dr_jones

iTrader: (1)

I've got a boost tapering problem - before you just go onto the next post - as I know there are a million + 1 posts on low boost probs (and I've read most of 'em)- have a read - I'm really stuck on this one:

2 weeks back I was running 1.3 bar boost steady up to gone 6.5K rpm - usually with an initial spike of 1.4 bar - obviously I was well happy with the performance.

I fill my car ('97 STi v-ltd jap import) up with Shell Optiimax - drive to the airport nice and steady and go off on holiday - my sis drives the car home - where i'ts then laid up until my return some 2 weeks later.

When I return - I realise to my horror - that my much missed Scoob has lost a little of it's sparkle - my boost now spikes to 1,4 bar and then tapers to 1 to 1.1 bar by 6.5K rpm.

Imediately I think - bad quality fuel! - so I drain down the tank and fill up with my regular: BP 97 octane (yes I know "Optimax" should be 98) - reset the ecu and...... absoulutely no difference.

I know all about the solenoid jamming problem so nex ton the list is Solenoid cleaning - solenoid checks out fine but I clean it anyway - reset the ecu again and again no difference.

Next I wack in some +2RON octane booster - reset the ecu and still absoulutely no difference.

The Last think I've now tried is STP Injector cleaner - the thinking being - maybe I got some crap in one of the injectors so I'm simply running lean at high boost - I'm now over half way though cleaning cycle (1 tak of fuel) and thinks are looking remarkably like they ain't getting any better.

This W/E I'll replace the plugs as a matter of course btu I'm sure this'll not help at all.


BTW only mods are air filter / possible ecu upgrade (need to check out serials but as I remember the box and the boards no's didn't match.

Has anyone got any ideas as to what could possibly be causing my issues?

john banks

It was colder 2 weeks ago but I think you are looking at an ECU or actuator/wastegate problem. Low octane doesn't usually cause low boost, just causes det at high boost. Spark problems usually cause misfires rather than low boost.

dr_jones

iTrader: (1)

OOOh - I was worried about the ECU possibility.

Thought the ECU was "intelligent" to lower the boost at the onset of Det though - thats the whole reason for the reset that so many owners swear by?

john banks

I don't think the ECU is faulty that is not what I mean, but I am unaware of any Subaru that runs that much held boost as standard!

dr_jones

iTrader: (1)

OK - I see what you mean - from waht I understand now the ECU retards the ingnition when it detects knock rather than dropping boost - still on a bit of a leaning curve with the scooby - I come from a Saab background....

Anyhow - I've run the diagnostics on the ECU - no faults reported.

Also checked base boost - approx .065 bar - seems fractionally low - I beleive it should be 0.7bar? - don't think that should cause that much difference...

Also checked wastegate shuts correctly (by disconnectiong pressure line and being VERY careful) seems to be OK - boost rises above normal levels.

I'm thinking the next step will be cleaning all boost related connectors as the salty condidtions of late may have caused som corrosion and so potential MAP sensor errors etc etc.

Any other ideas?

john banks

yeah, your ECU is probably aiming for 1.1 bar hence why it doesn't hold?

Jolly Green Monster 2

Mine was doing similar when I had a leak on my boost gauge connections..

I run less boost so difficult to tell how similar but was boosting to .9bar and backing off to .7bar... now I fixed the leak it hold .9 9 times out of 10.

Just worth checking for leaks on all you pipes..

JGM

dr_jones

iTrader: (1)

Yeah I'd better do that this W/E.

Maybe I had some sort of leakage or other problem before and that was allowing the 1.3 bar.....

It's just irritating as I'm set to install my W/I system but don't want to until I get this resloved.

Anyone know if it's possible to identify ECU part no agasinst boost target?

Dizzy

I think what John means is how are you maintaining 1.3 bar boost? Stock ECU's dont run at that do they? Have u got a remap/dawes/Boostr ctrler?

Maybee you've still got your sunglasses on and can't see the boost gauge properly

dr_jones

iTrader: (1)

LOL! - No really it was maintaining 1.3 bar (dyno'd at 298 bhp / 260 lbft at Power Engineering - the dyno chappie was pretty impressed I think considering the car looks totally standard - and I was pleasantly suprised......)

The cars an import from Newera and I'm fairly sure it's had a re-map of some sort - thing is I havn't got any history on whats been done to the ECU - at present all I know is the Serial on the Box does not match the serial on the board - but like a dumbass I've lost the bit of paper I wrote to No's down on - I'll dismantle again at the weekend and take photo's this time - maybe someone'll recognise whats fitted?

I'd like to find out more on the ECU to see if it's remappable or not (if thats normal)

Suprisingly - today the boost has crept back up again to 1.15 - 1.2 bar held up to 6.5K ish - doesn't look very stable though - the needle tends to drift up and down by .5 - .1 bar - I'm SURE there's some sort of problem - tearing my hair out trying to track it down.....