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Hi rtl5009,
just come across this thread as I have the same P0491 and P0492 error codes on my 05 997CS. Did you replace the pump and valve? Did you identify what the problem was? Could you replace the pump and valve without dropping the engine?
I’ve done some research on the SAI system and the rusted up change over valve you picture above is nothing to do with the SAI system, it’s for the resonance valve in the rear cross pipe between the 2 intake manifolds. The Porsche part diagram is very confusing in this regard. I think it’s a mistake carried over from the 996 which did have a change over valve because the check valve was vacuum operated. On the 997 the check valve is pressure operated. When the pump is on, it just pushes the valve open.
It actually was the valve- it was locked up and not opening 100% when the pump kicked on as the pressure from the pump could not overcome the resistance. You most definitely have to drop the motor to get to the pump as you have to removed the drivers side intake manifold and I am not sure how you will get the back IM bolt without lowering it. You are right on the vacuum, there is not vacuum that goes to the SAI system. Its a pump, hose, and valve- the pump overcomes the valve and the sai air flows through. My pump was perfect. I just replaced the valve and gasket.
I recommend buying a used pump system off of eBay and brand new gaskets for the valve and frame, that way you can have any and all parts you could need when you tear it apart. Make sure when you get the "new" system to test it and remove the cover and look at the blades, you can run it off of any 12v source, a car battery works great. The first one I got off of ebay had a broken fan but the seller was quick to make it right.
Thanks TopKatz and rtl5009 I’m also hopeful my problem is just the pressure operated non-return valve. I can hear the pump operating for about a minute and a half on start-up. Do you know if just the valve can be removed with the engine in situ? I took the photo below when I replaced the starter. I had to remove the alternator. The valve is clearly seen and is held by 2 screws which fit from the underside. I’ll have a go at removing that first. If I do need to drop the engine, I have the tools for doing it as I rebuilt the engine last year due to bore scoring.
Thanks TopKatz and rtl5009 I’m also hopeful my problem is just the pressure operated non-return valve. I can hear the pump operating for about a minute and a half on start-up. Do you know if just the valve can be removed with the engine in situ? I took the photo below when I replaced the starter. I had to remove the alternator. The valve is clearly seen and is held by 2 screws which fit from the underside. I’ll have a go at removing that first. If I do need to drop the engine, I have the tools for doing it as I rebuilt the engine last year due to bore scoring.
you MIGHT be able to get the valve itself using a 1/4" bit with a wrench but you will not be able to remove the pump without removing the intake. It’s going to be super tight to even get the valve. And you will want to remove the whole thing to test whats exactly wrong. Mine actually went bad after an R&R of the motor too, I'd image carbon gets loosing during all the fumbling and locks its up. Did you rebuild the motor yourself?
Yes I rebuilt the engine myself once Hartech had re-manufactured both blocks with their closed deck nikasil cylinder liners. I’m an aeroengine designer by profession and have always been intrigued by the Porsche flat six engine, so took the opportunity to buy a cheap 997 with a bore scored engine. I always intended to sell it on after I’d finished it but I’ve enjoyed driving it so much I’ll be keeping it.
Yes I rebuilt the engine myself once Hartech had re-manufactured both blocks with their closed deck nikasil cylinder liners. I’m an aeroengine designer by profession and have always been intrigued by the Porsche flat six engine, so took the opportunity to buy a cheap 997 with a bore scored engine. I always intended to sell it on after I’d finished it but I’ve enjoyed driving it so much I’ll be keeping it.
Got any pictures? rtl5009@gmail.com- once my fidelity warranty is up I am probably going to build mine to a 4.0L with LN Nickies- Built alot of audi motors in the past, never a flat motor.
Yes loads of pictures, here’s a few along with a movie of the first turn of the key if it’s uploaded.
It took me 9 months from start to finish but I was only doing it in some of my spare time. A great sense of achievement when it’s all finished and running!
It is possible to remove the SAI non-return valve without lowering the engine. It is quite an easy job. I removed the air box, alternator and knock sensor and then the access was sufficient to get a 30 torx tool into the screw heads. I then tuned it with mole grips as shown below.
Sure enough the problem was this valve, totally jammed and not opening. I used my Durametric to activate the pump and it works fine creating a powerful flow of air down the pipe without the valve connected. So just got to order a new valve and it’ll be job done.
03-27-2020, 09:22 AM
