scrip7

iTrader: (6)

Perhaps he's thinking 1.0 on the vacuum side instead of 10???....if the needle's going to the yellow "10" then that would at least be closer to normal. I would suggest making a trip to a parts store and get a common vac/ fuel pump gauge and post those readings.

MaczPayne

iTrader: (5)

Holy ****. That's like no vacuum at all.

Are you sure the boost gauge is hooked up right? Any vacuum leaks?

It's almost as if your engine was under load with no boost...

Spectator

iTrader: (1)

YEs I am sure its plugged in correctly. You cant really mess it up too. And I'm 100% sure I have no vaccum leaks.

Can my gauge be wack?

MaczPayne

iTrader: (5)

Possibly. I know mine is off by a bit, since my Microtech reads otherwise. But I trust that more than the gauge.

Polishammer

You can measure vacuum in any unit you want, even PSI, but it is very uncommon to see vacuum indicated in anything other that inHg. It is easy to see. If it says 30 then it is in inHg, ii it would be in PSI, the you would see something around -14.7PSI. It is physically impossible to pull vacuum to -30PSI
In your case, there are only two possibilities, your gauge is either broken or not hooked up correctly. If there is no vacuum at idle your engine will most likely not idle at all. Engine is nothing more than a pump, it sucks air. If you you push the air in (turbo) then you have to increase the RPM, otherwise the engine will stop.
At least that's what I think.....

Spectator

iTrader: (1)

Well. I just went home to see and examine stuff. I looked at my hose to see if it was kingked, it wasn't. I also shortened it. It takes the vacuum from the intake, on the firewall side, right after the TB. So I know its in the right stop.

Here is what I saw. At idle, its almost dead zero. When I rev the engine, the gauge reads vaccum up to 4 until boost comes along. Then it goes up to 6 PSI. I think my gauge is fucked up.

Wtf?!

CyberPitz

My gauge reads around 10 psi when idle....so I think yours is messed up.

FCKing1995

iTrader: (3)

If your vacuum reading is that low, you either have a vacuum leak (even though you say you dont) or your engine is a magician. It shouldnt really be able to run with that low of a vacuum. Autometer guages are pretty tough, so I wouldnt think youd have a bad one. Could be though. If it reads boost when you rev, then that makes it pretty clear to me that its working. It wouldnt read boost but not vacuum (I dont think anyway). So check for a vacuum leak again, even though you say your 100% sure. You can always overlook something. otherwise, I have no idea why youd have such a low vacuum. Like I said, I dont even think the engine would be running with 1 Inch of vac.

classicauto

iTrader: (3)

Pfft, if I lower my idle to 1200RPM on the HBP, I end up with about 3-4in/hg. Slightly more then the OP. So its no magic.

Where is your gauge tapped into for signal? As in, lower? upper? imddle port?

The ports on the rear of the UIM just after the thorrtle body are very restricted. The best port for clean vac signal is the upper port on the front of the UIM. It muffles the pulses enough to get clean signal but doesn't restrict them at all.

scrip7

iTrader: (6)

A streetported engine would show different vacuum at idle, but I don't think it should be zero. You wouldn't have a steady idle at 950 rpm if you had zero vacuum. Depending on how it was ported, there should be at least a small amount of "lope" to the idle, sometimes barely noticeable, sometimes quite noticeable with a large streetport, with an idle no less than 1000 rpm, again depends on the engine builder. A video or sound clip would be helpful. And did you go to the auto parts store and get a gauge like I mentioned in post #26? ....they're pretty cheap and accurate enough to help us help you. You can also try the propane torch trick to verify a vacuum leak, it's quick and cheap.

Polishammer

The engine will run without a vacuum, and even with positive pressure, but not at OEM idle.

scrip7

iTrader: (6)

Good point.

You could also "tee" into the vacuum line to the boost sensor with a known-good vacuum gauge.

RX7Tuner.

if there was a vac leak, you would see the needle bouncing not pegged at 1. My money is on a bad guage.

Aaron Cake

iTrader: (1)

Are you sure the boost gauge is not connected to a nipple before the throttle body? If that's the case, then it will read boost but very little vacuum...

Nipples at the front of the throttle body are vacuum, at the rear they are atmospheric.

TehMonkay

iTrader: (-1)

why are you idling at 950? Is your bac removed? Or have you just not bothered with it. How old are your vacuum lines and intake gaskets?

Spectator

iTrader: (1)

All gaskets are new, all vac lines are new.

I uses the large nipple right after the TB on UIM, firewall side. I wanted to use the nipple for the boost sensor but I already had a ''T'' fitting there for my BOV. Can I split it again? Or would that be bad, having 3 vaccum out of that small nipple only?

Spectator

iTrader: (1)

I will post a vid with sound so you guys can tell me if that thing is ported....Even people that know cars get in the car with me think its insanly fast...

I'm 99% sure the thing is not stock. I'm supposed to go to the drag strip next tuesday but I'm afraid. I dont want to pop the enigne.

dean23

i was worried about "poppin" my engine, so i got a wideband to keep an eye on things. i have that same gauge and my vac read at around 15inHg. if my car wasn;t in the shop i'd tell you how i have it hooked up. i believe its split with my BOV.

Comitatus

iTrader: (7)

My suggestion was going to be similiar to Aaron's. It sounds like you have it hooked up to a boost only source.

Take a picture of where your boost gauge is connected on your UIM. Post it up so we can confirm the correct place for you.

classicauto

iTrader: (3)

there's your problem.

Use the TOP one on the front set of nipples on the UIM.

Spectator

iTrader: (1)

Awesome. And what readings should I get with the vaccum if my engine is not stock?

Oh and again, Classic, you're one hell of a rotor head. Thanks man. What wine do you drink? I owe you a nice bottle with all the help you give me. PM me your body shop address and I'll send it out.

classicauto

iTrader: (3)

Well....the readings will vary. But basically the scale is less vac=more port. Assuming equals between engine health/compression. (ie. a weak stock port engine will have lower vaccum, even though its stock port etc. but compression as you know will tell you health)

Honestly if its in the 15 range it could be stock port, could be street port. Its impossible to tell without opening it up. Even the "brap" effect can be had on a stock port engine with enough resonators on the exhaust (my TII did this with a stock port and crazy custom exhaust) so its really a crap shoot. Best way to tell (and only really accurate way) is crack the bee-otch open.

Since truly, if its pulling in the 15 range then you can rule out a BP of any type - you're only going to have a streetport at maximum - and the vac is goign to be so close to stock that its going to be hard to say.

What I'm getting at is I have no idea

Oh, and don't sweat the wine. Maybe we'll meet up at the Ottawa meet in the spring and have a drink. I'd like to think I know stuff - but really......I don't know anything.

Aaron Cake

iTrader: (1)

All nipples on the rear of the throttle body are atmospheric! I can't count the number of times someone can't get their standalone running because they connected to one of those nipples and it fires the first time after I swap to a proper vacuum nipple. OK, maybe I can. It's 3.

Spectator

iTrader: (1)

So can I split the Boost sensor nipple in 3? Meaning, Boost sensor, BOV and boost gauge from the same spot?

classicauto

iTrader: (3)

It *should* work.

But I generally wouldn't recommend more then one "T" into the pressure sensor signal..........but it should work.