ScoobyJawa

My MY99 used to have a full magnex decat with a dawes and ITG.

I fitted a Scoobysport BB to replace the Magnex one on Sun and when I was out tonight I got a flat spot in 3/4th gear around 4-5k rpm (not a one off, about 3 times). The car just seemed to stop accelerating and then power off again. It didn't seem to slow down or anything, just stop accelerating beyond the point it already was and then a few hundred rpm later take off again After doing it the third time I tried a rolling start in 2nd, then WOT through the gears and it didn't do it again.......

Is it possible I've not tightened the back box up enough to the mid section and it therefore be blowing, would this cause the problem?

Anyone got any ideas to cause and cure I'd ber very grateful

Cheers
Neil.

ScoobyJawa

John - I really don't think its the Dawes but thought I'd mention its fitted (BTW, you must have about 10 windows open to answer that quick cheers )

Boost looked about normal at around 1.1 bar in 3rd and a bit more in 4th , didn't really notice it drop when the flat spot hit.

Never had a problem with the set up until I changed the BB.... This seems to be why I'm pointing the finger at that
When it went on I hit 1.25 bar several times in fifth (a little spiking). I only hit 1.25 once (not several times) with the Magnex on a very very cold and wet day - perhaps the SS is a bit freer even though they give similar power figures???

Certainly didn't feel right though

ScoobyJawa

LOL - thats no good then, you're fired

I have to say that boost seems pretty unchanged since fitting the SS although like I said 5th on WOT looks to be a bit higher.....

Cheers anyway

Bob Rawle

High boost ...
You have changed the "system" resistance by changing the back box, the Dawes is only a "boost limiter" not a controller and so its a bit slow reacting now if you hit the "sweet spot" for the turbo,play with the bleed opening to sort this out,or adjust the spring pressure in the Dawes to allow it to "crack" earlier, it is a "boost problem" but caused by the exhaust system change. The fact that it used to do it but less bears this out. Its a common problem when cars are decatted running the standard Jecs boost control system as well.
Hesitation ...
You could just be hitting the secondary boost cut which "knocks it back" instead of cutting the fuel/ignition. That is maf derived.

ScoobyJawa

Bob,

Thanks very much for the reply
I understand what you're saying and I certainly agree that the SS seems to have made it a bit freer and thought this could effect the set up.
Take your point that fitting it has just highlighted a minor thing from before but now worse since the new BB, makes perfect sense. Would also seem to indicate too that it could well be a knock back boost cut rather than the all out head into windscreen one as when the revs go higher and the boost naturally drops towards 5-6k then it would be moving down from the cut and hence seem to start pulling again.....? What is the difference between the MAF boost cut and the fuel/ignition cut, and why would I get the first and not the latter (just trying to understand how it works and why )
Does this all make sense or am I talking crap?
I don't really want to play about with the bleed anymore as it is at 1.5mm which seems to work pretty well on the UK MY99+ cars so when you say about adjusting the spring pressure, does this simply mean to turn the Dawes down a little so the boost is not quite so high......?

Thanks again for you input - greatly appreciated

Cheers
NEil.

john banks

Bob I would like to know more about the secondary boost thing please - thanks!

If it is spiking extra bleed would be the way to go- with the Nur Spec it spiked more too. So extra bleed and less spring pressure together will reduce the "gain" on the system but keep the held boost where you want it and reduce the spike a bit and put you back where you were before? 2mm is not so bad and may just do the trick.

You will still gain from the less restrictive exhaust in terms of gas flow, but you will have tamed the boost response if that is the issue.

HELLOM8

I had the same problem, almost like hitting the rev limiter a 4kish. Had the ECU reset and it been fine ever since.
Cheers.
Ian.

mega_stream

If it makes you fell any better I suffered this for the first time on Saturday

I've got a ss downpipe and a HKS Hiper system, so VERY free flowing. Hit about 4k in 3rd and blat car just stopped accelerating for around 1 second then blat back on the power again

Mine also seems to sometimes give a "back-fire" type sound from the exhaust when I change gear on high revs also, maybe as I got an Atmos BOV its this causing it.., seems to be a real kick of power after changing gear, sometimes quite violent, knock you back in the seat type thing.

I run Optimax, no boost gauge or Dawes YET.!! Come next week, I'll have me Dawes and me Defi's

John

ScoobyJawa

Hi John,

That was exactly how it felt, stopped accerating for about 1 sec then power back. It didn't reduce power it just went up, paused at what it had reached for a sec or so, then power back.

I get the odd bang and flame as I change up but not a rush of power like you say, simply more of the same I run Optimax too, perhaps I should try a reset.........

Cheers
Neil.

EMS

John and Neil,

You both hit the boost limit, which activates the "fuel cut"! You have to turn down the boost a little to avoid this.

Exactly as Bob told, a BB can infuence the boost in a mechanicly controled system like the Dawes. (as can different ambient temperatures!)

Mark Verhoeven.

BugEyed

Bob / John

This secondary boost limit on the ECU - is it a fuel / ignition cut, or is it a heap of retard for the ignition? Reason I ask is that I suspect that the MY01 is doing something similar on high boost and is causing an "un-natural" limit to amount of increase in power as you increase boost.

Duncan

PS. I have no facts to support this theory as I don't have the equipment to monitor the ignition setting whilst pulling load. Perhaps someone with access to a rolling road can comment?

dowser

I had peak-boost increase after swapping out my backbox for a less restrictive one, which upset the OE controller (without Dawes ).

I guess the figures you mention above are held? What's the peak doing?

Richard

ScoobyJawa

Figures are held, with the Dawes there is no peak

Looks like I'd better turn the Dawes down a little.

John (Banks ) going on from what you said, do I need to adjust the Dawes and increase the bleed, or just turn the Dawes down a little? If I did adjust the bleed, wouldn't also need to readjust the dawes to put me back where I was before? Is that likely to require the Dawes turning up for more boost, or turning down to reduce? What would you do? Just adjust or adjust and bleed. Once re-set up, how about an ECU reset?

Cheers
Neil.

john banks

The I-club guys are always going on about the amount of retard they get over 15 PSI on OBD II analysers over 15PSI.

You could try turning the Dawes down, if not add more bleed and turn it down some more.

I have not encountered a MAF mediated boost cut on MY00 PPP, only get MAP sensor doing it over 19 PSI if I am interpreting things correctly.

With OEM setup the solenoid will pull back the duty cycle if the boost goes too high too quickly - hence the reason I got rid of it - slowing me down too much!

[Edited by john banks - 2/13/2002 11:31:53 AM]

ScoobyJawa

Thanks John, I'll give just turning it down a bash and see how I get on Scott W has the full SS system running the same bleed and his is ok so I think I should be ok if I just turn it down a bit

Cheers!

mega_stream

But I've not got my Dawes yet, so how can I be running too much boost and turn it down


Whats making me over-boost? The BOV???

John

john banks

Restrictor orifice can be enlarged on MY99/00 to reduce peak boost - see threads in the dawes faq.

ScoobyJawa

John (mega )

Bob said above that this is also a common problem on standard cars with a decat so that could be why you get it, as John (banks this is getting confusing ) said, you might need to play with restrictor sizes to slightly lower the boost.

Cheers!!

The_Gza

Neil,

I've experienced exactly the same problem you describe in my MY00 with Scorpion d/p, Janspeed centre and Magnex b/b and ITG.

Does opinion therefore favour the standard ECU being unable to cope with the messages it is receiving due to the exhaust and filter changes (i.e. you've changed the 'system resistance' as Bob put it), and pegging back the cars performance - by whatever means?

The sooner I get rid of that AE802 green ECU the better



[Edited by The_Gza - 2/14/2002 9:12:06 AM]

ScoobyJawa

Hi Gza

As a note mines running a black 800 ecu and still doing it so its got to be sorted somewhere else I would imaginge, like John said, probably with restrictors although for me I can just turn the Dawes down a bit

Cheers!

FOZ STiV5

Hi all,

I can confirm that when I switched a standard system on a STiV the boost response bas unbelievable and so to was the boost figure....off the gauge.... I tried a less sensitive gauge and got 18psi every throttle. I am not sure what standard boost is on my car as I only just got ?? anyone know.

Anyway I have put the cat DP back on but still the boost is 18psi. Anyone tell me what the dawes is??? and a link..sorry for being a newbie.

Cheers

john banks

You don't want to touch the Dawes if you have an STi. End of story.

ScoobyJawa

Ok, in the pouring rain and cold last night I re-adjusted the Dawes down a little bit. I then went out for a good run and was unable to hit the flat spot again, so it looks like that has cured it

As a note, after turning down the Dawes my Defi now reads a peak at 1.2, holds 1.0 in 2nd 3rd, 1.05 in 4th and 1.1 in 5th. I think also that the gauge is slightly under-reading.

Cheers for all the replies
Neil.

Scott.T

iTrader: (2)

This sounds like the exact problem I have on my MY94.
I've been trying to cure this for about 10 months and have currently changed/borrowed everything except the Throttle Postiton switch and Knock Sensor. And had a session at PE and Barratts.

How come I am experienceing this same problem which can be provoked in 1st and 2nd gear between 4,000 and 5,000 rpm when giving it WOT, even with the car in standard form running approx 11/12psi or higher boost of say 14/15psi.

Would it be worth adjusting the size of the brass restrictor i.e remove it and fit my bleed valve in that cicuit so that I can adjust the bleed off/rise time.

Gonna try re-grounding the ECU at the weekend.

john banks

Did you notice what the boost was doing? Seems an unlikely cause though if you have the Dawes? Dodgy fuel? Going round a corner on a low tank? Could it be unrelated to the backbox?

[Edited by john banks - 2/12/2002 10:18:08 PM]

john banks

A backbox can make a difference to your boost - mine went from 18.5 to 20 PSI after a few miles on a Blitz Nur Spec which was big enough to swallow my PPP backbox and a heck of a lot less restrictive obviously. But it doesn't really sound like a boost problem so I can't help you any more I only know about boost

[Edited by john banks - 2/12/2002 10:27:47 PM]