1.3-1.5 bar boost - aby - boost leak???

[S2Ian]

i have a 95 aby coupe it has homefry but apart from that its standard engine, it seems there is something wrong, in 6th if i put my foot down i used to get something similar to 1.7 bar of boost, now im getting 1.3 - 1.5 bar of boost, is this the overboost protection kicking in because i may have a leak? have checked all the hoses in the engine bay, all appear to be on fine, have checked vacume hose to difflock & hose from boost guage.

only thing is, it went inot garage to get lowered and it seems to have been doing it ever since, could the garage have knocked a hose or something round the suspension legs?

have no idea what it is... HELP

[Bram]

How did you get 1,7 bar??? Are you still running the standard S2 turbo (k24)?
Normally a ABY should do 1,4 bar in overboost.

[kwlw]

only thing is, it went inot garage to get lowered and it seems to have been doing it ever since, could the garage have knocked a hose or something round the suspension legs?

If you are talking about internal boost gauge readings? With homefries it should show something about 2.3-2.4 bar if engine is healthy. So 1.3-1.5 bar means "safe mode" of the ECU.

You are right - first check boost hoses, next if boost not right - read ECU codes. If nothing there, then use Search for "no boost","low boost","MFTS boost","N75 boost", "faulty bypass valve","knock sensor issue" and read, read, read.

Sau

[S2Ian]

cheers will check that out, yeah was talking about the internal boost guage. wouldnt of thought id be doing 2.4 bar at any time, that would mean running like 35-38 psi...

[S2Ian]

if i had a fault with the lambda sensor would it have this affect? the sensor was showing faults at the mot... but they cleared teh fault codes and it got a lot better boosting to 1.7 bar but it appears to have come back....

[UrS4boy]

cheers will check that out, yeah was talking about the internal boost guage. wouldnt of thought id be doing 2.4 bar at any time, that would mean running like 35-38 psi...

On thing that often needs to be cleared up when people speak of "boost" is whether it is absolute or relative pressure. For example, the internal (digital) boost gauge on, say a 92 spec UrS4, is absolute pressure (where zero is a complete vacuum). These cars typically boosted to about 2.1 Bar (1 Bar = 14.5 psi) or 30.45 psi absolute. This is about 15.75 psi (relative) when you remove atmospheric pressure (about 1.01 Bar or about 14.7 psi). With stock overboost, you might get another psi or 2 psi, but that's it with a stock ECU and K24.

The typical stock AAN (and I presume ABY) was gate spring provides about 6 psi of mechanical boost limit. This is about 0.4 Bar. So, with an internal digital gauge reading of 1.5 Bar, all you are getting is mechanical boost limit. This typically happens when the boost signal hose to the ECU is disconnected and it isn't being told that there is any boost happening. The other way this could happen would be if the N75 waste gate frequency valve (WGFV) was disconnected. In that case the ECU would be signalling the WGFV like mad but the WGFV wouldn't be listening. Hence, back to the waste gate spring mechancal boost limit.

Check your WGFV connections (both mechanical and electrical).

Dave F.

[S2Ian]

checked all the connections earlier, then took it out for a drive, it was all over the place, when i accelerated hard the guage would rise to about 1.3 bar, then fall back to about 1, if i was in a higher gear like 5 or 6 it would stay around 1.4-1.5 bar, im feeling a loss of torque and the boost guage is all over the place... so i pulled up, checked under the bonnet, i seem to be able to hear the re-circ valve a lot more at the mo, like its putting a lot more air back into the system for some reason...

[A8_Dan]

On my S4 i had an EGT sensor fail on one bank, this caused no loss of boost. However, a few months later my boost dropped off to about half! Sometimes it fully boosted most of the time it didnt. Chacked the car and my EGT on bank 2 had failed this time. Changed it and car was fully boosting every time. So could possibly be the cause of lack of boost. But either way, If the Lambda sensor has failed then it needs to be changed sooner rather than later, as on the S4's it can lead to the early death of the Maf!

Dan

[S2Ian]

now i feel like a noob, what does egt stand for???

[UrS4boy]

now i feel like a noob, what does egt stand for???

Exhaust Gas Temperature. However, on the UrS4 (AAN) and I presume the S2 ABY, there is NO EGT sensor. However there is an oxygen sensor. Maybe this is what A8_Dan was thinking of (???).

Dave F.

[Dan_s2_coupe]

I think he means a newer s4 V6 bi-turbo

[Jonas_R]

There is still something I dont understand. How can you be getting 1.7 bar boost on Homefries? If we are talking relative pressure it should be around 1.4-1.5 bar boost max on stock K24. If you are talking absolute pressure should be getting 2.4-2.5 bar boost max. So if you are refering to 1.7 bar absolute, then something was wrong from the start. If you had 1.7 bar relative pressure, then I would say something was wrong with your boost gauge.

So which one is it, absolute or relative?

/Jonas R.

[UrS4boy]

So which one is it, absolute or relative?

/Jonas R.

Exactly my point. We need to be clear about absolute or relative boost (in either Bar or psi) when we talk about boost "problems".

Dave F.

[HPmuirt]

1.3 - 1.5 Bar relative boost for a homefries sounds bang on to me for an ABY.

My ABY boosted at 1.15 on overboost, which rose slightly when I added an RS2 airbox plus MAF and a VDO boost gauge to read it more accurately. When running on a homefries the same setup gave me 1.3 Bar standard and 1.5 Bar on overboost.

When you say that your boost varies a lot, you have to remember that a gently opened throttle will never initiate overboost and you only get full overboost in the upper gears and when you request full bost by stamping on the pedal below 3000rpm (ish). Therefore, depending on your revs before you accelerate, your gear and the speed you hit the throttle, you should see either 1.3 Bar (standard full boost) or 1.5 Bar (on overboost).

1.7 is reportedly just not possible on the K24 turbo (homefried or not).

You would have to work hard to knock something when doing a suspension change and I have never heard of 'overboost protection'. I would say the car is doing what it should

Cheers n

Si

[Jamo]

checked all the connections earlier, then took it out for a drive, it was all over the place, when i accelerated hard the guage would rise to about 1.3 bar, then fall back to about 1, if i was in a higher gear like 5 or 6 it would stay around 1.4-1.5 bar, im feeling a loss of torque and the boost guage is all over the place... so i pulled up, checked under the bonnet, i seem to be able to hear the re-circ valve a lot more at the mo, like its putting a lot more air back into the system for some reason...

That is correct, I noted the boost levels of your car here http://www.s2forum.com/forum/showthread.php?t=10806

It boost higher then drops because of the overboost function of the ecu of the ABY http://s2central.net/motronic_03.html

It will never hold maximum boost for more than 15 seconds.

no way should it be boosting to 1.7 bar. It only has a 2.5 bar MAP sensor in the ECU which means it can only control boost to 1.5 bar max.