[fircrest]

Low vacuum reading?

Hey all,

I have a question regarding my vacuum pressure reading on my 2004 fxt. Today I installed an autometer phantom series boost gauge. The install went great so there are no questions there. My only problem is that I'm seeing a low reading on my vacuum pressure. At idle the needle sits at a steady 15. If I blip the throttle it goes up a tad, drops to 18 for a sec then goes back to 15. When the car is off it sits at 0 and at WOT it'll go up to a tad over 11 (right where it's supposed to). When I turn the AC on it'll go up to 14ish. The car is still running a stock map but I've upgraded the intake, tmic (w/ samco hoses), and cbe. I've listened around for vacuum leaks but so far I haven't heard anything. The car runs fine but I'm kind of worried I might have a problem. Any input? TIA

 

[wakeabyss]

What unit of measure does the gauge use while in vacuum? Also, is the engine to temperature or cold when you checked it?

 

[fircrest]

Here's a pic of the gauge:

I thought that it was because of the temp being cold so I drove the car around for a little bit to let it warm up but it still read at 15-16. Right now it's around 25 degrees here but I doubt that has anything to do with it. Maybe I used the wrong T section and tubing for it, I have no idea but it's bugging the hell out of me.

 

[fircrest]

I just read that a higher elevation will lower the vacuum but I'm a bit weary about that one...

http://www.wrxtuners.com/forums/f75/vacuum-idle-19700/

 

[wakeabyss]

I wouldn't worry too much, mine at idle reads around 17 in-Hg

 

[fircrest]

Alright, I'll keep that in mind. I'm still a bit worried though, what are some good places to start looking for vacuum leaks?

 

[fircrest]

bump?

 

[Tuned200]

My old and sold Nissan with SR20DET would pull about 15-18 on vac. Sounds normal to me.

 

[petermarksmith]

Hey all,

I have a question regarding my vacuum pressure reading on my 2004 fxt. Today I installed an autometer phantom series boost gauge. The install went great so there are no questions there. My only problem is that I'm seeing a low reading on my vacuum pressure. At idle the needle sits at a steady 15. If I blip the throttle it goes up a tad, drops to 18 for a sec then goes back to 15. When the car is off it sits at 0 and at WOT it'll go up to a tad over 11 (right where it's supposed to). When I turn the AC on it'll go up to 14ish. The car is still running a stock map but I've upgraded the intake, tmic (w/ samco hoses), and cbe. I've listened around for vacuum leaks but so far I haven't heard anything. The car runs fine but I'm kind of worried I might have a problem. Any input? TIA

I don't think you have a problem.

1. A/C usage requires more power which means more throttle opening - correlates.

2. The drop to 18 when you blip the throttle is exactly what mines does (i.e momentary drop and then back up to standard idle position - it's caused by engine over run on the idle speed).

A lot of vacuum behavior I have concluded is due to the nature of the throttle body not longer being directly controlled by your foot (i.e. via a cable) but via a whole bunch of electronics starting with the accelerator sensor... therefor it may not seem rational at times.