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

 

[No_Skillz]

Do it again. Soapy water this time. I am betting on massive leaks at your TB and valve seals (at the very minimum). Post back with results: how much boost held for how long with no input into the system.

 

[domthebomb11208]

boost leak through the valve seals? how common is that?

 

[domthebomb11208]

how come i dont have problems when i'm a waste gate boost if it's a boost leak?

 

[No_Skillz]

There is a certain point where the ECU decides "ok, that's too much air, time to shut down the motor or we'll blow." This amount of air is detected by your MAF sensor. If you have boost leaks, your turbo will compensate to make up the boost, but there is also more air flowing in through the MAF (but leaks out and never reaches your engine, also affecting your tune). Wastegate boost is the lowest boost setting you can run, and this amount plus the extra due to your leaks might not cross that point set by the ECU. If when you turn up the boost and hit fuel cut, then it's more than reasonable to assume that you have a major leak somewhere.

The two places that I mentioned are very common places to leak. Do the test. You'll be stunned.

 

[Skunked tsi]

How much are you trying to boost? Also with an open dp are you creeping? Watch your boost gauge I would be willing to bet you are creeping, I am unsure how much boost you can run on a bone stock car but I am doubting its not much more then 16-17.
Tyler

 

[bartels903]

I ran 15 completely stock besides k/n boost gauge and controller, I'd put money on many boost leaks.

 

[tsimom]

Definitely do with soapy water and hopefully an air compressor.If you are trying to do with a hand pump it will be harder to hear or find. The soap will help you alot.

 

[JayRolla]

Yea I can run about 15-17psi before fuel cut on my 1g maf. Sometimes it cuts at 15 and sometimes it dont. Madders on how dense the air is on that day. Im also betting boost leaks. Stock fuel I would not run more than 14psi.

 

[domthebomb11208]

i got a 255 lph fuel pump in it. I got it to boost to almost 15 pounds today. If i do a 4th gear pull it doesnt fuel cut

 

[oldman]

I think you guys are giving the OP too much credit, I suspect a boost leak test was never done. "I didn't hear anything" indicates to me that OP was just revving the motor while listening for leaks. If I'm wrong, I would like to know from OP how much psi was registering on the boost gauge during the leak test.

 

[domthebomb11208]

it was holding a solid 12 pounds when i did the test

 

[1stGenRocks]

You need to test it at or above the boost pressure that your trying to run

 

[Soup Can]

Ok I'm completely stumped..stock 92 turbo...stock 14b, stock fuel, stock boost...still hitting cut at 12lbs...naturally assumed it was a boost leak, so did a check, no leaks..did the test 3 more times just to be sure @ 15psi held the pressure fine...any clue what else could be causing this? The only explanation I can think of is a boost leak, but myself and 3 other guys poored over the car with soapy water and couldnt find a single leak...on a weird wim though maybe it was rpm related so ran it to 6k at half throttle, no problem..stomp it at 2k and by 3500 when i hit 12lbs brick wall....also though it could be the maf, so swapped it out for another stock working maf, still get it...i ran the boost gauge from both the p connector and the fp actuator just to make sure i had a good source(suprisingly enough they actually both read dead even)...ecu is new so no cap leakage or anything...

SAFC isnt due in till next week so if all else fails I'm going to take a look at the karman counts and go from there...just thought maybe there was something stupid I was overlooking not boost leak related that I could check in the mean time...

 

[JayRolla]

Man I wouldnt know what to say then. I would do a boost leak test to 20psi and see what you come up with. Also with that safc I would get 550's and a 2gmaf and that should fix your problem. On the other hand if the 1g maf is cutting at 12psi maybe the 2g maf wont fix it.

 

[WeaselHack]

Do you have a data logger? If so, post some logs of a few pulls when this is happening.

Also, please fill out your profile sometime soon.

 

[Soup Can]

hmm i thought my profile was filled out...ill double check it again...logger is also inbound...

 

[WeaselHack]

logger is also inbound...

Awesome! The logger should shead some light on your issue. Until then your guess is as good as mine.

 

[syclone]

How do you know it is fuel cut?
what happens at 12 lbs, does it stumble or cut out? kinda shut off for a second?
or can you just not boost more than 12 lbs. as in a turbo or wastgate problem.

Jamie Sanders
1996 GSX (stuck as a newbe for 11 months now.)

 

[Soup Can]

3rd dsm...its fuel cut...brick wall....yea im just gonna recheck everything and wait for the safc so I can get an idea of the air counts...right now its like trying to hit a bullseye blindfolded

 

[gunner52]

im having the same porblem on a 95 gst the only things done to it are 2.5inch intercooler piping and the boost have been turned up to 15psi. it idles great and drives great till it hit about 4500-5000 rpm 1st gear dosent seem to have a problem but it starts cutting in 2nd and 3rd. i have a data logger at 4600 rpm my stft and lftf are at 0% and airflow is about 10.5 lbs at idle 850rpm stft 17% ltft 12% 0.45 airflow if you have any idea lemme know trying to get this think workin before i gotta go to work tonight if you need anymore info lemme know and i can take some more logs
ok just took it for another run and found that if i dont step on it just bring it up to 5-6k gently i dose fine but romp on it it starts cutting out

 

[joobienooner]

Okay so I had my boost set at 15 with my mbc on t-25 and I turned it down to what should be about 12 when i finished putting in my e316g because i havent had time to tune yet. But as im driving around I look at my boost just keeps climbing...all the way to about 17-18 and then i got fuel cut. So i pull over and turn the mbc down even more....Same problem. So i turn it as low as it goes and it still climbs to 17-18. Any ideas? My mbc is hooked to the jpipe and the actuator and no they are not hooked up backwards or anything. The turbo is basically brand new about 50 miles on it before i got it...no rust or anything and the actuator is MINT. I still have the stock o2 housing and its not ported either. iunno any ideas?


Thanks a lot,
Ryan

 

[delta448]

Ideas: Check the WG actuator, verify it is able to open the WG. Check for pinched or kinked vac/boost line on mbc. Make sure you adjusted the mbc in the right direction.

 

[Quasimondo]

Run a line directly from the compressor outlet to the wastegate. If your boost still rises uncontrollably, then you're probably suffering from boost creep. A search on these forums will tell you how to take care of that problem.

 

[Gst18]

Your problem sounds like Boost creep. What happens is your wastegate hole doesnt flow as much as its supposed too so when you start hitting boost it will keep rising until the wastegate is fully opened.

You can fix the problem by porting the turbine side of the turbo around the wastegate area. Porting it will allow more flow around that area to exit, thus eliminating boost creep. You can also upgrade the flapper to a larger sized one which should allow you to port the hole some more.
Boost Creep is too much air flowing past the turbine due to having too small of a wastegate hole.

Here is a link on how to port your turbo and eliminating boost creep.
http://www.dsmtuners.com/forums/showthread.php?t=186525

 

[oldman]

Boost Creep is too much air flowing past the turbine due to having too small of a wastegate hole.

Not exactly, the issue has more to do with flow characteristics. Enlarging the wastegate path is just a small part of boost creep porting, more importantly is to re-direct flow. Aside from this, good post.