I set out this afternoon to fix the loss of dash vents during acceleration.

I tested all three of the servo on the drivers side including the dual acting servo. All of them held vacuum with only minimal losses over the course of a minute. Just for sport I plugged and clamped the yellow line - no luck.

under a hard long acceleration I still lose the vents. talking like 15 seconds at 4,000 rpm, think climbing a hill, fully loaded with a cargo box on top.

I checked the check valve with the blow and suck method as well as with the might vac. Its solid. I checked the tubing system from the manifold to the firewall including all the rubber elbows and unions, although the have some surface cracks, the entire system held vacuum fine.

I understand how the system works: if the yellow line or its servo has a leak , the single acting servo that controls the dash vents will lose power and will default to the feet.

What should I be checking next?

Does anyone have a schematic of the vacuum system??

Could I run a line directly from the cabin side of the check valve to the dash vent servo control as a diagnostic?
Thanks,
matt


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