Turbo_Steve

Getting pretty annoyed with my car: It is highly likely to be wrapped around a tree at present out of sheer frustration.

Car drives very nicely in the summer. Come winter time (cooler air, denser charge, more boost) I slam into the fuel cut in pretty much every gear if the temperature is 0 degrees.

This has been a problem for over a year now (it goes away in the summer time!) and looking at boost readings, the pattern is typically that the car will mske 1.1-1.2 Bar (off the scale of the boost gauge, so cannot be sure) at aboout 4500RPMs. Then, I guess the ECU sees the overboost and bleeds it all off to about 0.8Bar by 5500RPMs If it is a cold day, it looks like the ECU sees a bit more boost (maybe 1.25Bar), panics and cuts the fuel.

My first thought is to clean the boost solenoid, but as it appears to be bleeding correctly under an overboost situation, does anyone have any ideas?

Mods: ITG airfiler and airduct into bottom of airbox for better induction. Everything else has been taken off in order to try and solve this issue.

STi wanna Subaru

iTrader: (1)

Model year? Any other mods?

john banks

Clean it. It can still do the behaviour you describe. I don't want to bore you with why and don't have the time to type it.

If it still does it, time to fiddle with restrictors or a restrictor valve which will sort it - assuming your actuator is working fine and not leaking.

Turbo_Steve

Thanks.
Would not have been bored, but I know your time is precious. (Hey, so is mine)

I didn't think cars with 3-port solenoid HAD a restrictor?

Tell you what: it feels dead fast at 1.1 - 1.2Bar. Can I have it like this all the time, please? (and no, don't worry, I am not about to run out and buy a FCD).

john banks

Yes the 3 ports do have a restrictor. Bob would keep you right and has posted before about how to sort out overboost on older models with 3 ports. I have not fiddled with them.

Turbo_Steve

Ah. Well....mine doesn't have a restrictor, cos the hose needed replacing (it had split into about 5 pieces) so that will not be helping. I suspect the solenoid needs cleaning anyways.

Thanks John. Erm....which bob are we talking about?

nom

3-port Bob Rawle, that would be

Turbo_Steve

ooooOOOOOOooooo..ok.

Pavlo

what car?
what turbo?
any chips?
what exhaust?

shouldn't be a problem to fix

Paul

Turbo_Steve

Dunno what ECU I have (can't remember) but the Car is a 94 UKLegacy Turbo (white saloon, so a turbo-taxi, not a turbo-hearse ) with an airfilter and some nice big holes in the airbox to help it breathe a lot better.
Bottom end has been fully rebuilt with MY95 WRX components.
Gearbox has been replaced.
Earth Mod.
Not much else: I would have done a lot more but I don't have access to a garage.

planned investments are:
New ABS sensor (one has failed)
New sparks / coil packs (one of these is shot, but dunno which)
New Cambelt (coming up on 100,000)
ScoobyECU
New exhaust (Had one, but never fitted it due to financial probs)
Have a forge Recirc BOV in the post
Have an AFR waiting to be fitted.
Would consider fitting a TD05 for sensible money.
Wonder how much it costs to improve fuelling.

A few hoses had to be replaced near the turbo because they split.
That's about all.

[Edited by Turbo_Steve - 12/25/2002 4:08:27 PM]

Pavlo

Well, I've never seen overboost on my Legacg when it was standard. So my first thought is crap in either the boost solenoid, or the hoses from the turbo to the solenoid, and from solenoid to actuator.

The Legacy turbo doesn't have an adjustable actuator, so it can't be that, if the exhaust is standard, it can't be downpipe flange related either.

Are you sure they put the original turbo back on and not the TD05 from a WRX? If you put a TD05 on as it is, would expect overboost and fuel cut, but probably much worse than you describe.

Paul

Turbo_Steve

Nah...I just got a new bottom end.
I am still not lcear whether or not the car left the factory with a restrictor in the actuator pipe. The original actuator pipe split, and the barb on the resonator had snapped...so I blocked the resonator hole and tee'd off from the nearest pipe, and also replaced the actuator pipe with a piece of fuel hose I had.

I suspect that the subtle change in plumbing is enough to throw the ECU's estimation of required duty cycle for the boost solenoid off, and this causes the overboosting.

On a normal day, say in 3rd gear, the boost will climb quickly at 4500rpms to 1.0Bar, and then drop back quickly to 0.9Bar and hold.
In 2nd gear (presumably the most load) on a normal british day, the boost will skyrocket straight to 1.1Bar at 4500rpm and back off to about 1.0Bar.
If it is a cold (1 deg C or lower) day in 2nd gear (this seems to be the worst gear, so I assume this is the heaviest load on the engine i.e. most boost) then the boost will climb quickly, until at 4000-4500rpms the boost will reach 1.15 or 1.2BAr, and the fuel cut will slam my head into the steering wheel.
If it is colder than this (0 degrees C or lower) then fuel cut will be experienced in every gear at WOT, usually at around 4500rpms, but can happen at anytime if trying to accelerate quickly.

I have considered just buying a dawes device, and hang the consequences as I know this will fix these problems, however I would prefer to keep the ECU in charge of everything, especially as I would like to do some modifications and re-map the ECU.

I have a rough target of 250bhp in mind, but obviously if a few little mods will give me better power (without putting the internals / bottom end at risk!!!) then I would be willing to go higher!

What do you reckon? And how far have you taken a legacy engine?

Pavlo

5th gear will give you the most problems, as it has the most load.

I'm curious to know what you did with the pip that went to the inlet? Putting the restrictor back in may well cure the problem, as the restrictor limits the boost bled off to atmosphere. If the restrictor is removed, the pressure is likely to be less for the same solenoid duty cycle.

The pipe with the restrictor (bottom one on solenoid IIRC) should be plumbed to vacuum, so anywhere before the turbo. Leaving it to atmospheric is probably going to give very similar results.

Paul

Turbo_Steve

Bottom Pipe is to Vacuum, just before resonator (Tee'd of the oil rebreather vacuum pipe).

Pipe with restrictor (solenoid to turbo) is long gone...I did not realise there was a restrictor, so it is most likely in the bin somewhere.

Hence me asking if a remap will fix the problem (which I think it should...the restrictor is just there to smooth the lower duty cycles of the solenoid, surely?)

I really need to think longer term with regards to modifying the car, you see: I don't want to waste time fixing a problem that will just go away if I re-map.

Howz christmas? Nice and drunk yet?

DGRALLYING

Hi Steve

I have the same problem with my Lego, but mine is chipped....

Have you made sure that you have the restrictor in the bottom hose coming off the Solenoid?

Turbo_Steve

LOL....DGRally.....read above!

Was discussing whether or not re-mapping will fix the fact that I DON'T have a restrictor.

ustolemyname??stevieturbo

iTrader: (1)

When you say the bottom pipe goes to vacuum.... are you sure you mean vacuum??
Correct fitting for the 3 port is,
Top small pipe, to/from compressor side of turbo.
Next one down, should go to the wastegate actuator.
The bottom pipe, pointing straight down is the vent pipe, and is normally connected into the resonating/calming chamber just after the airflow meter.
This is not a vacuum point as such. More free air, so venting this to atmos is pretty close.

Turbo_Steve

I have connected the bottom pipe to a tee piece into the oil breather line jujst before the resonator (mine is broken!).

Question: Do I NEED the resonator...it looks like it is costing me airflow!

Steve

ustolemyname??stevieturbo

iTrader: (1)

Junk the resonator

Turbo_Steve

Okay Steve...but what do I get instead?