Bypass valve connection

[Tom @ Fast Forward]

Well, I may have an answer as to why there have been a few bypass valve failures. I think that connecting the vac/boost line to the valve from the intake manifold is a bad idea. The one on my 99 had a diaphragm failure last week. I have installed a new one and moved the hose to the VDB and it works just the same. However, the bypass diaphragm is no longer being punished with all that boost. The VDB only sees vacuum, driving the valve to bypass mode, and atmospheric pressure, driving the valve to boost mode.

I recommend this conversion to everybody. All I did was pick up a 1/4" Tee from the hardware store and cut one of the 1/4" lines going to the VDB. Install the tee and move the Bypass hose to it. Then either cap the bypass fitting on the manifold or remove it and replace with a pipe plug.

The operation will be the same but I expect the life of the bypass valve to be significantly extended.

[John Miles]

Thanks for the tip. I implemented this "ECO" today and found it worked well. It may be my imagination, though -- I seem to feel a slight nonlinearity at tip-in that wasn't there before, as if the bypass valve is keeping the blower out of the picture a bit longer than it used to.

Have there been any diaphragm failures at normal (circa 11 psi) boost levels? I may put it back the way it was, depending on how the throttle response feels at low speeds in stop-and-go traffic. But I won't if you feel there is a serious risk of damage to the bypass valve diaphragm.

Are we talking 1% of bypass valves failing in the field, or is it more common than that?

[Tom @ Fast Forward]

John,

Failure rate was not high. Maybe 10%. There is another thing you can try if you think it is moving too slow. There is a brass restrictor in the plastic nipple on the bypass acruator. If you remove it, the bypass will speed up. If you go back to attaching the hose to the manifold, you will need to replace that nipple as it helps protect the bellows in the actuator.