boost problems 15psi/7psi

[mikenfee]

Im running a standard v7 wrx apart from exhaust and i am having boost problems, it runs 15 psi normally then all of a sudden it decides to run 7 psi for a while then goes back to 15 psi, any reason for this? I have recently had to replace my afm and o2 sensor but this problem has been happening for the whole 3 years i\'ve owned the car, any ideas on the problem would be greatly appreciated, cheers

[lachlan]

ecu will be detecting something somewhere and limiting boost .

could it be that its not up to temp yet ?

shitty fuel and deteting knock ?

not sure for the reasons .

i know where to find the list of reasons for a nissan . not sure on subaru

put a boost controller on it ;D

[mikenfee]

def up to temp, still happens 2 hours into a long trip, possible shit fuel, i always run atleast 95 bt maybe its nt enough and mite have to run 98 all the time, i have heard of the wastegate actuator getting stuck on early wrx\'s but unsure if this could also be something to look at

[ebg5 NZ]

@mikenfee I get this issue too at times, ~12psi normally then at any point during my drive (every few days-ish) it\'ll drop to 5. I always use Z 95 fuel

Most of the time if I cycle through the gears at half throttle, at some point during that it\'ll boost like normal again.

[mikenfee]

yeah, its really annoying, mine usually goes to 7psi just when i want the power e.g passing a evo lol and then clears when im just cruising, would like 2 sort it

[Timmah]

This issue came up a while ago. It ended up being the knock sensor being poked that was causing the boost issues.

I\'d suggest taking it to a mechanic who might be able to better pin down the problem, however: http://www.subaruspeed.co.nz/products/new-knock-sensor-legacy-199803 that\'s the knock sensor you want.

[mikenfee]

cheers 4 that, does the knock sensor not come up as a fault? just had the obd2 scan dun and nothing came up?

[Timmah]

 mikenfee said:

cheers 4 that, does the knock sensor not come up as a fault? just had the obd2 scan dun and nothing came up?

ECU may still think the knock sensor is giving correct readings. It was the case in the other thread too. I\'ll see if I can find it.

[Pappu1]

What part of country u in?

Does the Check engine light flash?

When on boost does it hesitate?

[mikenfee]

in the wairarapa, no check engine light and it doesnt seem 2 hesitate, just decides to run at 7psi instead of 15psi, exhaust note seems 2 change a bit when this happens which i assume is coz there not enuf boost 2 open wastegate

[ben-jamminn]

Try knock sensor

[Stoffa]

replace the knock sensor ;D

[ben-jamminn]

my thread http://www.clubsub.org.nz/forum/index.php/topic,32969.0.html

I was having all sorts of issues with my V7, surging, power dropping off, and the same boost issue as you are having (turned out to be the AFM after all) but I was also advised to change the knock sensor. So if you\'ve already done the AFM (I assume it was for a new or known good one?) then it\'s worth a shot.

Better still, find someone who has a laptop set up with RomRaider software and a tactrix cable. They can then datalog your car and diagnose a fault much quicker and without wasting time replacing parts

[mikenfee]

cheers that sounds like a go

[reaperblitz]

*Did this to me when I was boost spiking due to modded exhaust.

Had to get an ebc and sort waste gate opening too fast -" gain" to stop from climbing too high.

Could be this?