94 Legacy GT running rough/low boost

[Legacy_GT]

Hi all,

I have a 94 Twin Turbo Legacy which is running rough and has low boost (about 7psi). Its very hesitant and feels really laggy when under boost. Have reset the ecu (running a Prova ecu) and it will run good for a couple of minutes but has a sharp jolt every now and again, then it will drop back to the usual. Also the engine note will change sometimes when i change gear and have to wait a couple of seconds for it to sound normal or theres lots of lag. Have tryed running it on 98 but it makes no difference. Have taken it to 3 different garages and they cant seem to find the problem. I have tryed so many different things but im running out of ideas now as to why its running crap, its also throwing no codes. Heres a list of things ive had checked/replaced.

Tryed another ECU

Changed AFM (tryed 3 different ones)

New O2 Sensor

Checked all vacuum lines.

Checked all hoses

Changed differential pressure sensor

Coil packs checked (1 replaced)

Plugs checked (fairly new anyway)

Primary turbo removed and checked (wastegate replaced on it)

Any help would be much appreciated, ive spent too much money on it and not geting anywhere . Just want this thing to run mint again!

[Guest boostin]

Have you got the correct AFM in there? You may have tried 3 of the wrong type.

[Legacy_GT]

 boostin said:

Have you got the correct AFM in there? You may have tried 3 of the wrong type.

Yeah all blue sticker ones, made sure they have the same numbers

[Guest boostin]

The engine note change is it switching to twin turbo or secondary mode.

What is the TPS set to at idle? Mine was set too high and caused a few similar issues, one of which was switching to secondary way too early.

[Legacy_GT]

 boostin said:

The engine note change is it switching to twin turbo or secondary mode.

What is the TPS set to at idle? Mine was set too high and caused a few similar issues, one of which was switching to secondary way too early.

Not sure how to tell what the TPS is set at but the car usually idels normally (around 800rpm). Every now and again the car just about stalls when its cold though.

[Guest boostin]

So it used to run fine? With the Prova ECU? And it just one day started running rough with low boost?

[Guest]

Are you in Christchurch by any chance? 8)

[Legacy_GT]

 boostin said:

So it used to run fine? With the Prova ECU? And it just one day started running rough with low boost?

It was running fine when i put the Prova ecu in, however i had a bit of an incident on the motorway. Ran over some sort of metal pole with a piece of metal sticking up out of it, which broke a weld just after the downpipe and tore my resonator. Have had it all fixed but it sounds like theres a small leak coming from somewhere, but can only hear it when parked or driving near a wall or fence. Was told it was normal and theres no leak but im not too sure. Since that incident happened the car has started to have problems, not sure if it was a coincidence or not. However ive had the car for about 4 years and it would run good then the boost would drop back to 7psi for a while, then would run good again. Its been very annoying .

[Legacy_GT]

 liquid_ice said:

Are you in Christchurch by any chance? 8)

Im in Welly

[GravelBen]

Checked wiring, connectors etc? I'd be wondering if the impact from running that thing over also knocked something else loose.

[Durty-Sanchez]

- Whats your intake like? Those flexi-corrigated plastic intake pipes start to tear around the ends... mine had a gash and was leaking badly, took me 4 months and a new set of coils to find the bugger! Sharp jolt sounds AFMish, but a loss like that should store a fault code.

- Coilpacks would be my next bet... they can test them all they want but i'd only ever replace entire sets of 4. If ones bad enough to fail a test then the rest are probably just as old and worn.

- Still have factory BOV?

- TPS as mentioned, although it's still metered air so shouldn't be as jolty as you describe

- Possibly a solenoid in the BBoD, you never really know with that thing

Is it consistently repeatable? Or does it just *happen* sometimes while boosting? If it just *happens* i'd go coils or unmetered air

[Legacy_GT]

 Durty-Sanchez said:

- Whats your intake like? Those flexi-corrigated plastic intake pipes start to tear around the ends... mine had a gash and was leaking badly, took me 4 months and a new set of coils to find the bugger! Sharp jolt sounds AFMish, but a loss like that should store a fault code.

- Coilpacks would be my next bet... they can test them all they want but i'd only ever replace entire sets of 4. If ones bad enough to fail a test then the rest are probably just as old and worn.

- Still have factory BOV?

- TPS as mentioned, although it's still metered air so shouldn't be as jolty as you describe

- Possibly a solenoid in the BBoD, you never really know with that thing

Is it consistently repeatable? Or does it just *happen* sometimes while boosting? If it just *happens* i'd go coils or unmetered air

Ive already replaced the plastic intake pipe since ive owned it, looks good from the top but ill take it off tomorrow and check the underneath and around the ends. The sharp jolt randomly happens under light and heavy accelleration and its like a complete loss of power, a bit like boost cut but regains power straight away.

The coil pack that was replaced was cracked and chipped..dont think they have been tested yet.

The BOV is aftermarket and has been tested for leaks.

Could a faulty knock sensor cause the jolts?...im thinking it could be causing the low boost and increase in fuel usage but mabey both problems?

[Guest boostin]

Who have you had check it?? Might be time to spend some pingas and have it checked over by a Subaru agent.

[Durty-Sanchez]

Chipped and cracked coils? My money's on the coils being the culprit here... if you like I have a full set that are 4 years old. I've already set them aside for someone else, but you're more than welcome to try them out to see if it improves your problem. If it doesn't then at least you know you dont need to fork out for new coils!

I'm in welly, PM me if you're keen.

Fuel pump's another one worth considering (if you haven't done it already). Could be running out of steam at this age, which is a very common problem. Knock sensor going stupid will pull the timing and put the ECU in to safe-mode. Does the knock sensor CE code come up? If you like I can have a listen to the knock sensor to see if it's poked or not if/when you try the coils.

[Legacy_GT]

 boostin said:

Who have you had check it?? Might be time to spend some pingas and have it checked over by a Subaru agent.

Sorry for the late reply been busy as. Have had it looked at by subaru in lower hutt a couple of years ago when they were around and they were useless. Never fixed any of the problems and tryed to say i was running it on the wrong gas, but was always run it on 98, wasted around $500 there. Also taken it to Speedtech, they told me there was nothing wrong with it and there was a slight miss. Cost me $170 and a free chocolate bar...$170 chocolate bar!. Also taken it to Mendoza Mechanical, they didnt know what was wrong with it and replaced the 02 sensor, they were trying to say it was throwing that code but it wasnt so i ended it there before they started replacing part by part, cost $400 there. Just hoping someone from these forums could help me fix the problem, i dont mind paying them as long as they can diagnose the problem. Any help would be much appreciated!

[Legacy_GT]

 Durty-Sanchez said:

Chipped and cracked coils? My money's on the coils being the culprit here... if you like I have a full set that are 4 years old. I've already set them aside for someone else, but you're more than welcome to try them out to see if it improves your problem. If it doesn't then at least you know you dont need to fork out for new coils!

I'm in welly, PM me if you're keen.

Fuel pump's another one worth considering (if you haven't done it already). Could be running out of steam at this age, which is a very common problem. Knock sensor going stupid will pull the timing and put the ECU in to safe-mode. Does the knock sensor CE code come up? If you like I can have a listen to the knock sensor to see if it's poked or not if/when you try the coils.

Thanks man, its worth a shot. Pm'n you.