Question about exhaust pressure in a TDI between the engine and the turbo

[03TDICommuter]

Does anyone know - is the exhaust pressure in the runner/manifold between the turbo and cylinder head generally higher than the pressure on the intake side?
I'm guessing yes otherwise the EGR wouldn't work, but can anyone confirm?

The question popped up in my head while trying to determine if I have a EGR cooler leak or a headgasket leak (guessing headgasket due to the 'one way valve' nature of the failure.

 

[MukGyver]

Does anyone know - is the exhaust pressure in the runner/manifold between the turbo and cylinder head generally higher than the pressure on the intake side?
I'm guessing yes otherwise the EGR wouldn't work, but can anyone confirm?

The question popped up in my head while trying to determine if I have a EGR cooler leak or a headgasket leak (guessing headgasket due to the 'one way valve' nature of the failure.

The egr only opens at lower rpms so the intake pressure is low then because of low turbo speed. Therefore when the egr valve is open the intake pressure is lower than the exhaust pressure.

 

[MukGyver]

Hope that helps 03tdi. Why do you think your head gasket went kapoot? What did you mean by the one way valve nature of it?

 

[03TDICommuter]

Hope that helps 03tdi. Why do you think your head gasket went kapoot? What did you mean by the one way valve nature of it?

I've got foam in the coolant ball and it smells funny. It's been using a little coolant and I've always got some air in the upper radiator hose. I put an ultraguage on it to see if it's overheating (it's not), but I'm see some overboost (~22-23 psi) sometimes. This is with a Malone stage 1. Now I know why my original clutch was slipping at low RPMS in 4th and 5th. Guessing this overboost also made my old headgasket start to fail. At idle I'm not seeing any foam, only when driving with some boost.

Every time I've checked coolant pressure the next morning, it's not pressurized. I'm not seeing smoke out the tailpipe and it's cranking fine so I'm wondering where the pressure is bleeding off to. I don't know if the EGR cooler can cause foam in the coolant, and the exhaust pressure would need to exceed the coolant pressure to do it, hence my question.

One way valve nature, is that it's pressurizing the cooling system, not to the level of blowing out the coolant, but it's also not depressurizing fast and pumping coolant into the oil or cylinders.

When I do the headgasket, I'll also take the turbo apart and clean the control ring/vanes. Also the intake runners for buildup, and finally replace all the vacuum lines and N75 valve to see if that solves the overboost.

 

[MukGyver]

Sounds like you're reading all the symptoms correctly to me. my stock bv39 runs at 22 psi for short durations which seems a little high since I have no tune. So I wouldn't think the pressures you mentioned would lift the head. unless maybe prolonged stretches running that high? I think the last thing you mentioned to service turbo and n75 vacuum is a great idea to do. Loss of pressure in the morning I would think is pretty normal for systems cooling overnight.