the coupe performance has been lackluster at best. I had not driven the 300d for a while before I sold it and I couldnt drive the coupe until I sold the D. JackG stopped over to shoot the bull and I went for a ride in his D. man it ran a whole lot better than the coupe. Then Jack and I went around the block in the coupe and he was less than impressed. We decided the turbo was not working properly. After Jack left I decided to clean the banjo bolts to see if it would help. looked like the PO had recently done this. then I tried blowing through the line, nothing. I pulled the lines of the changover valve on the firewall and then I could blow through them so i pulled the changover valve. with 12v on it It did not pass any air. after a lot of clicks I got it to pass air, but out the top not the connector line. I took a runner hose and connected the ALDA and manifold lines together. Now the coupe runs very nice, good accell and nice take off. So what activates this valve? Is it normally open and closed with power or is it normally closed and open with power? Is the valve competely necissary?

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

there is a boost pressure switch on the intake manifold that IIRC sends said signal to the OPV(overboost protection valve)

I just bypassed it to clean up the mess of vacuum lines.. I know what my engine runs(I removed the boost gauge since it broke)

There is an electrical switch on the manifold that closes when the boost pressure reaches 15 psi. This is presuming that the switch still works and is not packed with soot like the banjo bolt.

When the switch closes, the overboost protection valve closes and the horizontal port is now connected to the top port. The ALDA is vented to atmosphere.

When the switch is open, the overboost protection valve is open and the horizontal port is connected to the bottom port. The ALDA is connected to the manifold via the banjo bolt.

The valve is unnecessary if you never have a wastegate failure and the wastegate always opens at the setpoint. The valve is also unnecessary if the manifold switch is plugged with soot and doesn't close at 15 psi (highly likely).

It seems like a good safety to keep this system intact. Where is the pressure switch located? Can it be cleaned and tested?

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)