Help sorting my underboosting S2?

[gunman]

In higher gears the cars wont reach 1.4.... they should only hit 1.4 in 1 - 4 gear so I believe????? Or is it the other way round????

That was my understanding of it too. I thought max boost would be had in 2nd and 3rd.

[Christophski]

Yeh, Does your boost guage sit at 0 when the car is turned off as mine sits very slightly under 0 hence when on full boost it reads just under the points it should reach....

[montez]

Also what vacuum are you getting on you boost gauge when you are idling and on over run?

[gunman]

Similar on the boost gauge, very slightly under 0 when ignition off, at idle it shows -0.5 (the lowest possible reading as there's a stop here). Gauge is a VDO one.

Cheers

[gunman]

Something else I forgot to mention, theres sometimes a very slight bit of hunting at tickover, esp when you rev it up and lift off. It takes a few seconds for the idle revs to stabilise. This also led me to think it was a VAC\boost leak. One of the guys I work with's Dad runs a garage and he says he has a smoke test kit for checking for leaks. I may give that a go and see what he finds as I was getting nowhere myself.

Cheers

[andyg plym]

you should be achieving max boost in 4,5 and 6 gears

have you checked all vaccum hoses even the one hidden away on the bottom of the turbo? the one that connects to the bottom of the n75,mine went recently and was exaxtly the same symptoms

[dodger]

I just had a simular problem on my s6 c4. Most likely a leaky hose somewhere. Check if you have a leak in the Turbo Bypass Valve. Check how much boost you get when unplugging the N75, if you get less than 0,4, your wg spring may be to soft. Check the small pressure hose that goes from the intake to the ECU. Also a clogged cat(exhaust backpressure) can be the reason for low boost. More troubleshooting can be found here http://www.sjmautotechnik.com/troubl.../20vboost.html.

[Christophski]

Cheers Andy, knew it was one way or the other. So yeh in the lower gears you should only hit around 1.2bar... If your guage sits below 0 when turned off then You may not have a big boost leak. Its more noticeable in the higher gears though. If you are int he higher gears with boost on full (the lowered level you seem to be getting) if you lift off the throttle then put it straight back down does the boost level go up to 1.4bar then?

[gunman]

Cheers Andy, knew it was one way or the other. So yeh in the lower gears you should only hit around 1.2bar... If your guage sits below 0 when turned off then You may not have a big boost leak. Its more noticeable in the higher gears though. If you are int he higher gears with boost on full (the lowered level you seem to be getting) if you lift off the throttle then put it straight back down does the boost level go up to 1.4bar then?

I doubt it but it's a test for the way home.

Cheers

[Christophski]

Mine does it sometimes and if I let off then hammer it straight away the boost goes back up higher.

[prj]

My S6 always hit 1.5+ in 2nd on my tune.

[Christophski]

Seems like one day i will be after a PRJ tune then so I can hit that in my S2!

[gunman]

Just an update on this.

I have take off the boost pipes this evening and checked them all, I have replaced all the vacuum hoses in the engine bay and taken the car for a run. Still hit 1.1bar max.

Disconnected the N75 and got 0.4bar boost. Reconnected it and disconnected the MFTS, still got 1.1bar max.

Looked it over again and found that the short rubber hose between intake pipe and inlet manifold had a loose hose clip (3-4 turns out). Thought that must be it and took it for a run, 1.1bar max.

Thought I'd check out the diff lock hose, looked under the back seat and found the small green plastic vacuum hose going to a module under the back seat, as it was dark and I wasnt for getting under the car I removed it (heard a hiss when I did) and blocked it off.

I took the car for a run, you guessed it ...1.1bar max...at first, but one one of my more spirited runs it actually did hit 1.4bar, albeit for a fraction of a second, then I heard a whistle and it dropped straight back to 1.1 bar. I couldn't get it to do it again after that but it did hold at 1.2bar a couple of times.

No idea what to do next.

[prj]

Check dump valve.

Also, when you boost leak tested it, how long did it hold 0.5 bar?

[gunman]

I've the car booked in to have a boost leak\smoke test done on Thursday eve, here's hoping we find out where my boost is going.