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Old 05-24-2011, 06:25 PM   #1 (permalink)
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The Wagon - '91 Volvo 240 Wagon
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91 Volvo 240 vacuum guage

I bought a vacuum gauge for my 91 volvo 240 and installed it, first I hooked it up where the climate controls get a vacuum from but the guage would read 15psi at all times, I think its because of a check valve I had read about online which uses a different size hole than the tube for the guage or climate controls and drops to the size needed for the climate.

I found another vacuum hose hookup that I teed off of but I would only read a little under 5psi which would drop as a accelerated and return to 5 after I took my foot off the gas. Is it normal for one area to only have 5psi?

I noticed some nuts in the manifold that I'm guessing could be used with a compression fitting if I were to buy one. would this be the best option to get a proper reading on the gauge?

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Old 05-25-2011, 11:49 AM   #2 (permalink)
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Hi Goofee691,
On the top of the engine, a loop of steel tubing connected to the fuel line and the injectors is the fuel rail. Towards the front of the fuel rail is a pressure regulator that uses manifold vacuum. The regulator has a fuel return line, don't cut that. Put a tee in the regulator vacuum line for your gauge. The vacuum line is a slip fitting and smaller than the fuel return.

Also most vacuum gauges measure in inches of mercury. Air pressure is about 30 in of hg (29.92 at std...). So a vacuum will measure as about 30 in. on the guage. A car engine with a PCV valve will have manifold vacuum at idle of about 17 to 22 in. The Volvo doesn't have a PCV but does have a metered leak to vent the crankcase to the intake so idle vacuum is about 20 in. or a little lower depending on wear. As the engine powers a larger load the manifold vacuum drops almost to 0 at full throttle.

If your guage is in psi then the normal engine idle will be about 5 psi and drop to 0 at wot. But 15 psi is unlikely even for the vacuum resevoir of the hvac.

-mort
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Old 05-25-2011, 12:07 PM   #3 (permalink)
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sorry, my mistake. it is in inches of mercury not psi. I rode my bike to work so I cant look in the engine right now but I'll take a look at it when I get home.

the engine has over 220k miles on it to give you some indication of wear
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Old 05-25-2011, 12:56 PM   #4 (permalink)
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here are 2 pictures of the engine that I took a few months ago after cleaning it.

I'm not sure as to where you are indicating

http://hphotos-snc6.fbcdn.net/190969...7_708674_o.jpg

http://hphotos-ash4.fbcdn.net/194269..._7500948_o.jpg
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Old 05-25-2011, 08:56 PM   #5 (permalink)
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Thanks, that worked. reading good and working well.

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