installing larger injectors and using an SAFC (or MAFT) to reduce the airflow a matching amount.
The only way to get rid of fuel cut is to modify the ECU. Any other decive the claims to fix fuel cut does so by limiting the airflow input to the ECU and can cause the engine to go lean once the device is active.

Steve

 

[DragSourceTsi]

I knew what I was trying to say and messed it up.

 

[exiletalon]

Mine was fixed with a new o2 sensor and buttoning up all the boost leaks

I know this sounds retarded, but how do I block off the MBC -to boost leak test it, I did it before- but I have never blocked off my MBC!

 

[Cool Mr Steve]

I'm not really sure where to start with this issue. My SAFCII is screwed up, and I have no idea what to do about it. At idle to about 2000 rpm (low throttle) I'm adding slight bits of fuel. After that I start taking out a small bit of fuel to keep my fuel trims happy. I have no idea what to do with my high throttle settings because when I get just above 3k and hit about 21psi my car cuts out, then bucks back up. Another guy on here responded to me and said that he does no adjustments on his SAFCII at idle, then by redline he is taking out around 17%. I wouldn't know how to take out fuel without being unsafe (as I can't really log very much because it cuts out so quick) but I can't figure out what else it may be. If I'm not taking out any fuel (actually adding fuel) with 550's, would I be more inclined to experience fuel cut? I found this on another thread about the subject

Fuel cut is caused by the ecu seening a large airflow value from the maf which works out to roughly 100% dudy cycle on stock injectors. If ya install 550cc injectors which are 18% bigger than stock injectors, then adj the afc to compensate for the larger injectors, you wont hit fuel cut untill you make up for tha 18% airflow buffer.
-andy

I'm not sure if this is correct, because I unfortunately don't FULLY understand fuel cut. If it is correct, though, it seems that would be the reason I am experiencing this issue. Any advice? BTW, by mid 3k RPM I'm only seeing (on my short logs) about 3 degrees of timing.

 

[Cool Mr Steve]

My logs look different all the time, but this is what they generally look like as far as the timing goes and the sudden drop in o2 voltage, although that happens at lower RPMs usually.

Time RPM Timing O2 1 Bank 1
00:02.3 2604 19 0.02
00:02.6 2428 29 0.76
00:02.9 2500 27 0.08
00:03.2 2552 22 0.82
00:03.5 2608 19 0.88
00:03.8 2680 16 0.9
00:04.0 2764 13 0.9
00:04.3 2840 10 0.92
00:04.6 2924 9 0.92
00:04.9 3044 8 0.94
00:05.2 3136 7 0.94
00:05.5 3276 3 0.94
00:05.8 3468 3 0.94
00:06.1 3592 4 0.94
00:06.4 3736 4 0.94
00:06.7 4260 5 0.04
00:07.0 4016 6 0.94
00:07.5 3692 33 0.54

 

[95blackGsTurbo]

Fuel cut is when you the stock MAF reads to much air flowing through it. Usually because of a boost leak. It does this because when you have a leak, not as much air gets into the throttle body so the turbo has to work harder and pull in more air to make the same amount of power and eventually the MAF reads to many Hz and you hit fuel cut. Doesn't actually have anything to do the running out of fuel or getting to much. I used to be confused by this too. You log looks really good once you reach full boost and until you let off.

 

[4g63tsiawd]

What are your settings at wot. You could be running way to rich and that is what is causing the fuel cut.

 

[Cool Mr Steve]

Well, those are the problems... #1, I don't want to let off, I am forced to because my car shuts down, and will continue to violently shut down/start back up if I keep into the gas. #2 my settings are 3% increase in fuel all the way to redline on 550's. PLEASE do not tell me that I should not be adding fuel. I know this. I'm not dumb. But I need to add some fuel at idle to have my short term fuel trims correct, and until I know that I'm getting too much/too little fuel under high throttle I don't want to go messing with my settings. After I get rid of this damned miss/shut down my car is doing, I can post an actual run and start tuning. For right now, I have no idea what is causing the miss.

 

[95blackGsTurbo]

You should be at around -10% at least from 3k-redline. Turn the boost back down to 15 or 16 again and start there with at least -10% fuel and if it reads decent slowly increase the boost. Can't get rid of the miss if you aren't going to adjust the SAFC. It's the only way you will figure out what's wrong. That and being 100% sure you don't have a boost leak. Always seems to be the problem on here.

 

[Cool Mr Steve]

Ok, lets say my SAFC just wasn't working correctly for some reason. If I took away 10% fuel and it made it run 10% too lean, I'm not sure if that could seriously hurt my car. I'm very new to the tuning game, and I'm timid about taking away that much fuel, since I actually have to add fuel at idle.

 

[97_eclipse_gst]

I finally got a chance to put my stock piping on and i think i fixed it. The car has not backfired yet and it feels like it running better. Thank you so much for all the help, and finally helping me solve my problem.

 

[Marc91GSX]

I am glad you got your problem fixed.

No offense but the answer to your problem was given to you on post #4 and again 10 posts later yet it still took you to post 22 to figure it out. Oldman is a wiseman for a reason and his advice is solid (most of the time ). Oh and here is a link for something that is a must have if you own boosted car.

http://www.dsmtuners.com/forums/showthread.php?t=201554

 

[dsm-onster]

Fuel cut is caused by the ecu seening a large airflow value from the maf which works out to roughly 100% dudy cycle on stock injectors. If ya install 550cc injectors which are 18% bigger than stock injectors, then adj the afc to compensate for the larger injectors, you wont hit fuel cut untill you make up for tha 18% airflow buffer.
-andy

This is 100% correct. All piggy backs becasue they cause your ecu to see less airflow thus lowering your injector duty cycles this makes it so that you can flow more air (turn the boost up) before having to pick you teeth out of your steering wheel from fuel cut.

At idle to about 2000 rpm (low throttle) I'm adding slight bits of fuel. After that I start taking out a small bit of fuel to keep my fuel trims happy.

You are tuning out your deadtime with your injectors. RC engineering injectors are known to have high dead times. What you are doing is the only way to tune it out with pigglyback. DSMLink would get you a much better tune, becasue you tell the ecu to include extra deadtime when calculating the duty cycle. But, nevertheless, you're doin gright and that makes sence that you have to do this.

you are getting significant knock at around 3Krpms. This may infact be "rich knock". "Rich knock" is a debated occurence where supposedly too much fuel leads to detonation.

The only way to know for sure if you're hitting fuel cut is to log a perameter that either shows Injector Duty Cycle directly or a perameter that can allow you to calculate duty cycle. If you have wideband just lying around, you cold see how rich you're running when you hit fuel cut. If it is in the single digits then you definately need to lean out. You have a decent fmic and you're running 21 psi on a ported big 16G. Could you just be flowing beyond the 18% buffer zone that the 550s lend you and consequently still getting fuel cut?

 

[jepherz]

If your injector duty cycles don't go to 0, it's not fuel cut. Fuel cut is commonly mis-diagnosed.

 

[97_eclipse_gst]

No offense taken but i did do a boost leak, a couple of them. The only the car would backfires would be when moving at WOT. I did the test in my driveway and it would never backfire there, only when moving. Thanks for the help everyone.

 

[Cool Mr Steve]

I wanted to log injector duty cycle as I know that would probably give me my answer. Correct me if I'm wrong, though, but I don't believe there is a function with my Pocketlogger setup to log that. I understand that fuel cut is caused by the ECU seeing too much air, so I was also curious if I could determine whether or not it was fuel cut by logging airflow? I know that there are many variables involved, but can I come up with (with my logging setup and injector size) a conclusion with the information I can log?

This is 100% correct. All piggy backs becasue they cause your ecu to see less airflow thus lowering your injector duty cycles this makes it so that you can flow more air (turn the boost up) before having to pick you teeth out of your steering wheel from fuel cut.

So from what he is saying (the original poster of what you replied to) since I am making basically no correction on my SAFC, I am not reducing the amount of air my ECU sees? Is that reason enough for me to assume fuel cut?

I see that I have knock, and I am hoping it is "rich knock." The car feels fairly sluggish when I stomp on it at lower RPM's in order to do a log, all the way until I start hitting high boost levels. Anything up to about 15psi or so it almost feels like I'm not gaining any more power. When I hit higher boost, though, it kicks in hard. How do you suggest I begin tuning? What would be a safe amount to take out, and where? I'm at about (high throttle) +2% across the board.

 

[MrNobody]

Do you have GM MAFT? or Stock? have you taken out then honeycombs(3 of the 4)? Have you adjusted the "lean/rich" screw on the bottom of your stock MAF if that is what you are using?

http://www.roadraceengineering.com/eclipsetech/2gmasadjustment.htm

This may help you. I dont know. Good Luck!

MrNobody

 

[dsm-onster]

I wanted to log injector duty cycle as I know that would probably give me my answer. Correct me if I'm wrong, though, but I don't believe there is a function with my Pocketlogger setup to log that. I understand that fuel cut is caused by the ECU seeing too much air, so I was also curious if I could determine whether or not it was fuel cut by logging airflow? I know that there are many variables involved, but can I come up with (with my logging setup and injector size) a conclusion with the information I can log?


So from what he is saying (the original poster of what you replied to) since I am making basically no correction on my SAFC, I am not reducing the amount of air my ECU sees? Is that reason enough for me to assume fuel cut?

You are running no correction at 21 psi?! You're hitting fuel cut. Peroid. That solves that mystery . You got higher than I did. I ate a few incisors the first time I ventured into 17psi teretory with an unhacked maf and stock fuel injectors. Your tuning as if you have stock fuel injectors if you have no base correction with your SAFC and are definately hitting fuel cut.

I see that I have knock, and I am hoping it is "rich knock." The car feels fairly sluggish when I stomp on it at lower RPM's in order to do a log, all the way until I start hitting high boost levels. Anything up to about 15psi or so it almost feels like I'm not gaining any more power. When I hit higher boost, though, it kicks in hard. How do you suggest I begin tuning? What would be a safe amount to take out, and where? I'm at about (high throttle) +2% across the board.

If you are running no correction for your injectors, then correct that first then do another log and see where you're at with knock retard. One step at a time. Everything may clear up . . .

 

[Cool Mr Steve]

Yep, I plan on doing just that. My main concern was that I'm not taking away fuel at idle, so I was scared to take it away at higher RPM's. You cleared that up though, so I'm going to start with taking away small amounts of fuel at a time. I pulled out -4% fuel on the way to my girlfriends house and made it to 4100rpm without fuel cut before I let off. I'll probably take out -10% and do a log and post it back up. It's fairly wet around here right now, so it may take a bit for me to actually log a run but I'll have it up asap. Thanks a lot, guys!

 

[Cool Mr Steve]

Time RPM Timing O2 1 Bank 1
00:03.9 2584 23 0.68
00:04.2 2664 22 0.82
00:04.5 2752 20 0.86
00:04.8 2856 16 0.86
00:05.2 2960 14 0.86
00:05.5 3108 10 0.88
00:05.8 3240 7 0.9
00:06.2 3436 3 0.9
00:06.5 3628 4 0.92
00:06.8 3796 5 0.9
00:07.1 4020 7 0.92
00:07.4 4208 8 0.92
00:07.8 4408 8 0.94
00:08.1 4592 9 0.94
00:08.4 4776 9 0.94
00:08.7 4940 9 0.96
00:09.1 5120 10 0.96
00:09.4 5296 10 0.96

-10% across the board. It's still wet out, so I was only able to pull until 5200. Does it still look like I'm too rich?

 

[ocdiddy02]

I have a 90 tsi awd. I got a big 16g, turboback exhaust, 560cc injectors, walbro 190 fuel pump and when i race or floor it i get a fuel cut off in like every gear at about 5500-6000 rpms...this causes me to shift at like 5500 and i am losing so much speed....any suggestions on how to fix the problem or what is causing it?

 

[Maverick3169]

What are you using to tune your car?
Also, what kind of boost pressure are you running?
Do you have a datalogger or a wideband?

 

[iceman21221]

My car was doing the same thing. I did a boost leak test and the black injector seals that are in the head were old and leaking air very bad. My car was only hitting fuel cut in 4th gear at full throttle in the same rpm range. After a while it got worse and was doing it in 3rd 4th and 5th. Since i replaced all the injector seals i havent had any problems yet. Try doing a boost leak test and see what turns up.

 

[Hurleyatticus4]

Do you have an Air/Fuel gauge? Are you running rich? Do you have an AFC? What kind of intake do you have? You need to put all these things into effect and figure out if it is something as simple as your air/fuel mixture and combustion.

-Alex

 

[Chaddycakes21]

Perform a boost leak test.