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Where do I find what vacuum gage readings mean?

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Ray

05-11-2001 16:46:14




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An "older" mechanic I work with claims a vacuum gage is a great diagnostic tool to locate my 8N missing problem. Can anyone here on the board give me a leg up so I can act halfway intelligent Monday when I quiz him on specifics? My intake manifold has a small tapped hole above the carb to attach gage. I did a compression check a while ago.
#1 100 dry, 155 wet
#2 80 dry, 140 wet
#3 90 dry, 115 wet
#4 100 dry, 185 wet

What's the vacuum going to tell beyond that #3 valves are weak? That shouldn't cause my severe miss and lack of power.????

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Dell (WA)

05-11-2001 20:09:50




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 Re: Where do I find what vacuum gage readings mean? in reply to Ray, 05-11-2001 16:46:14  
Ray..... .seems rather obvious to me that you have a headgasket leak between cylinders 2 & 3. Suggest you replace headgasket and torque in proper sequence. Also check your cylinder head for "flatness".

I don't think a vacuum gauge can measure that..... Dell



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Ray

05-11-2001 20:18:26




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 Re: Re: Where do I find what vacuum gage readings mean? in reply to Dell (WA), 05-11-2001 20:09:50  
Dell, I'll take your word for it,,,,, but what is it that makes it obvious? I had a professor in college that wrote equations on the board to a point and then walked away with a flip of his hand saying the rest was "obvious". I wonder if I'll ever get to say that to a novice or if I'm always the student who is left with a dumb look on his face. :>) Thanks for your help! I'll take a look at the gasket this weekend.

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Dell (WA)

05-11-2001 20:28:39




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 Re: Re: Re: Where do I find what vacuum gage readings mean? in reply to Ray, 05-11-2001 20:18:26  
Ray..... .I had a calculus prof that used to drive me wild with essentially the same comment....."its intuitively obvious"...and it never was. (grin)

Generally speaking, anytime there is low compression between any 2 adjacent cylinders, always suspect "leaky headgasket". And the only way to verify is by removal and inspection, and while you've gott it apart, replace the head gasket anyways, the're cheep enuff. Its the warped cylinder head which is generally the cause of the gasket leak that you have to really inspect for..... .Dell

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bg

05-11-2001 18:43:09




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 Re: Where do I find what vacuum gage readings mean? in reply to Ray, 05-11-2001 16:46:14  
Try this site:



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Mike S

05-12-2001 05:30:16




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 Re: Re: Where do I find what vacuum gage readings mean? in reply to bg, 05-11-2001 18:43:09  
Great site. Wish it had been around when I had my 85 Grand Wagonner. I might still have it if I had a resource like this to have kept it running.



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or this one....bg

05-11-2001 18:45:40




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 Re: Re: Where do I find what vacuum gage readings mean? in reply to bg, 05-11-2001 18:43:09  



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Jerry WI

05-12-2001 12:36:25




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 Re: Re: Re: Where do I find what vacuum gage readings mean? in reply to or this one....bg, 05-11-2001 18:45:40  
What a great page. Thanks a lot.



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tlak

05-11-2001 18:27:37




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 Re: Where do I find what vacuum gage readings mean? in reply to Ray, 05-11-2001 16:46:14  
The way I read your compression test is #2 came up decent on the wet test so I would say it needs rings on that cylinder and #3 didnt come up very much so its a valve problem there.



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JimNC

05-11-2001 17:36:17




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 Re: Where do I find what vacuum gage readings mean? in reply to Ray, 05-11-2001 16:46:14  

Ray,
A vacuum gage reading will tell you if your intake valves are fully seating. I can't give you a specific reading but the gauge should hold pretty steady probably 12-15 Hg. If I had to guess I would say your valves are burnt. The compression is a little below min on #2. Min compression is 90 psi. But I've seen many engine running good with below min compression. I would concentrate on a valve train problem.
JimNC

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