another s3 boost problem

[Mpathe]

ive got a 99 s3 that was remapped at awesome gti last yr but now ive got vag com ive noticed that its not boosting to 2500mbar as expected neither is it being requested by the ecu. ive replaced all the vaccum pipes, checked boost pipes, renewed the maf, renewed the n75, checked the 1 way valve in the oil breather pipe.
and still no change,
its requesting 2100mbar and prduces 2000mbar
the maf readings are abit low aswel about 160
lamba readings sit at about 0.8 when on boost

any help would be much appriciated as im running out of ideas now thanks mike

 

[s3dave]

worn actuater?

 

[Prawn]

160g/s suggests only around 200bhp or so, and 0.8 lamda is very rich indeed. I wouldn't think it's a boost leak, as cars with boost leaks tend to still give high MAF readings, as it's being sucked in, then lost after the MAF.

ANy fault codes?

 

[Mpathe]

worn actuater?

that reminded me i thought of this and i dissconnected the vaccum pipe going to the actuator and i got 2480mbar actual boost pressure but didnt know if it ment the actuator was ok or not.
no faults code neither

 

[OllieH]

With the vac pipe removed from the actuator you should not be getting 2480mbar as the wastegate in the turbo should now be opening at a base setting, which I think is about 7 psi?

 

[Mpathe]

i pretty sure its the other way round ie waste gate fully shut off and when the correct pressure in vaccum pipe is reached then it opens but might be wrong

 

[<tuffty/>]

With the vac pipe removed from the actuator you should not be getting 2480mbar as the wastegate in the turbo should now be opening at a base setting, which I think is about 7 psi?

i pretty sure its the other way round ie waste gate fully shut off and when the correct pressure in vacuum pipe is reached then it opens but might be wrong

Soz Ollie, Mpathe is correct, if he did indeed remove the pipe off the back of the actuator it would stay shut... disconnecting the N75 electrically will allow the actuator to operate at its preset pressure... 0.5bar in this case...

I would drive about producing that kind of boost if I were you though... apart from potentially running lean and melting the engine, the boost spike alone could bend the rods... Remember that the MAP sensor will only read up to 1.55bar and the reading in vagcom doesn't take atmospheric pressure (typical around 1000 mb) so take 1000 off what VAGCOM tells you... if you get a reading of 2540 for any length of time peak boost is quite probably more than 1.5bar and you can wreck your engine....normally if the ECU detects that much deviation from requested to actual it will switch off the N75 reverting back to actuator pressure and go into limp mode... this won't happen while the actuator pipe id removed as there is nothing to control...

Be wary...

<tuffty/>

 

[Mpathe]

i only dissconnected it for 1 boot to see if it boosted higher than what im getting, tuffy do you think it rules out a weak actuator or still could be possibility

 

[OllieH]

Soz Ollie, Mpathe is correct, if he did indeed remove the pipe off the back of the actuator it would stay shut... disconnecting the N75 electrically will allow the actuator to operate at its preset pressure... 0.5bar in this case...<tuffty/>

I stand corrected. I was getting mixed up with the electrical disconnection of the N75. :icon_thumright:

 

[<tuffty/>]

If vagcom says its requesting 1.1bar and actual is not far off then it isn't the actuator...

Typically a stage 1 map will spike to 1.4bar then hold about 1.1/1.2bar. No stage one map I know of requests 1.5bar.

160g/s is low... stage 1 remap should be around 200g/s on an S3.

How did you log the run? Which blocks and what gear?

<tuffty/>

 

[Mpathe]

i did 115 031 002 using vag com and have done them in 3rd and 4th gears from 2000 to 6000 revs

 

[Effect]

I would be interested to know what the answer to this is.
As mine is requesting 1.4 and actual is 1.2bar, MAF reading is also low on mine at 182 g/s, so it sounds to me like we have a similar problem.