Overboost cut out

[94S2Sedan]

Cheers,
My car has been running quite odd recently. I have noticed that its overboosting to much, I have a stage 1 Ultimot chip (i know its ****) And the over boost is set to max out at 1.7 Kilos, But lately it has been overboosting around 2Kilos shown on the Boost gauge and i can feel the ECU having to intervene to get the pressure down to 1.7 Kilos. I can tell that the car has not been running as strong as it did before, Dose anyone know what this issue might be????

[willg54]

any fault codes?

boost leak between n75 and wastegate?

[94S2Sedan]

any fault codes?

boost leak between n75 and wastegate?

Last time i scanned the car it said maximum RPM surpassed, Transmission Speed sensor no signal,and i think it said maximum boost pressure surpassed.....But that dosent tell me more than i already knew...

[UrS4boy]

Cheers, My car has been running quite odd recently. I have noticed that its overboosting to much, I have a stage 1 Ultimot chip (i know its ****) And the over boost is set to max out at 1.7 Kilos, But lately it has been overboosting around 2Kilos shown on the Boost gauge and i can feel the ECU having to intervene to get the pressure down to 1.7 Kilos. I can tell that the car has not been running as strong as it did before, Dose anyone know what this issue might be????

Kilos is a measure of mass. Pressure is mass/unit area so I assume that you are talking kilograms per square centimeter where 1 kg/cm^2 = 0.981 Bars = 14.2 pounds per square inch (psi). So 1.7 kg/cm^2 = 1.67 Bar = 24.2 psi. Which is nice relative pressure for boost.

You don't say what Manifold Absolute Pressure (MAP) sensor you are using with the Ultimot chips. Presumably, Stage 1 = the stock 250 kPa (2.5 Bar absolute pressure = about 1.48 Bar relative (21.5 psi or 1.51 kg/cm^2 relative boost pressure)). On that basis, even the 1.7 kg/cm^2 is over spec. Perhaps you have a 300 kPa MAP sensor which would allow up to 28.8 psi or 2.02 kg/cm^2 relative boost pressure.

In any event, you need to re-check the hoses to the wastegate frequency valve.

MAP info = http://forums.quattroworld.com/s4s6/msgs/20417.phtml
WGFV info = http://forums.quattroworld.com/s4s6/msgs/20987.phtml

[newsh]

Yes, check WGFV (N75) for cracks, leaks and sticking (try spraying some WD40 in it)

Check the hoses to and from the WGFV, particularly the hose from face of turbo to valve and from valve to wastegate.

Plug a piece of vac hose onto the nipple on the top chamber of the wastegate and suck, it should hold vacuum, if not your WG diaphragm has a split.

Pull the vac hose off the IM which goes to the DV and suck, should hold vacuum.

[prj]

Wastegate diaphragm - check that first, then N75 and the rest.

[94S2Sedan]

Thanks guys, I have been really busy lately haven't had time to check the car out... I'm going to look for the problem tomorrow, I'll keep you guys posted.