andydoody

Hi Beepbeep. My apologies, I thought I was replying to a post by Dave. Thanks for the suggestion.

andydoody

Got the car back from the exhaust shop where they sealed up two leaks; one leak was located just at the junction of the downpipe and the other at the connection of the muffler. It looks like the exhaust leaks were a good contributor to the hight fuel pressure. The fuel pressure dropped from 69 PSI to about 61.5 PSI at idle.

The exhaust leak must also have an effect on vacuum because it's now 16 in. Hg with a cold engine at idle and only headlights as load. That's an improvement from 20 in. Hg. Strangely it stays at 16 in. even at operating temperature. With an aircon load, and warm engine at idle the gauge fluctuates between 11 - 12 in. Hg. The needle fluctuates as the aircon compressor switches on and off.

Check engine light still comes on and goes away with a blip of the throttle or while driving briskly. The engine is still running rich but the smoke and richness in the exhaust has diminished. One can really tell that the engine is breathing a lot better. I haven't done any WOT runs to check if top end boost has come back so nothing to report there.

So far the rich running looks to have a direct connection to the fuel pressure. I'm in process of building a DIY boost leak tester. Hopefully this tool will give me a definitive answer to the presence or absence of leaks. I've only found notes on leak testing the turbo to intake portion of the hoses. Appreciate any info on how to perform other leaks tests including the vacuum hoses.

UrS4boy

What? Did you even click on my link to boost testing procedures? Many options there and, to cover all the bases at once, this comment, just above the testing options table:

"Here is a table that outlines the various boost testing options based on the above diagrams. Note: The table was set up to isolate certain components. Many people, most notably prj (dmitri) on the S2Forum and Marc S. (at EFI Express) have suggested that the simplest method of boost leak testing that captures all the possibilities in one go is to place the pressure bung in "A1" in the diagram and disconnect the hose from the cam cover to "A3" and plug "A3", leaving the rest alone. This falls some where between test Option 1 and Option 3."

Try again: https://www.audiworld.com/forums/sho...php?p=24413028

andydoody

Got it! Thanks Dave

andydoody

Hi Dave. Finally got the time to do a proper boost leak test following the instructions on your post. Heard a loud hiss of air and found the leak with a spray bottle of soap. The N80 valve was leaking from the area of the electrical connector. It's a big enough leak to go from 10 PSI to 0 PSI in about ten seconds. Could this be causing the high fuel pressure, rich running, and low boost?

UrS4boy

Well it certainly would cause a boost air leak, i.e. air that has been metered by the Mass Air Flow (MAF) sensor has gone missing. This results in running rich because that air was expected at the cylinders by the ECU and the ECU had set the fuel injector duty cycle based on that expectation. I don't think it explains the high fuel pressure.

More reading = http://www.motor.com/magazine/pdfs/102007_04.pdf

More N80 info: HERE

andydoody

Thanks again for the info Dave. I'm trying to get my hands on a new N80 valve (034133517 or Bosch 0280142155) but the only one available is a Bosch 0280142300. The two parts are different in color; original is blue and Bosch is black; also different is the direction of the arrow on top of the valve.

Would you know if the Bosch 0280142300 can be used on our cars?

UrS4boy

Seems like it is just black because it is the universal replacement evaporative emissions canister valve. Cheap enough:
http://www.ebay.com/ctg/Bosch-028014...alve-/74467256

I presume you'd have to match the flow arrows even if it means turning the valve around relative to the Audi blue one.

andydoody

Hi Dave. Just to confirm, the 280142300 part can be used in our cars? Won't the fuel vapor flow be somewhat restricted if the part were turned around to match the direction of the arrow on the original valve? My apologies for seeking clarification; the same part over here is the equivalent of $130. Thanks again.

UrS4boy

If the OE flow arrow points towards the intake manifold, the aftermarket part arrow needs to point in the same direction. If you are hesitant in trying the aftermarket part, then go with the original blue part.