10-16-2012, 07:22 PM #1
- Join Date
- Feb 2008
MSX150 POP OFF VALVE (BLOW OFF) Testing
Is there a post anywhere on testing the pop off valve on the MSX150. This is the black plastic (BOSCH) diverter valve to the left of the intake manifold.
I found a simple test online to verify that the diaphragm is intact. I tested my valve and it passed this test.
I then connected the inlet to a pressure regulator to see at what pressure the air would leak throught the valve. My valve started to leak air at less than 5 psi. At 14psi the air was flowing unrestricted past the valve face. I would have thought this valve would hold pressure to at least the normal boost pressure at WOT (14.4psi). Is this leaking valve not causing a boost leak.
for reference valve looks like one in this link http://www.ebay.com/itm/Porsche-911-...e7b4ee&vxp=mtr
10-17-2012, 09:52 AM #2
Your on the right tract with your testing... but did you put that same pressure into the diaphragm small hose at the same time? If not, the diaphragm will lift off it's seat and leak.
It takes equal boost pressure on the "backside" of the diaphragm to help keep it sealed while the intake tract is under boost. The diaphragm hose gets it's boost source from the intake manifold. When the whole intake tract including the intake manifold (throttle open) is under boost... that diaphragm line will also have the same boost pressure. Only once the throttle is closed does that intake manifold and that diaphragm line both go into instant vacuum (while the intake tract up to the throttle is still under boost). This vacuum on the diaphragm line is what instantly lifts the BOV diaphragm and vents that stacking boost in the intake tract... so it doesn't create a pressure wave and surge back to the turbo and stall out the spinning turbo (often heard as a turbo flutter).
Give that a try and see if your BOV doesn't hold pressure up to at least 15psi.
10-18-2012, 05:02 AM #3
- Join Date
- Feb 2008
ripcuda. Thank you for reply. Will try this later today. I think if I test correctly I will find it is working fine.
Think i may have found my problem. Rubber joint under throttle body had blown off, leaking boost.
Funny thing is now it is back on and running on the hose it no longer runs away if I do not have it in reverse. It returns to 1500rpm idle everytime.
Hoping to water test later today.
10-18-2012, 10:17 AM #4
Good catch! Those rubber throttle body -to- intake seals are a good place to check for leaking boost. And if they leak boost out, there's a good chance they also leak air in when the intake manifold is under vacuum like at idle. This would be like opening the throttle a tad and the ECU not being aware of it.
Still warm enough for riding in your locale? I'm jealous! Our lake is getting frigid up here near the 48th parallel.
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