Vacuum reading

G

Guz

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Jul 15, 2009

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Winter Garden, FL

Nov 17, 2010

#1

• Nov 17, 2010

• #1

I just installed a vacuum/boost gauge on my 04 Vortech mustang. The reading I'm getting at idle in park (auto trans) is 29. Could this be an indication of a leak somewhere? I used the vacuum line that connects to the plenum. Also if I rev the engine in neutral should I be getting a boost reading.

 

wmburns

SN Certified Technician

Aug 14, 2009

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Nov 17, 2010

#2

• Nov 17, 2010

• #2

29 what??? Inches of mercury, PSI, Kpa?

Do you get a boost reading if you drive it? Where is the fuel pressure sensor vacuum reference connected? Would think the same line should be used.

 

sneaky98gt

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Apr 23, 2008

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Nov 17, 2010

#3

• Nov 17, 2010

• #3

29 is actually relatively high, I think. I get about 20 inches at idle. I will see a little bit of boost in neutral, but not much, maybe 3 pounds. The motor has to be under a load to make much boost, especially with a centrifugal supercharger like a Vortech, and the motor isn't under much of a load when it's not in gear. Is it making boost under a load, like a 3rd gear pull/torque converter locked up at 75?

Also, what do you have your boost gauge hooked up to?

 

G

Guz

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Nov 17, 2010

#4

• Nov 17, 2010

• #4

29 In.Hg

 

G

Guz

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Nov 17, 2010

#5

• Nov 17, 2010

• #5

I get no boost in neutral.

 

G

Guz

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#6

• Nov 17, 2010

• #6

I used this same location

 

sneaky98gt

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Apr 23, 2008

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Nov 17, 2010

#7

• Nov 17, 2010

• #7

Guz said:

I used this same location

Click to expand...

Ha, I had the same problem. Here is my own answer to the same problem you have (not making boost):

sneaky98gt said:

Nevermind, got it fixed. Turned out that I had the boost/vac gauge hose in the wrong spot. I originally had it on the nipple used for vacuum diagnostics.(This is where you have it hooked up) The vacuum part of the gauge worked fine there, but apparently the boost part doesn't. So I moved it over to a hose coming directly off the top of the supercharger, and voila.(I don't know if you have somewhere like this also, but I would try splicing it into some other part of the vacuum harness) Everything works perfectly now.

It's actually making upwards of 8 pounds of boost, which makes me happy. More power for me.

Click to expand...

Hope this helps.

And just to be sure, are you making boost at WOT while in gear?

 

trinity_gt

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Jan 31, 2003

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Nov 17, 2010

#8

• Nov 17, 2010

• #8

29inHg is just about a perfect vacuum which isn't possible on a gasoline engine at idle. If there was a perfect vacuum in the plenum the engine would be getting no air.

What does the gauge read with the engine off?

 

G

Guz

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Jul 15, 2009

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Nov 17, 2010

#9

• Nov 17, 2010

• #9

It reads 0.

 

G

Guz

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Nov 17, 2010

#10

• Nov 17, 2010

• #10

sneaky98gt said:

Ha, I had the same problem. Here is my own answer to the same problem you have (not making boost):



Hope this helps.

And just to be sure, are you making boost at WOT while in gear?

Click to expand...

Where exactly should I hook it up?

 

G

Guz

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Jul 15, 2009

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Nov 17, 2010

#11

• Nov 17, 2010

• #11

This is my engine bay

 

midnightdriver

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Jan 3, 2010

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Nov 18, 2010

#12

• Nov 18, 2010

• #12

I think the spot you had it is ok, according to several threads I have read. Why are you trying to get boost in neutral? The engine has to be under load to really build boost. Especially centri and turbos.

Like sneaky said, What is you boost under LOAD, it the gauge reads zero than its mostly likely wrong. As you drive down the road what does the gauge do? How did you tap into the vacuum lines in the area?

Looks like you simply pulled on of the red lines out of the rubber connector, right? Could there be a leak it you tore the rubber? Check and maybe zip tie the lines on there.

 

midnightdriver

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Jan 3, 2010

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Nov 18, 2010

#13

• Nov 18, 2010

• #13

Would this line work? I know it gets vacuum and I assume it would definitely get boost but I don't know.

 

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trombonedemon

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Jun 25, 2009

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Nov 18, 2010

#14

• Nov 18, 2010

• #14

You should be reading between 19-21 Hgs. Make sure your line isn't pushed all the way in or backed out to far. That's an ideal spot for the vacum gauge.

 

G

Guz

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Winter Garden, FL

Nov 18, 2010

#15

• Nov 18, 2010

• #15

So i called the shop that works on my car and they tell me to tee the line at the fuel pressure sender on the fuel rail. Where exactly is this line?

 

Sonic04GT

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Nov 1, 2009

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Nov 20, 2010

#16

• Nov 20, 2010

• #16

Guz said:

So i called the shop that works on my car and they tell me to tee the line at the fuel pressure sender on the fuel rail. Where exactly is this line?

Click to expand...

I'm a noob, but I'm going to guess right here.
That's my beautiful stock motor btw

http://i295.photobucket.com/albums/mm142/thealmightyhubbard/IMG_0862-1.jpg