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

 

[project_tsi]

boost leak test...

I didnt think of that. Ill do that. Thanks

 

[LiquidOC]

OK, this has been happening for over a while now, however, it doesn't affect normal drivability, other than really crappy gas mileage.

About last July, my timing belt slipped, and i bent every single exhaust valve, took it to a shop (had it towed) and got an all new timing belt, brand new valves, springs, and rocker arms (version 3, i believe) plus a mild port and polish. This guy refused to take out my balance shafts, so I just kinda said to make sure it was done right. Apparently, it wasn't (now I find this out.) so my balance shafts are out of phase, So I know that that is at least part of my problem, more than likely. Also, when I went to pick up my car, it was hitting fuel cut at around 4000 RPM's. ECU was replaced with a 97 GSX one, and spark plug wires re-routed so they didn't fire improperly. Also, I was informed that my Manifold Differential Pressure Sensor was bad, and that I should replace that, plus my rear O2 sensor was bad, and I should get that fixed as well.

Got the rear o2 replaced, and the manifold differential pressure sensor, still haven't fixed the out-of-phase balance shafts, but I am working on scraping together the cash for that. Basically, what is happening is that I have a check engine light that pulled up two codes before I replaced the Manifold Differential Pressure Sensor. It would come up with a "Secondary Emissions system failure" and a P0170 "Fuel Trim Malfunction: Bank One" Recently, after i put the new MDP sensor in, the check engine light went away for about 50 or so miles (because I reset the ecu) when it came back on, it was only throwing the P0170 code, and still hitting fuel cut. What all can possibly make it do this, from a mechanical aspect....is it possible that the ecu is bad, and I should try another one? Maybe my Front o2 sensor is bad, and I need a new one? I know I'm running rich as hell, because my carbon build-up is horrible on my muffler and slightly on my rear bumper. Also, when I floored it after I installed the new sensor (after I let it warm up) it didn't hit fuel cut right away, and it pulled like a raped ape. Big puff of smoke came out of the tail-pipe when i hit around 4,000 RPM's in second, and then in third, it hit fuel cut. I reset the ECU once more, and have returned to driving it like a grandma, only flooring it when I absolutely have to. Is it possible that everything is fine, and my balance shafts are causing the ECU to pull back because it thinks that the engine is knocking? Or could it be a dirty injector or something?

Any help is appreciated, thanks for reading the long-ass post.

EDIT: Also, it hesitates when I do punch it from any point in the RPM band in second, third, and fourth, no hesitation in first or fifth.

 

[jay_rod24]

OK, this has been happening for over a while now, however, it doesn't affect normal drivability, other than really crappy gas mileage.

About last July, my timing belt slipped, and i bent every single exhaust valve, took it to a shop (had it towed) and got an all new timing belt, brand new valves, springs, and rocker arms (version 3, i believe) plus a mild port and polish. This guy refused to take out my balance shafts, so I just kinda said to make sure it was done right. Apparently, it wasn't (now I find this out.) so my balance shafts are out of phase, So I know that that is at least part of my problem, more than likely. Also, when I went to pick up my car, it was hitting fuel cut at around 4000 RPM's. ECU was replaced with a 97 GSX one, and spark plug wires re-routed so they didn't fire improperly. Also, I was informed that my Manifold Differential Pressure Sensor was bad, and that I should replace that, plus my rear O2 sensor was bad, and I should get that fixed as well.

Got the rear o2 replaced, and the manifold differential pressure sensor, still haven't fixed the out-of-phase balance shafts, but I am working on scraping together the cash for that. Basically, what is happening is that I have a check engine light that pulled up two codes before I replaced the Manifold Differential Pressure Sensor. It would come up with a "Secondary Emissions system failure" and a P0170 "Fuel Trim Malfunction: Bank One" Recently, after i put the new MDP sensor in, the check engine light went away for about 50 or so miles (because I reset the ecu) when it came back on, it was only throwing the P0170 code, and still hitting fuel cut. What all can possibly make it do this, from a mechanical aspect....is it possible that the ecu is bad, and I should try another one? Maybe my Front o2 sensor is bad, and I need a new one? I know I'm running rich as hell, because my carbon build-up is horrible on my muffler and slightly on my rear bumper. Also, when I floored it after I installed the new sensor (after I let it warm up) it didn't hit fuel cut right away, and it pulled like a raped ape. Big puff of smoke came out of the tail-pipe when i hit around 4,000 RPM's in second, and then in third, it hit fuel cut. I reset the ECU once more, and have returned to driving it like a grandma, only flooring it when I absolutely have to. Is it possible that everything is fine, and my balance shafts are causing the ECU to pull back because it thinks that the engine is knocking? Or could it be a dirty injector or something?

Any help is appreciated, thanks for reading the long-ass post.

EDIT: Also, it hesitates when I do punch it from any point in the RPM band in second, third, and fourth, no hesitation in first or fifth.

Well, I'm not a wiseman...heck I'm not even a man. But I'll chip in my nickel.

ECU sees too much air = fuel cut. Have you checked for boost leaks? How do you know your balance shafts are out and how have you stood to drive it that way for so long? (since July)

 

[LiquidOC]

Not sure that it's fuel cut, but i am certain that My balance shafts are out of phase. I am actually in the process of aquiring a beater car so i can get this car fixed. Anyways, I am fairly sure that there are no boost leaks, but I will check when I get home tonight (hopefully, i can check without making anything that costs me money) I might even take it down to the local ricer shop here and see if they have a boost leak tester. Hopefully, they can't screw that up.

 

[punishercb]

Out of nowhere my car is starting to act up. I'm hitting fuel cut in 2nd at around 5k. I don't know why because all I have done is a MBC, 3" exhaust, and intake. I'm still at 13 psi because that's all my stock BOV can handle. Does anybody have any idea why this is happening?

Also, my speedometer is going haywire! Whenever I accelerate or boost, my speedo will jump back and forth? What the heck?

 

[oldman]

Boost leak is one of the main causes of an early fuel cut.

 

[punishercb]

You know, I was thinking the same thing. I'm thinking that it has to be the leaky BOV. I have the MBC as low as it can go, and it reads 13 psi, but I think that's because the extra pressure is just leaking through. Could that be a significant enough leak to have this fuel cut? Thanks.

 

[oldman]

You're welcome, the only way to find out is through a boost leak test so get going with it.

 

[punishercb]

Yeah, that will be my weekend project. So does anybody have an idea why my speedo is acting wacky?

 

[DARTHGST]

MY 98 GST HAS A UPGRADED FUEL PUMP EVO 3 16 G TURBO 550CC INJECTORS AND A SFAC I AM NOT A MECHANIC BUT THE LOCAL DSM TUNING SHOP HAS BEEN TUNING THE CAR HE CUT THE HONEY COMP MAF UP SO NOW I CAN RUN 17-18 PSI BUT NO MORE CAUSE IT WILL CUT THE SHOP SAYS I SHOULD GET A GMAF AND THAT WILL GET RID OF FUEL CUT I WOULD LIKE TO RUN 21 PSI EVENTUALLY. OR SHOULD I GO WITH A DSM LINK. MY NEXT MOD IS A 3" TURBO BACK EXHAUST BUT AFTER THAT THIS FUEL CUT IS A PRESSING ISSUE I HAVE THE EXHAUST JUST WAITING TO INSTALL IT SO ANY HELP IS APPRECIATED I ALSO DON'T WANT TO UPGRADE TWICE

 

[Cool Mr Steve]

Alright, I am about to install a Big 16g on my car... If you don't feel like looking in my mods list, my fuel supporting mods include a Walboro 255lph fuel pump and an AFPR. My datalogger will be here shortly. Anywho, I wanted to know at what boost level (on the Big 16g) my stock 450's will be at 100% duty cycle. Is it dependent on anything? I'm not sure if I'm asking the correct questions, but what I'm trying to understand is at what point I might be hitting fuel cut. Am I just completely missing the concept of fuel cut? Man, I suck...

 

[dave99gst]

whats to miss ? when you flow more air then your mass can handle your ecu will CUT the fuel. do you have a fmic ? upgraded i/c pipes ? exaust ? s-afc? all this will play a factor as to how much boost you can run w/o hitting fuel cut. as a ballpark guess. you can prob do 10-13 psi no prob.

 

[Cool Mr Steve]

whats to miss ? when you flow more air then your mass can handle your ecu will CUT the fuel. do you have a fmic ? upgraded i/c pipes ? exaust ? s-afc? all this will play a factor as to how much boost you can run w/o hitting fuel cut. as a ballpark guess. you can prob do 10-13 psi no prob.

Too busy to look at my vehicle profile? Alright... I have a JohnnyRaceCar FMIC w/ custom hard piping, stock downpipe & cat to 2.5" catback exhaust, and no S-AFC. So what exactly needs upgrading on my system to allow for me to boost at happier levels (18-19 psi)? S-AFC + injectors are already on the waiting list, anything else? 550's will work for 19psi, correct?

 

[unior]

MY 98 GST HAS A UPGRADED FUEL PUMP EVO 3 16 G TURBO 550CC INJECTORS AND A SFAC I AM NOT A MECHANIC BUT THE LOCAL DSM TUNING SHOP HAS BEEN TUNING THE CAR HE CUT THE HONEY COMP MAF UP SO NOW I CAN RUN 17-18 PSI BUT NO MORE CAUSE IT WILL CUT THE SHOP SAYS I SHOULD GET A GMAF AND THAT WILL GET RID OF FUEL CUT I WOULD LIKE TO RUN 21 PSI EVENTUALLY. OR SHOULD I GO WITH A DSM LINK. MY NEXT MOD IS A 3" TURBO BACK EXHAUST BUT AFTER THAT THIS FUEL CUT IS A PRESSING ISSUE I HAVE THE EXHAUST JUST WAITING TO INSTALL IT SO ANY HELP IS APPRECIATED I ALSO DON'T WANT TO UPGRADE TWICE

well first off you should never hack a 2g maf - they suck hacked

second off you shouldn't be getting fuel cut on properly tuned afc/550 combo @ 18 psi

and it sounds like stockish exhaust even?!

 

[Jon_0_3]

i will be driving down he street and my car just feels slow then when i put my foot down farther the car will take off and the trany will jerk. how can i solve my fuel cut. also my car is running rich whats goin on with it?

 

[ChrisFlo]

Its often times a boost related issue. What boost are you running and on what setup?

 

[GSTROJO]

You can always get bigger injectors(if your still on the stock 450s) get some 550's, and a 190lph or 255lph fuel pump.

 

[Jon_0_3]

every thing on my car is stock. if i get 550s and a fuel pump this can solve it?

 

[mitdrx]

You should use the hks fuel cut defencer version 7 which is dsm specific. It will override the fuel cut and you dont have to remove any honeycomb which would give you a rough idle anyways. Not to mention its just over a hundred bucks.

 

[CanadianTSi]

Just fix your boost leak and you will be fine.

 

[CanadianTSi]

550's will work but 650's would be better, so that you don't need to upgrade twice.

 

[steve]

Just fix your boost leak and you will be fine.

Exactly!

Steve

 

[oldman]

i will be driving down he street and my car just feels slow then when i put my foot down farther the car will take off and the trany will jerk. how can i solve my fuel cut. also my car is running rich whats goin on with it?

This doesn't sound like fuel cut, you need to provide more info than just "trany will jerk".

You can always get bigger injectors(if your still on the stock 450s) get some 550's, and a 190lph or 255lph fuel pump.

fuel cut has little to do with the size of your injector or fuel pump, it has to do with the air count off the maf.

every thing on my car is stock. if i get 550s and a fuel pump this can solve it?

NO!

You should use the hks fuel cut defencer version 7 which is dsm specific. It will override the fuel cut and you dont have to remove any honeycomb which would give you a rough idle anyways. Not to mention its just over a hundred bucks.

Not true, a fuel cut defender will only delay fuel cut. The only way to remove fuel cut is to re-program the ecu.

Just fix your boost leak and you will be fine.

Agreed.

 

[oldman]

Am I just completely missing the concept of fuel cut? Man, I suck...

Yes you are. You're worrying abut fuel starvation, not fuel cut. Like Dave have already mentioned above, fuel cut means the ecu stops the firing of fuel injector when it receives signals from maf that exceeds the preset limit programed into the ecu. Fuel cut has little to do with your fuel system, in fact it's impossible for you to hit PROPER fuel cut on a stock fuel system even with upgraded IC and pipes because it simply can not supply enough fuel for you to hit PROPER fuel cut, you will hit fuel starvation first. So why do people hit fuel cut? Most of the time, the cause is either boost leaks or malfunctioning maf causing inaccurate signals being sent to the ECU.

 

[Jon_0_3]

ok i can feel the trany jerk. if it is boost leak how do i fix that