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

 

[eclipsegsx1736]

As a side note, I hope you have a fuel pressure regulator on your 255 pump. Fuel cut can be caused by a boost leak, by adding too much fuel on an SAFC, or by boosting too high. You said you found "a couple little leaks." These can add up to quite a lot, try to fix them all before looking elsewhere.

 

[oldman]

As a side note, I hope you have a fuel pressure regulator on your 255 pump. Fuel cut can be caused by a boost leak, by adding too much fuel on an SAFC, or by boosting too high. You said you found "a couple little leaks." These can add up to quite a lot, try to fix them all before looking elsewhere.

Well said. Just to add, boosting at 21psi requires pressure testing of the intake up to 25psi.

 

[Ultimatedsm]

Just curious, what is your SAFC set to? And are you logging your car?

 

[xcelr8n]

Fix the boost leaks first, than try logging it, and leaning the car out... that should fix it.
If not than lower the boost but first two steps should fix it, possibly just the first step though.

 

[97_eclipse_gst]

Yea at first i had a exhaust leak and thought that was the reason the car is backfiring but it wasnt. And there has been a full boost leak check done to the car multiple of times and there is new wires and plugs in the car.

Also the first time the car ever backfired was right after i put my intake pipe on so im going to try to put the stock piping back on and see how it go's from there.

 

[Maverick3169]

I put some RTV on the J-pipe, because for some reason it seems to like to leak on my with just a gasket.

Now I just drove it after the RTV cured, and its doing the same thing.
Part throttle (like 80%) I can rev as high as I want and it stays in the high 10's for A/F. Once I go WOT, it reads lean and hits fuel cut. This is really getting on my nerves. I really don't know what else to do right now... this is really wierd. Why would it only lean out at WOT? I even went on the highway and took 20% fuel OUT at those rpms, and nothing changes. This makes zero sense...

Someone please help, I'm running out of idea's.

 

[Staytuned]

How old is your fuel pump? and what kind of fuel pressure are you seeing above 5500 rpms?

 

[Maverick3169]

Its about a year and a half old. I'm still using the stock FPR.

You have to keep in mind that all of this started immediatly after the new turbo install.

 

[Staytuned]

I am guessing lack of fuel up top due to a coincidental malfunction, a pre-O2 exhaust leak causing a fake lean condition or a bad O2 sensor.

 

[Maverick3169]

Now, how big of an exhaust leak would it have to be? I can find once before the O2 housing by just listening for it. I know that the gasket between the turbo and manifold was super thick (extreme psi gasket), would that cause this?

Also, is that a good way to check the O2 sensor? I've only had this wideband for a few months.

Doesn't this strike as being a bit odd? I can make the car rev all the way to redline at like 80-90% throttle, but once it goes WOT, this problem occures.

 

[Maverick3169]

Also, I just installed a brand new Evo III exhaust manifold, so the manifold itself is not leaking. The only exhaust leak that I can hear is comming from the downpipe/O2 housing gasket. Its a small leak though.

Thanks for helping me out.

 

[96eclipsex]

Okay I have a turbo 420a motor with a S-AFC 2, the S-AFC2 is set at o% across the rpm range, but i also have a 12:1 fpr and the cars fuel air mix is just about perfect. When I hit about 8 or 9 psi i have fuel cut.
I was wondering if anyone knows how i adjust the s-afc2 to eliminate the fuel cut or will I have to buy a fcd???

 

[95blackGsTurbo]

Are you sure you don't have any boost leaks? Those are the main cause of fuel cut.

 

[FastGS-T]

fuel cut is an air overflow to the ecu.... Check for boost leaks. and are you trusting a 12:1 a/f ratio to a fpr to handle? Get a wideband and logger or something to tune with and maybe that will help

 

[96eclipsex]

im not sure but if i had a boost leak would i be able to do 8 or 9 psi with no problem

 

[95blackGsTurbo]

Depending on your injector and turbo size you should be able to. What turbo and what size injectors you running.

 

[96eclipsex]

t3/t4 hybrid xs power turbo and stock injectors

 

[96eclipsex]

and would a little leak hurt anything

 

[FastGS-T]

a leak will cause fuel cut, just make sure all of your couplers are on snug, tight, and even... search on doing a boost leak test.

 

[exiletalon]

I purchased a 95'TSI AWD about 8 months or so ago, there was an issue that prevented me from revving past 4-4500 RPM, I didnt know what is was? The engine blew so I replaced it with a newer 97' 7 BOLT, The fuel problem is still there! What I dont understand is why I would be hitting fuel cut ( I have a S16G, 3" exhaust- but stock fuel-10PSI) I replaced the entire engine including injectors, manifolds. But the turbo and fuel pump are the same!
My true question is that after all of that, I have come to the conclusion that it is either the wastegate, or the stock fuel pump!- Any information would be helpful, and as to a solution, links or in-depth explanation would be helpful ( I'm confounded! )


OLDMAN- I have already boostleak tested it, as it is the first thing I always do when there is a problem that arises!- I have learned well!

 

[exiletalon]

I am running 91 octane. and only 10 psi until I get my 190 rewired and installed!

 

[Scott_S]

Have you checked the O2 sensor?

 

[4g63tsiawd]

Have you replaced your O2 sensor.

 

[DSMcamaro]

No need for the repost.
http://www.dsmtuners.com/forums/showthread.php?t=217818

 

[exiletalon]

Sorry, I did not mean to put it in here. So I reposted it in the problem diagnostics. Sorry about that one - my mistake, no excuses.
No, I have not changed the O2 sensor, as it was changed 2000 miles ago, and I checked it. It looked in great shape!- I dont want to spend $200 and have it not fix my issue. Could there be any other item that could cause this sort of problem.
Thank you!