Ahsai

I'm in the process of replacing my AOS and the starter cable so I have the left intake manifold off the engine ('03 C2 coupe manual transmission). While I'm in there, I decided to refresh my vacuum system and replace all the vacuum lines, the rubber Y's and elbows, the vacuum reservoir, and the two changeover valves. All that for only $130. The stock vacuum line is available from Porsche for a few bucks per meter and you need about 1,200 mm. You can also replace them with your favorite vacuum hoses. I stay with stock lines since they hold up surprisingly well and they are light and less bulky.
Stock vacuum hose line P/n 00004320501 (1m)

I just want to document the info here hopefully helping the next guy.



My stock vacuum lines are still in very good shape as far as I can tell but the problems are all the "Y" and elbows. They are not sealing the best. Also, the vacuum reservoir is leaking slowly while tested with a hand vacuum pump. I also tested the changeover valves and they are all good.

The system is very simple. The vacuum is supplied to the one-way check valve from the intake plenum then it branches off to the vacuum reservoir and changeover valve #1, which powers the intake resonance actuator when electrical power is supplied.

The vacuum reservoir then supplies vacuum to changeover valve #2, which powers the SAI one-way check valve that opens whenever the SAI pump is running.

To check the system quickly, you can use connect a hand vacuum pump to the black/white valve and create vacuum. Then you power each changeover valve and you should hear the resonator flap rotates and the SAI valve moves as well.

To check whether the WHOLE system holds vacuum, remove the black/white valve and connect the pump there and start pumping. Vacuum level should stay once you reach some vacuum level and stop pumping.

Nedster

Excellent info, especially since i was contemplating rigging up a home made smoke machine to do a vacuum test on my car.

Ahsai

I built one a long time ago but never have a chance to use it yet
See my design here http://www.garagejournal.com/forum/s...&postcount=140

Paul Waterloo

Thanks for the info!

Nedster

That's a lot more sophisticated than what i had in mind, looks good! I was gonna just use the old Home Depot 5gallon pale with a lit cigar in it and a compressor

Ahsai

Or try this haha

Nedster

Yea, that would be the "manual" mode on my contraption (now i have to add a switch)

Ahsai

Leak found at bottom of the vacuum reservoir at 6 PSIG.

DK570

Great write up Ahsai. I've been struggling with codes p0491 & p0492. Knowing that you replaced all that for about $130, I may do the same. The dealer has tried, but been unable to make the codes go away. They replaced a hose they thought was cracked, which made the whirring noise I heard at 80+ mph go away, but the codes still came back.

Ahsai

Yea, I got all the parts from Sunset www.porschepartshub.com

Do you hear your SAI pump running at all? Your codes indicate that both banks dont see fresh air. Once you remove the parts I show here, you can attach a vacuum pump directly to the SAI metal one-way check valve on top of the engine, apply power to the changeover valve and blow in the hose that's connected to the SAI pump (after disconnectimg it from the SAI pump end). If you can blow through, the SAI valve is working and the fault is likely at the rest of the system where you can test each part individually.

ssmyth

Hi,

I was also getting those codes and found some leaks and a bad solenoid using a hand pump - see rennlist.com/forums/996.../802749-quest-of-the-vacuum-leak.html

I cleared the codes but they soon came back. When installing some Fabspeed cat bypass pipes, I found that one of my cats was loose and was hitting the O2 sensor.

For me, I think this was causing these codes. The codes are gone but I have a new one due to the cat bypass.

Steve

Ahsai

Yes, the SAI changeover valve is definitely a suspect. Btw, there's an updated version of those two changeover valves - p/n 7PP906270 (non typical Porsche p/n).

DK570

Yes, the pump definitely runs. Dealer receipt basically says (paraphrased) checked SAI pump, checked checked SAI valve, checked RKAT values, pressurized system and checked for leaks, replaced hose.

dporto

"Dealer receipt basically says (paraphrased) checked SAI pump, checked checked SAI valve, checked RKAT values, pressurized system and checked for leaks, replaced hose."

That's shorthand for "We didn't do **** except replace a cheap vacuum hose, but we charged you a crazy price for it, and also for the time we spent not finding any problems - but the book said it should take 3 hrs. @ $150/hr. so..."

dallison28

I have just replaced a couple of the lines. If the lines are longer than specified, would that contribute to a rougher rev from 1-2k rpm?