Boost Cut - what causes it?

[naughtika]

hey guys..I know most of you have had experiences with forced induction.. as for me, this is my first car with FI..

just wanna know few things about boost cut..

what are the possible causes of it?

- Over boost
- under/over fuelling?!
- would heavily stepping on the accelerator whilst the turbo is spooling/starting to kick in cause boost spike too?

reason I ask.. I am often hit boost cut, even though i turned down the boost to around 9 psi, even on hot/warm days.. and what's funny is.. when at night, where it's more colder/cooler when i thought when boost cut would kick in..

any comments? ideas on what i should do to eliminate this problem?

last thing.. would this damage my engine in a short period of time?

 

[bradc]

the air flow meter measures the amount of air going past, when you up the boost, it obviously lets more air in and you can very easily get to a point where the stock ecu thinks to itself hand on a minute, he is flowing xyz air at abc rpm, this isn't right, something is wrong, and then it cuts the fuel.This will happen more in colder weather because the air is more dense, with a big intercooler (same reason), and better flowing pipework, more upgrades, etc.In saying all that though, 9psi is quite low, considering how hot it will be in Queensland at the moment, most people run into it at 12-14psi.When does it occur exactly? lowish rpm? Is it really abrupt and severe, and feels like the engine has just exploded, or is it more subtle, kind of like it has just lost power for a tiny bit and missed?

 

[Guest]

boost cut happens around 14-15psi on our cars,

are you sure its boost cut?? its like hitting a brick wall,

shitty spark plugs cause a similar issue, (miss fire and loss of power)
they need to be gaped at 0.6 - 0.8mm,

 

[naughtika]

well.. when it happens it feels like the engine just died for that moment, so i'd have to let go of the accelerator..

well my odometer's nearly 93k so i guess i would have to change them soon.. any brands you guys recommend?

for now i'll take the MBC off til i replace the plugs and all..

 

[bradc]

yeah possibly plugs then. What point in the rev range does it happen?

 

[Guest]

i use NGK iridiums,

bkr7eix (1 colder than the factory plug, witch is the 6eix)

 

[naughtika]

it happens around 4500rpm, but sometimes around 5500rpm

so most probably its the plugs.. i used NGK Iridiums too for my previous car..

hopefully its the plugs..

 

[bradc]

defo plugs then!boost cut typically happens at 2500-3000rpm

 

[naughtika]

hey everyone.. guess what.. the other night I hit boost cut again..

this time was around 3500rpm when I quickly floored the pedal.. car was fully loaded with some groceries and people.. (1x 50kg woman, 2x 100kg fellas and me)

currently have set the MBC at 9-10psi.. AFC's connected but not fully tuned.. also I've changed the plugs and definitely gapped them at .8mm and replaced the panel filter with a new one..

can somebody please enlighten me on how to solve this on going issue?

 

[Guest]

Did you see what the boost spiked to at the time

 

[naughtika]

nope, i was concentrating on the road... trying not to sideswipe other cars...

 

[Guest]

It's likely that it spiked and caused the fuel cut. I get the same even with my ebc with the cold weather we have over here just now but it logs the highest boost so I can check later

 

[naughtika]

seems like you can sort out your issue quicker than me.. it was raining when it happened... so I guess the cold weather + stock exhaust + bigger cooler didn't really help as much..

 

[bradc]

see if you can watch for it's spike next time, it might be spiking quite high.

 

[Guest]

prolly related to ur FMIC dude ... it would get worse if u had the exhaust done.

 

[naughtika]

prolly related to ur FMIC dude ... it would get worse if u had the exhaust done.

please don't say that

 

[bradc]

it's actually not a bad thing.

the more mods you have that help to get cool air into the car, such as intercooler, exhaust, boost, air filter etc will get the ecu closer to the point where it sees so much air that you have boost cut.

IE if you have boost cut at 9 psi with a whole heap of mods, and you used to get it at 15psi when your car was stock, that means that now at 9psi you're moving as much air as what you used to when you were at 15psi.

 

[Subaru ETA]

take your manual boost controller out and try it

 

[naughtika]

took the MBC off for the time being.. then took it for a decent run..

now Im getting MORE engine hesitation.. not huge ones like the way I was explaining as earlier..

it now happens when Im on boost.. It still has power but you can feel the constant hesitation..

 

[bradc]

spark plugs or leads or something else borked!

Boost cut is apparently like you've hit a brick wall and it feels like something has just broken and it's going to be expensive.