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

 

[oldman]

For some reason I completely missed the maft part in your second post. Boost leaks before the sensor will not cause fuel cut, though it will effect the efficiency of the turbo and intake temperature. With that said, who is to say you have no leaks after the maft, perhaps you were on the verge of hitting fuel cut with your setup and the cooler temperature via the fmic put you over the top. In any case, the leak test should be done, at least it will allow you to move on to something else.

 

[dsm_illicious]

I installed new IC piping about three weeks ago and my car was hitting fuel cut like no tomorrow. It was, obviously, a leak. How could installing a more efficient intercooler mess with your air/fuel settings to that extreme? I don't see it. You most likely have a leak as well, especially since you mention the fact that you've just installed a new FMIC, and there is a good chance that something is loose or connected improperly.

 

[steve]

For some reason I completely missed the maft part in your second post.

As did I.

Were you running the MAFT in blow thru with the SMIC too?

Like Bruce said, you could have been just under the trigger before and upping the boost put you over but there are still plenty of things that can leak from the throttle elbow back. For example, with the stock setup anything leaking past the PCV stayed in the system because the breather was routed to the intake pipe.

16 psi on an EV0 III with stock 450cc injectors is likely asking a bit too much from them. I was going over 100% DC at 14psi with my B16G.

Steve

 

[shallowshowcase]

well the two hoses connecting to my intake pipe are just hanging, i didnt hook them back up, is that a prob...

i guess i had my 15psi tune maxed out and upping it to 16 was the straw that broke the camels back, i turned it back down and am re-evaluating my tune with the fmic, and looking for boost leaks, thanks agian

 

[oldman]

well the two hoses connecting to my intake pipe are just hanging, i didnt hook them back up, is that a prob...

Can you elaborate? I'm hoping you didn't just leave two open holes on the intake pipe.

i guess i had my 15psi tune maxed out and upping it to 16 was the straw that broke the camels back,

Also don't forget cooler temperature alone at the same psi will increase air density and therefore air mass.

 

[shallowshowcase]

ok now this has become more of a tuning situation i guess.... im wanting to go as lean as possible at WOT with as good of a timing advance as i can get without knocking (any pull in timing at all = bad) right?

i know o2 voltages are more of a guide and i shouldnt rely on them so i watch timing advance and tune for that...


so i was probably not leaning it out enough w/ the SMIC and moving to a FMIC pushed it over the edge right?

 

[oldman]

so i was probably not leaning it out enough w/ the SMIC and moving to a FMIC pushed it over the edge right?

I will let steve speak for himself. What I meant by this statement

With that said, who is to say you have no leaks after the maft, perhaps you were on the verge of hitting fuel cut with your setup and the cooler temperature via the fmic put you over the top.

is this: The stock fuel system simply will not support enough air flow for you to hit fuel cut, you would hit fuel starvation before you come anywhere close to hitting fuel cut. I do not think this is a tuning issue at all, In fact, I think any adjustments you need to make on the maft is an indication that there are problems. With a properly calibrated maft and stock injector, no adjustments should be needed. This what I think might be the cause.

1. You're not hitting fuel cut.

2. You have leaks after the maft with your old setup which cause you to almost hitting fuel cut and the cooler temp and extra psi put you over the top. This is what I meant by the above statement.

3. Defective maf/maft sending wrong signals to the ECU.

 

[doug]

When I installed my FMIC, my lbs/min readings went up almost 4 lbs at roughly the same boost pressure. My guess is that's what caused your fuel cut-- a more efficient air path that now allows better airflow through the system. Especially given that your MAF is after the intercooler, your airflow may now be high enough for the ECU to trigger it.

 

[steve]

The stock fuel system simply will not support enough air flow for you to hit fuel cut

I'm not sure what your getting at Bruce. If everything was stock you wouldn't hit fuel cut. But with a EVO III on a 2G and a FMIC you can easily push enough air to both run out of fuel from 450s and hit fuel cut.

I'm afraid the real (for now) solution to the posters problem is going to be bigger injectors so he can lie to the ECU about the air flow and avoid hitting fuel cut for a while longer. Then he'll need either chip of DSMlink to disable fuel cut entirely.

Steve

 

[oldman]

I'm not sure what your getting at Bruce. If everything was stock you wouldn't hit fuel cut. But with a EVO III on a 2G and a FMIC you can easily push enough air to both run out of fuel from 450s and hit fuel cut.

I'm sure he is capable of running out of fuel, isn't that different than fuel cut as you have taught me in the past that fuel cut is trigger by air count not fuel starvation?

 

[steve]

that fuel cut is trigger by air count not fuel starvation?

Yes. And you, I, Doug, and the poster can push enough air by turning the boost up to trigger fuel cut. The difference is three of us don't have fuel cut triggers in the code anymore.

It would be interesting to see some logs here but I'm still betting he's >100 IDC at 16 psi and leaning out. That's an aside to FC question.

Steve

 

[oldman]

The difference is three of us don't have fuel cut triggers in the code anymore.

Thanks for reminding me, more reason for a leak test.

It would be interesting to see some logs here but I'm still betting he's >100 IDC at 16 psi and leaning out. That's an aside to FC question.

Agreed, possibly mistaken bogging with FC.

 

[shallowshowcase]

ok i turned the boost down to 13psi and without tuning did this log so i can kinda start back from scratch, its way off as my timing is horrible, this is only pasting the WOT part of the log, and again i didnt tune it for the 13psi just so i wont mess completely up cause obviously i got off on the wrong foot somewhere

Time, RPM, Speed,Timing,TPS
00:05.69,2328.0, 16.0, 13.0, 100.0
00:06.30,2692.0, 19.0, 16.0, 100.0
00:06.94,3104.0, 21.0, 11.0, 100.0
00:07.55,3612.0, 25.0, 10.0, 100.0
00:08.19,4208.0, 30.0, 0.0, 100.0
00:08.84,4824.0, 30.0, 9.0, 100.0
00:09.46,5368.0, 35.0, 10.0, 100.0
00:10.10,5944.0, 41.0, 11.0, 100.0
00:10.72,6376.0, 47.0, 14.0, 100.0
00:11.34,6808.0, 53.0, 14.0, 100.0


do i need to lean out the lower rpms and richen up the higher ones

before turbo swap it would start at like 5 or 6 and raise steadily to like 17 on my timing

 

[steve]

Time, RPM, Speed,Timing,TPS
00:06.30,2692.0, 19.0, 16.0, 100.0
00:06.94,3104.0, 21.0, 11.0, 100.0
00:07.55,3612.0, 25.0, 10.0, 100.0
00:08.19,4208.0, 30.0, 0.0, 100.0
00:08.84,4824.0, 30.0, 9.0, 100.0
00:09.46,5368.0, 35.0, 10.0, 100.0

Ouch, anybody think that looks like knocking?
Please include IPW or IDC also.

Steve

 

[shallowshowcase]

answer my question from the log please


what is IPW or IDC

 

[tstkl]

Yes. And you, I, Doug, and the poster can push enough air by turning the boost up to trigger fuel cut. The difference is three of us don't have fuel cut triggers in the code anymore.

It would be interesting to see some logs here but I'm still betting he's >100 IDC at 16 psi and leaning out. That's an aside to FC question.

Steve

i always thought your injector duty cycle couldnt be over 100, do you mean his injectors are less than 100% and hes hitting fuel cut....

could it be possible that the fmic making the air colder (denser) caused the fuel needed to be higher without him upping the psi... i always thought volume and pressure were different, which is why different turbos at the same psi make different hp....

i am correct in thinking that the only changes you made were the fmic right? no increase in psi or any other mods...also, you have stock 450cc's with a 255 lph pump right?

edit: dunno where i saw 255 from... either way it doesnt matter cuz i got the right idea... the 190 and the 255 would flow the same fuel in this case...(that amount being more than enough for anyone wanting a numerical figure...)

 

[shallowshowcase]

190 fuel pump with 450s, wanted to get a good tune at a safe boost level before putting in the 660s

 

[tstkl]

well the two hoses connecting to my intake pipe are just hanging, i didnt hook them back up, is that a prob...

i guess i had my 15psi tune maxed out and upping it to 16 was the straw that broke the camels back, i turned it back down and am re-evaluating my tune with the fmic, and looking for boost leaks, thanks agian

can you just take a pic of your intake so we know exactly what your talking about (a pic is worth a thousand words...) as for the stock car not hitting fuel cut... did it at 18 psi with everything else stock... just an mbc...(note to anyone thinking about this... its retarded... dont do it... you get a LOT of knock,... then fuel cut...great on the motor....)

 

[steve]

answer my question from the log please

Sorry, I can't. Not enough data.

what is IPW or IDC

Injector Pulse Width and Injector Duty Cycle.

I always thought your injector duty cycle couldn't be over 100%

The injectors can't break the laws of physics but the ECU can ask for more fuel than there is time to deliver. What the logger reports is the IPW calculated from corrected airflow and the fuel map enrichment, that can result in requested IDC > 100%.

You can also see fuel cut by watching the IPW. If it goes to 0 while RPMs are high and TPS is high then you know for sure.

Steve

 

[steve]

As for the stock car not hitting fuel cut... did it at 18 psi with everything else stock... just an mbc

That's not exactly stock at close to 2x the factory boost.

Steve

 

[tstkl]

That's not exactly stock at close to 2x the factory boost.

Steve

just putting it out there that the stock components (cuz you would get the same results if you just took the hose off the wastegate...) can cause fuelcut... so its not farfetched that a e16g at 16 psi can overrun the stock fuel system (or in this case it would be injectors...)

 

[oldman]

as for the stock car not hitting fuel cut... did it at 18 psi with everything else stock... just an mbc...(note to anyone thinking about this... its retarded... dont do it... you get a LOT of knock,... then fuel cut...great on the motor....)

Years ago when I broke the actuator hose while installing a 3" intake, my 16g was was hitting 25 psi without hitting fuel cut though it was bogging real bad probably due to timing being pull, was young and stupid back then and actually thought it was cool that I was boosting 25psi. Years later, still young and stupid, in dealing with boost creep after fmic install, I was hitting fuel cut at about 22psi with the same turbo. Hooked up a leak tester and found 8 leaks, 3 of which were huge. This is why I think it's pretty hard to hit fuel cut unless there are external forces which artificially increases the air count in a short amount of time like boost leaks, defective maf or run away boost. I could be wrong though because I never was brave enough to boost over 20psi to see if I would still hit fuel cut after I fixed the leaks.

 

[oldman]

so its not farfetched that a e16g at 16 psi can overrun the stock fuel system (or in this case it would be injectors...)

Again, fuel cut is not triggered by running out of fuel.

 

[tstkl]

yea, when i first installed my mbc i used a spring that was too long and boosted to about 22 psi before i hit fuel cut... but i think that was just the ecu reacting slowly since i did that downhill in first gear (fastest way to check your psi... since there arent long strips around here, but its also bad since boost increases with engine load, and in higher gears your boost will be higher...) my guess is this was during a new jersey summer, where the air is no where near dense....although i could be wrong...i think steve probably has a better idea about what was going on there than me...

 

[tstkl]

Again, fuel cut is not triggered by running out of fuel.

yea, its when the ecu thinks the fuel system cannot support the ammount of air flowing into the car, i know... but since hes using stock injectors, my guess is that the ecu's thoughs are pretty close to dead on...although i dont know if the stock fuel pump is enough to get the injectors to 100% idc, i figured they would have that be the case since it seems pointless to have a pump that cannot supply your injectors fully...