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2 different vac readings?

m17davis

m17davis

New member
Ive always had a boost/vac gauge and this whole time I thought I was getting 4 psi of boost. Is that low? I just bought the Bluetooth obd2 and torque app. My gauge in my car reads 8 for vac while parked. The vac reading in the app says im at 24.5 Do I have a vac leak?
 


I would say there is a good chance. Where did you hook up the in car vac/boost gauge too in order to get your readings? In my 04 I see 11ish psi of vac when at idle so I would check all your hoses for leaks. Also 4psi of boost seems low if you have a 3.4, are you sure you are not dumping your boost? I only bring this stuff up just based on my experiences and I could be off on it but when I was dumping all my boost my gauge only read 4psi
 
4 PSI is way low. I am getting 9 psi on a 3.4 & feel that is low. Does your car feel like a dog?
 
I tied the gauge in right in the back by the firewall. on the line that wraps around the s/c and goes under the snout. it doesn't seem like a dog at all. it kicks it right in the ass when you get on it. isnt 8 psi normal for stock?
 
ya that boost number seems low stock is like 5-6psi, like they said you should be at around 8-10 psi... im at like 10-12 on a 3.0.. plus your vac seems off too it should be sitting at like 20ish at idle.(-20 inHG)

take a pic of where you tapped into, you should be after the supercharger like the lim
 
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I get between 8 - 9.5psi stock. Literally all I have different right now are my plugs and I have a ZZP high flowing catted 2.5" downpipe. And open cone
 


yes. its idling, engine running.. and the -24 vac is not in hg. I checked the settings. its in psi both ways. is there a way to see if its leaking at the T for the boost/vac gauge?
 


I lied. the settings are on psi but the gauge itself on torque app is in hg... I inspected the T in the vac line and it looks fine. I don't know what to do.
 
Isnt that line just picking up from afted the bbv? You wouldnt see any boost from there except from bleed off. Right? Boost would be created after the SC.. can you tap into the lim? Or before the bbv?

Also have you tried spraying all lines and connections with carb cleaner yet?
 
The only time my boost was reading low was when I had a bad boost bypass solenoid. But it wasn't only reading low, it was actually building only half the boost
 


I told you why... your tapped into a line that is on the bypass... you need to be after the supercharger where the boost is made
 
its not in the wrong spot. It is right between the T on the lim and the map sensor. on the back side of the sc. bill even said so in a thread on here.
 
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