OK, so the new bypass valve came in today...Yea! It was as easy as @
shaynek and @
taiguy said it would be.
Here are a few things I learned along the way.
#1 check your bypass valve on a somewhat regular basis. I suspect mine has been leaking for quite some time before ever popping a P0171 code. (you'll see why in a minute). There are several ways to check it, some are like Duh! but they may not be obvious to everyone so be nice.
Before I go any further though, here's what the normal newly installed bypass valve ops are.
Under vacuum = valve open, allowing uncompressed air to bypass the SC rotors and go directly into the intake manifold.
With no Vacuum (car off, the valves resting condition) or with little vacuum or during boost = valve closed, engine is now using SC compressed air.
I tested the new valve with a vacuum pump and it begins to open at ~5in/Hg (-2.5 psi) and is fully open at ~10 in/Hg (-5 psi).
Probably the easiest way to check it is to, with the car idling, pinch off the vacuum hose that comes from the rear of the SC and heads down under to the bypass valve. If nothing happens, i.e. the valve stays open, idle does not change and you don't hear a hissing sound stop....your all good, valve is working, at least has no leaks.
Another way to easily test it is with the car off, disconnect the hose from the SC and connect it to a vacuum pump, whether that's a real vacuum pump or your lips. (just don't suck to hard) The valve should open under the vacuum values listed above, and should hold that vacuum and not leak down.
You could also use a smoke tester, again a real one or a cigar/cigarette or whatever else you might be smokin' that day and gently blow low pressure smoke into the valve and and watch for leaks.
Removing the valve was easy enough, just not a lot of room to work. Thank God the SC didn't have to come off! You basically come in from the front with an 11/32" (9mm is close enough) socket on a long 1/4" drive extension, I also had a wobble head since only one nut is straight on. Once the valve body is loose, the other end of the rod will slip out of it's hole once the lever it connects to gets rotated in the full counter clockwise direction (basically opening the butterfly inside) you'll see what I mean, just look at the part I have circled in red, it can only come out and go in when the slotted hole lines up with that tang.
Curiosity got the best of me so of course I had to open it up and see what was wrong. Not 1 but 2 holes! That's why I'm thinking this has been going on for a while. What I noticed on the bottom side of the blue diaphragm, was a sticky substance that was covered in grit (Orange arrow). That grit, no doubt, came from the engine bay since that is on the "outside" part of the diaphragm that is exposed to atmosphere. So every time that valve pulls in, air from the engine bay and whatever is floating around in that air, comes in contact with the outside of the diaphragm and clings to whatever that sticky stuff is. Now we have an abrasive in the mix so it's only a matter of time until the diaphragm fails. Paging @
Edelbrock LLC (they must really hate me by now!)
Even with these holes, the SC produced and maintained enough vacuum to actuate this valve, but you could hear it leaking (now that I know what to listen for with the pinch test). So you have a somewhat "working" valve but a nice vacuum leak which is the source of the P0171 codes. It got so bad the last day I drove it, that I could smell raw fuel. The fuel trims were pegged from the ECU trying to correct the "lean" condition it was seeing. Even with the fuel trims maxed out, the AFR was still "reading" lean (15.5 - 17.5) at idle. I've attached a log if anyone is interested.
http://www.datazap.me/u/birdtrd/log-...&data=10-11-30
So there you go boys and girls, now go check those bypass valves!