Jay m A

iTrader: (2)

And I shat myself! The girlfriend wasn't too impressed either..

Just had the full Scoobymania system fitted on my MY95 WRX thinking it wouldn't raise the peak boost much, just spool up quicker. The thing is my boost in 5th gear went to 1.15 bar peak and dropped to 0.95 held. Now, the overboost happened in 2nd, I'd held the car at 4000rpm at a roundabout and when flooring it on the exit it cut in!! to say it unsettled the car would be an understatement and a half.

This brick wall can't do the engine and transmission any good and don't want this happening again, especially since I'm at Castle Coombe at the weekend

I thought there was less boost in 1st and second gear, so how come it didn't happen in 5th?

Is this overboost common in the older cars? Since peak was 1.0 on a good day before the exhaust mod, is 0.2+ boost increase normal?

Any advice / solutions appreciated

Cheers

Justin

MikeWood

Sounds like fuel surge to me

Mike

John H

Hi Jay m a,
It's one scary moment isn't it ! Then when you carefully put your foot back on the accelerator and hear the engine still works (and isn't spread 50 meters back down the road) ,pure releif !
This happens too on my 94WRX which is also fitted with the Scoobymania system. Don't know what boost it's happening at cos the boost gauge was fitted by the previous owner down on the lhs of the steering column. It's in a bad place for looking at if pushing the loud pedal with enthusiasm.
Soloutions ; make sure all the pipes to the boost solenoid are clean , use brake cleaner for this,
OR fit a link ECU or a unichip
OR fit a boost controller

Do a search on any of these topics for detailed explanations by folks far cleverer than me !

Regards,

Jay m A

iTrader: (2)

Mike, please enlighten me! I was very low on fuel at the time, is that a factor?

John, boost gauge? tell me about it! mines underneath the stereo in the centre console, needs passenger assistance most times. Needless to say I wasn't watching the gauge exiting the roundabout so can't be sure it got to 1.2, but judging by other peoples description of the cut out I just assumed it did.....

Thanks

Justin

phil_ng

Sounds like fuel surge to me too. Did track day at Brands yesterday and when below quarter full had momentary power cuts at Clearways (long right hander). Completely ok again when filled up. I would eliminate this possibility first. Im running 1.3 bar on STI5.

chiark

If you were low on fuel, I'd guess at fuel surge. Just to position my advice, I've never experienced it, but there was a rash of postings about many different types (from UK to STI to P1) having troubles on left hand bends when having less than 1/4 tank full.

MikeWood

Justin

As you had just cornered at 4000rpm I presume you were corning quite hard. In this situation the small amount of fuel you have in your tank is all sat at one side ie away fron the pump. Then you hit the throttle hard and it all moves to the back, again away from the pump which eventually runs dry. No fuel pressure = no power.

The worrying thing is that just before it stops it must have run lean as well. High revs, lots of boost, leam mixture, possible detonation?

This will happen very rarely on the road but you should expect it when low on fuel, particularly on long fast roundabouts.
On race circuits it can happen even when the tank is over half full if there is the wrong conditions like you would get at somewhere like Silverstone where it's possible to corner at very high g levels for long periods of time.

Mike

NITO

Mike,

Do Prodrive do a mod to counteract this, ie baffled fuel tank or something which they can sell to people with road cars (and if so how much?). It happened to me the other day too with over 1/4 of a tank...usually I'm expecting it when I'm below the quarter tank mark so I'm more careful when chucking it round roundabout exits!

Thanks
Nito

MikeWood

Nito

It doesn't happen on a WRC or Group N car with an FT3 tank, but do you really want to put all that kit into the back of your car.

It's much easier to put more fuel in!

Mike

NITO

Mike,

It's certainly much cheaper to put more fuel in (although not even so sure about that now )but it's still a pain when it happens!! Potentially dangerous too!

Perhaps an FT3 WRC/gpN tank is overkill though and I'd have to lose my Sub but there is still this issue;

Quote:
"The worrying thing is that just before it stops it must have run lean as well. High revs, lots of boost, leam mixture, possible detonation?"



Nito
Perhaps I need to fit a fuel below half tank warning light to add to the collection

Jay m A

iTrader: (2)

Mike,

Thanks for the response, apart from the running lean / det bit, did tou have to say that?

I do hope its fuel surge, easier to fix than overboost!

Justin

Bob Rawle

It is more likely to be overboost, the downpipe will have pushed the peak boost up, not too hard to solve, just need to adjust the restrictor size in the solenoid vent pipe, 4k in second is not exactly pushing it and it didn't happen until you accelerated going off the roundabout. Sounds like you could have hit the "sweet spot", the TD05 turbo really can spool if its caught right.

Bob

Jan Shim

Someone once said restrictors are dangerous things to play with.Here's my experience with what works for my overboosting problems. I run a 3-port solenoid with my standard ecu and 4mm hoses to the turbo outlet, wastegate actuator and inlet pipe. I inserted two same size factory restrictors (together) into the solenoid-inlet pipe hose (at the end of it, closest to the inlet hose) and this worked wonderfully.

Jay m A

iTrader: (2)

Wow, 2 gurus in the same thread

Just to update, I ran two 12minute track sessions at Castle Combe and had no noticable problems. The car was down to half a tank at the end (I was using super and Millars octane booster - as always), the car was always above 4000rpm in 3rd, 4th and 5th. The circuit is all right handers bar the 2 chicanes and there were no cut-out moments at all

Inconclusive at the moment so I'll try some more roundabout experiments on a full tank if I get the chance....

Thanks for all your advice people, much appreciated

Justin

John H

Hi Jay M A,
Just thought I'd let you know now we've had some warm weather the over-boost problem has disappeared on my WRX. I think it's because the incoming air is less dense at higher ambient temperatures so if the boost limit is marginal the onset of warm weather 'cures' the problem , well, as long as a british summer lasts !
Regards,
John

Bob Rawle

Jan, you should point out that your car is a MY98 STi Wagon ... totally different set up to the earlier MY's and yes, restrictors are "dangerous" to "play" with. Using the info from the wrong MY car is even more so though. Doing what you suggest on a MY95 will generate huge overboost, with fuel cut, and corresponding issues. Jay m A if you had no trouble round Combe then its definately not fuel cut IMHO (although you would probably need to be below 1/4 tank to be sure). Above 4k the load impedance of the car will be less so its not so likely to happen, also it would have been pretty hot which reduces charge density considerably, especially the older cars with the smaller intercooler.