boost gauge issues

[napkinthief]

ok well i got this boost gauge, autometer phantom, and it was reading -16 when the car was off and all messed up numbers. I modified it and now it reads 0 at off, -20 after i rev, but it slowly goes back to -15, i got a small clip take a look and lemme know whats going on...i really dont want to have to get another gauge if i dont have to..


EDIT

wont let me upload here, heres a link

http://www.mysharefile.com/v/8380972/2_1_0125061218.3g2


its a quicktime file taken by a camera phone, you can hear how my car sounds too, but the sound and the video are off

 

[nicknorth11]

vid's not working for me. vac should be around -15 - -20. after it makes it's way to -15, does it stay there until you get on it again?

 

[Dream On]

Looks like its working, but I'm not sure if your vacuum is what it should be (its hard to tell from the video). I would do a boost leak test and see if that changes anything.

 

[dalatinromeo]

vid's not working for me. vac should be around -15 - -20. after it makes it's way to -15, does it stay there until you get on it again?

Yeah you should be around -15 to -20. Yeah what happens after you get on it. Is your vaccumm reading consistent when at idle or surging?

Stay boostin

 

[hereitcomes]

this is correct. Vaccum should be at least -15 to -20. The correct reading is actually -19hg so thats close enough. stomp on the gas quick with the car in neutral, the gauge should jump to 0 at WOT and then come back to its vacuum position.
The best, and most accurate lines that Ive tapped into were the BOV lines, as there is always constant vaccum here.
Check to make sure that all of the fittings in the gauge are tight, and it is not leaking any pressure.

 

[oldman]

Yeah you should be around -15 to -20.

Actually, vacuum should be between -18 to -20, -15 to -20 is a huge difference. My vacuum was at about -15, after fixing my TB shaft seals, BISS screw o-ring, 2 injector seals and the adjustment screw on my Aeromotive, I now idles perfectly at -20 inHG/750rpm, absolutely no surge what so ever, maybe 50rpm when the my slim lines come on.

 

[dalatinromeo]

The best, and most accurate lines that Ive tapped into were the BOV lines, as there is always constant vaccum here.

I always believed the best place to tap a boost gauge was off the fuel pressure soleniod. Thats where I tapped mine into.

 

[oldman]

I always believed the best place to tap a boost gauge was off the fuel pressure soleniod. Thats where I tapped mine into.

You're correct. The BOV line is not at all the best place for the boost gauge. In fact, the BOV line should not be used for anything else but the BOV, especially the mbc.

 

[dalatinromeo]

Ok, just making sure since that where I had mine tapped, and had consistent -18 readings.

 

[Spaniel1287]

when your car is at idle, what is it supposed to be reving at? Just curious ### mine idles at 1100. SHould i take it down?

 

[dalatinromeo]

I have a consitent idle of 800 RPM's. I would say 1100 is kind of high. I would lower it a bit.

 

[napkinthief]

ok sorry guys, some misinformation here.

i am nt, and have no boost yet, just got mt t3/t4 today, need a manifold and im turbo.

the gauge is tapped into the egt on the back of the intake manifold, before the pressure release? valve.


the gauge reads steady at -16 at idle
when i press the gas WOT, it goes to 0 and stays there, but if i hold it, it will slowly drop down
when i release the gas, it drops to -20,-21 then slowly goes back to -16

 

[oldman]

when your car is at idle, what is it supposed to be reving at? Just curious ### mine idles at 1100. SHould i take it down?

Stock ECU is set at 750 rpm, what is your vacuum reading at idle?

 

[DSMcrazy3]

the gauge is tapped into the egt on the back of the intake manifold, before the pressure release? valve.

You must mean EGR vacuum line?

when i press the gas WOT, it goes to 0 and stays there, but if i hold it, it will slowly drop down

That's what mine did it would make it to about 3 or 4 in/hg by the time I would let off..None other than Oldman himself told me that it was a normal occurrance and that free revving is not good for the motor at all, so stop doing it.

 

[oldman]

ok sorry guys, some misinformation here.

Damn 420a, don't you guys have your own forum.

Vacuum is created when your engine's ability to consume air exceeds it's ability to supply air at a given throttle plate position. Two factors, assuming the system is leak free, determines the vacuum reading.

1. Throttle position, the more it opens, the more air supply.

2. RPM, the higher the RPM, the higher the engine consumption.

Given above, we can now apply it to your situation.

when i press the gas WOT, it goes to 0 and stays there

Throttle open, fairly low rpm, supply = or > then consumption, 0 vacuum.

but if i hold it, it will slowly drop down

Engine begins to out flow the open throttle as rpm increases, increase in vacuum.

when i release the gas, it drops to -20,-21

Throttle closed, high rpm, can't breath..........high vacuum.

then slowly goes back to -16

I think you get the point and I hope this made up for the "misinformation" so please don't report me.

 

[Spaniel1287]

when im ideling, my vac reads -19, -20 vac

 

[oldman]

when im ideling, my vac reads -19, -20 vac

http://www.vfaq.com/mods/BISS-2G.html