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I note that the vacuum, at idle, directly off the manifold of my 71 BB is only 17 and goes up to about 22 on acceleration. My headlights are sluggish and wiper door does not work. My question is this (1)is 17-22 enough vacuum to properly work system? and (2)if not what kinds of things could cause a lower pressure at the manifold? Thanks Ed
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Re: intake manifold vacuum
Ed------
17" of vacuum measured at the engine intake manifold should be adequate to properly operate all of the vacuum-operated components of your car. The fact that there is some problem with the operation of the components is much more likely related to the vacuum system than the amount of engine-produced vacuum.
For a 71 big block (assuming that it's an LS-5), I'd say that 17" is about right at idle. It might be a little bit low but, as I say, certainly not enough to cause any problems with the vacuum system. Engines lose a bit of idle vacuum over time due to general wear of internal components. But, if yours is 17" and steady at idle, I don't think that you have any significant problem with the engine. In fact, if your car were an LS-6, I'd say that 17" would be quite good.In Appreciation of John Hinckley -
Re: intake manifold vacuum
(1) Yes, that level of vac pressure is sufficient to operate the system and looks pretty good to me.
(2) Time to dig into the archieves, bone up on the maladies of Shark vac system troubleshooting and plan to set aside time to find/fix.
(3) Once you've researched prior threads (this subject comes up at least once a month) and have tooled yourself for the job ahead, my advice is:
(a) Set aside an entire Saturday--it's at least a one pizza/one 6-pack job.
(b) Don't expect to find ONE problem, troubleshoot the WHOLE system and find/kill all of the 'funnies'....
(c) It can be a rather fun/relaxing task if you go slowly.
(d) WHEN you find leaks, presume they've been there for awhile and your system's been invaded with airborne 'crud'. Therefore, plan on either cleaning the vac check valve or replacing it AND buy TWO vac system filters. These were intended to be replaced at least once a year and very few owners did this. When you find/fix leaks and replace your existing filter, the 'crud' that found it's way into the system is going to migrate back to the source and quickly plug up your fresh/new replacement filter. So, use the second one after a few months....Comment
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Re: intake manifold vacuum
Ed: The vacuum headlamp/wiper door system for your car is easy enough to trouble shoot once you know precisely how the system is designed to work AND you have a couple of simple, low cost tools. However, it is easy to begin replacing components by guessing what's wrong, spending lots of hard earned cash along the way, only to end up with a system that still only functions marginally.
There is a shortage of good reference material out there for these systems. Terry McManmon and I developed a technical course that we conducted for a couple of years at the Bloomington Gold Show for that reason.
If you send me an e-mail with more details as to what your system is doing I think I can help you locate the source(s) of the problem. It has been my experience that: 1) There are probably mutilple problems; 2) Components will continue to work (sort of) when they have problems (like small vacuum leaks) and 3) Bad hoses are rarely the major problem (though often times people start there).
Helping each other is what NCRS is all about!
My e-mail address is: AIR_LT1@hotmail.comComment
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Great reply!!! *NM*
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