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[Patrick]

I would just like to make sure that I am talking about the same thing. I was thinking about the pressure sensor that is screwed into the pipe leading to the intake just before the throttle.

The wire that leads to this must be lead to ground when raising boost. Just make sure you have a boost gauge and a lambda meter.

For those of you that doubt me: check out my web page.

L8ta
Patrick

[Rick MacLaren]

Hi Patrick,

I don't doubt you at all. I think we're talking about the Boost Pressure Cut Off switch. It is wired into the brain box and cuts off the fuel pump relay should boost exceed 20 or 21 PSI.

The switch itself 'can' be grounded, but does not 'have' to be grounded, when you increase boost. It all depends on HOW MUCH you intend to raise boost pressure.

The rationale for keeping it alive, or bleeding off pressure rather than grounding it, is that it does serve an important safety function. It prevents overboost. Preventing overboost saves the head.

Keeping it around, for me, is a low cost safety feature, besides, I don't intend on taking mine beyond that limit (again).

But your point is well taken, it is not necessary for the running and daily operation of a modestly boosted system.
_________________
1980 Porsche 931 Bitched.
1979 Porsche 924 Tweaked.

[ This Message was edited by: Rick MacLaren on 2002-01-19 08:19 ]

[TroyDest]

Hey everybody, relocate your overboost switch. The problem with the switch is that it is located upstream of the throttle body. In between shifts, the pressure in the upper tube spikes up because the throttle is slammed shut. As soon as the switch sees that pressure spike, it kills the motor. This happened on my car at only 12 psi boost. It doesn't do it at 7 psi boost because the pressure spike doesn't reach 1.4 bar.

Rather than remove the switch and lose the safety feature of it, just relocate it downstream of the throttle body. By doing this, the switch doesn't see the pressure spike but will still protect the motor if for some reason you get 1.4 bar of boost in your intake manifold.

You can tap a new hole in your intake or you can even tee into one of the hoses coming off the intake. Keep in mind that the switch housing must be grounded.

I tee'd into a hose and am running 15 psi boost with no problems. If I get stupid and turn my boost up past 1.4 bar or if my wastegate fails, the switch will still kill the motor as soon as it sees 1.4 bar.

[Rick MacLaren]

I like you.

You live dangerously.

[numbers]

Troy, I think you have the right idea. I have the same experience with the pressure spikes, and tried to solve it by cutting down the orfice on the switch. However, it still cut the engine on up-shifts, so I ended up grounding the switch wire. When I put my car back on the road in April, I will try relocating the switch.