KB guys...bypass valve question.

[davidbcasey]

I have been pulling my hair out chasing a vacuum leak and couldnt find it. Well, today I was checking out the bypass valve as a possible issue and noticed that the valve arm stayed extended even with the car running. I could manually compress it (open valve) and my boost gauge would go from 5" vacuum to 11" vacuum. That was a good sign...so I then removed the vacuum line from the valve and plugged it. My boost gauge then registered 21" vacuum! I found my issue...but, is it a bad valve or the known issue with KB BPVs with alignment/adjustment? I am leaning to bad valve since it doesnt appear to hold vacuum. With the car running I would push the arm up into the valve and it would stay but as soon as I killed the engine, the valve would slam shut...no leakage of vacuum to slowly close the valve...it was an audible slam. So, it appears that I have to remove the damn blower again...unless I can get this thing off and back on with it in the car.

Any help would be appreciated.

 

[redfr03svtsnake]

Is the problem low vac or is it a vac leak cuz if there is not enough vac due to another issue ( in my case iac being faulty) the bypass valve will not stay in the default idle position. My car for whatever reason is only getting ~11" vac but my valve is staying open, however since the iac isn't allowing enough fresh Air past the tb my car is starving for air @ idle, it has to be set at 1050rpm to keep it running. I guess what im asking to make sure that its a vac leak thats causing low vac not something else...The only reason I suspect the iac is that my pcv hose is getting crushed, meaning that the normal source of fresh air is not there and it's trying to breathe via the pcv. The reason I'm asking you this is cuz according to Kenne bell you need at least 10-12"vac to open the byPass. Obviously it's not opening or closing properly but it might not be functioning properly due to the low vac.... Hope this at least sheds a Lil light on it or maybe a thing to check

 

[davidbcasey]

Yup...I was thinking along those lines as well, but when the vac line is connected to the bypass my gauge reads ~5" vacuum in closed position. If I force it open, the gauge jumps to 10. If I remove the line and plug it with my finger, the gauge jumps to 21" where it is supposed to be. Makes me think the bypass is faulty. I have looked everywhere for a vacuum leak and just cannot find it. I am hoping that replacing the bypass fixes my leak. The bypass also makes a strange noise which will stop if I grab the plunger. I read on here about KB bypass alignment issues...sucks.

You sure your bypass is staying open? Have you taken the vacuum line off and plugged it with your finger and checked what your gauge reads?

Thanks for the input.

 

[redfr03svtsnake]

i have a feeling that my bypass might be my issue as i swapped my iac with a buddies off his cobra and this issue was the same, so im going to try your method.... hopefully that is it.... any update on urs?

 

[Silver03Termi]

Faulty by pass valves can be catastrophic. The blower moves more air than the motor uses at idle, hence why the valve is open at idle. Sadly, the fail position for the valve is closed. If you have the valve closed, the motor running at idle, and you open and close the throttle, you create waves of pressure colliding with one another. Cavitation. This will wreak havoc on your blower. Replace the valve. I'm not sure about the kb's, but on my whipple, i had to take the blower off, and dismantle the discharge plate. The part was about 70$. You can test the valve by getting a hand vacuum pump and placing it on the valve and seeing if it holds vacuum. Hope this helps. Good luck.