WRX STI V8 Surging When On Boost

[Steveo]

Hey guys,

First of the cars a 2003 WRX STI NZ New only done 60,000kms, when on boost in say third gear it seems to surge not really bad but definatly noticable. Not the cars pretty much stock standard, all thats been changed is a GFB BOV (which was fitted by previous owner) and the end muffler changed same thing though prior to me owning it.

I\'m thinking it might be a fuel pump? Or maybe pulling timing because I can only get 95 where I live, but it doesn\'t do it all the time. Any suggestions will be helpfull.

Cheers

[Pappu1]

stock boost?

does the engine check light come on?

try filling 98 and see if does the same?

can u tighten the bov (if adjustable) and retry?

[Guest]

Bov wont effect it if its surging coming onto or on boost.

Big difference between pulling time because of knock and compressor surge. Any chance of a video?

[Marky]

Could just be a misfire - its hard to hear them on soobys

Any number of things but the car can tell you to a degree - where are you in the country

[Pappu1]

i have seen the bov open on partial throttle comming on boost in some situations (that was on my old v7 sti with a gfb 50/50) - with partial throttle i cud get bov to open in certain type pulls ...once we tightened the spring a bit it didnt

also that was trying to make it happen and didnt just happen on regular driving but OP didnt say what sorta driving or throttle % usage when this happens

also yea cud be surge as but that only happened on some fmic ones with open exhaust ones that i have seen (and only after a bit of tune - didnt happen on stock tune tho)

[Guest]

 Marky said:

Could just be a misfire - its hard to hear them on soobys

Any number of things but the car can tell you to a degree - where are you in the country

V8 sti easier with EL headers.

Wouldnt expect comp surge on stock setup but who says it hasnt had a tune? Any way to tell? Op said on boost in 3rd.

[Pappu1]

never heard of surge on stock tune in the ones i have done

same setup stock vs tuned setup and the tuned one had some surge appear ...scared the hell outta me and we just backed it off a bit

[ben-jamminn]

I had surging issues with my V7, turned out to be the AFM

[Guest]

Depends what sort of surge hes getting - the feeling or the noise. AFM can get out of spec enough to not throw a light but still make the car feel like it stutters a bit under load even slight load. Im picking its not comp surge but more the feeling. AFM or Knock sensor.

[Steveo]

Definatly in the feel and not noise, its like it\'s loosing power then coming on and off boost not really bad but enough to notice I would say more when under load. Doesn\'t seem to do it from a stand still and running up through the gears. It\'s a bit weird just enough to be annoying. Last night the temps were -2 degrees so thought it would be running really good.

Would love to run it on 98 but nearest station is over 2 hours away. Guess I go get it plugged into diagnostic gear and go from there, just annoys me as most of the time they just start replacing sensors with no real idea on whats going on (past experiences). Just thought it might be something common, bov doesn\'t seem to be adjustable and seams to seal from what I can see and hear, would like to try a stock BOV to rule it out though.

[Steveo]

Don\'t mind paying the money to fix it whatever the cause, I thought AFM\'s don\'t throw codes and the only way to test is with a good known unit. Have no boost gauge so can\'t really tell whats going on with boost levels etc.

[Guest]

I would say afm or knock. What about slow steady accelerating up a hill from low revs? Worse when the cars not up to temp? Later cars dont really perform way better on a cold night like old cars do as theyre managed a lot better and you probably have a AAT and IAT on your car so the ecu has a pretty good idea of what its doing. Is it getting worse?

[Marky]

They put out a code most of the time, but if they\'re a bit "off" you can just get average running without the car thinking anything is wrong

You could buy a diag cable online and DIY it with a laptop? they\'re pretty cheap and the car can tell you a lot

Could be any number of things to be honest - could be AFM, could be another sensor playing up, could be a leak which only shows up sometimes - could be an actualy problem with boost levels (I know a few guys on here have found a fault which relates to the knock sensor and boost going notmuchLOTSnotmuchLOTS)

P.S this isn\'t talking about "compressor surge" but the car just surging in acceleration - like not even power - right? Technical terms a bit swappable

[Marky]

 evowrx said:

I would say afm or knock. What about slow steady accelerating up a hill from low revs? Worse when the cars not up to temp? Later cars dont really perform way better on a cold night like old cars do as theyre managed a lot better and you probably have a AAT and IAT on your car so the ecu has a pretty good idea of what its doing. Is it getting worse?

They\'ll still go better in cold than hot though

[Steveo]

Yeah well thats what I was thinking, couldn\'t really understand why it would do it when it was cold outside / hot I could understand a bit more.

I know my Silvia used to run higher PSI in really cold temps, could it be hitting factory boost cut? Seems a bit strange though.

[Steveo]

Yeah surging like in acceleration (seat of the pants feel), might just take it into Subaru and see what they recon don\'t really want to mess with it to much myself.

Just thought it might be something simple, but yeah it\'s very hard to diagnose over the internet lol.

[Guest]

 scottspeed said:

to plOx, most road cars are fine with only ACT because they are not tuned to the edge. But on a race car which may be .5deg ignition away from detonation or even 1 deg into detonation, a slight change in airbox temp can have a huge effect on the engine.

When you have the time the factory does and resources, by using both sensors they end up with a more fuel efficient car with a constant power range over a wider range of temps. Older cars would always go good on a cold day/night whereas this isnt felt so much on newer cars.

[Pappu1]

a running scan is better than a static scan tbh

if u were in auckland we could have met up and done a bit of logging etc..

plz dont throw sensors at it in hopes of fixing as thats just a very expensive way to fix things and sadly true that a lot of the workshops will do that

pisses me off at times when i hear of such stories

u cud try afm cleaner in the meantime..usually works if its minor dust issues...not that uncommon...

[Steveo]

Yeah I\'ve been down that track before with a Legacy, a workshop who I used to trust replaced AFM, knock sensor, coil packs. Apparently they were chasing the fault around the engine bay (their words). This is a long time ago, not taken for a ride so easily now, just wouldn\'t think I would be looking at replacing sensors with only 60,000km\'s on the clock and definatly hasn\'t had a hard life.

Cheers for the offer but couldn\'t really be futher away, bottom of the deep south. Might give AFM cleaner a try.

[Pappu1]

here is hoping for a good result..

also see how much boost does it surge at?

is it only 3rd gear at that same boos/rpm?

can u repeat it in say uphill or flat?

basically get more info on when it happens?

[Steveo]

Will do some more testing over the weekend, is octane boosters alright to use just want to rule DET out? Heard mixed storys about them.

Definatly only does it under load, for example 3rd gear pull from 50k\'s. Kinda like my Silvia used to do when it had a stuffed coil pack and could only pick it up under load, but not the bad miss like that though.

[Pappu1]

if its load only then cud be coil/spark

does it surge all the way till redline or only between certain rpm?

also an important question

if u dont load it and just as smoothly get the rpm up, does it do it - like maybe downhill boosting lol

[Steveo]

Well when I noticed it doing it I stopped on a straight flat piece of road, and held it flat right through the gears and it went fine. It\'s kinda life it\'s coming on and off power right through to redline. But not drasticly I mean if you didn\'t know you probably wouldn\'t noticed it.

[Guest]

Ignition breakdown miss doesnt really feel like a surge/stutter tho. Ive had a coil pack go where the car just started progressively more running on 3 took about 10min but I couldnt stop needed to get home. Also had one go slowly (wasted style) that slowly started to hit cut sort of like boost cut in the end any load at all it just sounded sorta like it was bashing its head against a wall.

[Steveo]

Yeah I definatly wouldn\'t say its a coil pack, least this is helping to point me in the right direction though I\'m quite keen on getting some Process West stuff soon TMIC and their fuel pump/surge tank setup. So don\'t want to do the fuel pump till then if I can avoid it.