Steve here in Nevada . I’ve just purchased a 79′ Mark V . It’s got a few vacuum leaks . The headlight vac. cans have been rebuilt and lines have been replaced . The headlight doors still open within a minute or so . I built a “smoker” (boy did it !) . I could see no smoke from any lines inside or out .I isolated the engine vacuum and put a vacuum gauge and the needle is rock steady @ 14″ (late timing is what it says on it’s face) . I hooked the lines back up to the system and it still reads @ 14″ steady as the first test . I sure appreciate your site.
Thanks in advance,
Hello Steve –
Do you have a FoMoCo shop manual? To diagnose most devices on a luxury vehicle properly the correct manual is needed.
Does your Mark have the Autolamp option? If it does have this option, a vacuum module will be located behind the left kick panel trim. This module has three vacuum lines to it and a valve inside that can leak and are hard to detect with smoke I would think. There is also a vacuum valve located under the hood on all models that when the engine is not running can bleed vacuum back to the engine if it is faulty. The possibility also exists that your rebuilt vacuum servos could also be leaking somewhat. Any suspected component or components must be tested to know for sure as vacuum can leak wherever it is routed. We also find that many systems on our customers vehicles have more than one or two vacuum leaks. We have most parts and the correct service manuals available if and when you need them.