Low vacuum

[compression]

Why am I getting low vacuum at idle? I am only drawing about 10 inches of mercury(hg). Which seems to be about half of my what two of my friends pull in their WRX and EVO8. I have plugged all the major unused holes on the intake manifold.I rebuilt this motor from the ground up. I have confirmed what my boost gauge is reading with the reading from the MAP sensor that inputs to the EMS.ALso, my blowoff valve is not working. It is a greddy type-R (the big one). Are the springs in this valve stiffer than what the engine can pull? THe preload is all the way backed off. This could be a result of the low vacuum in the intake manifold.I am going to try using a type-s valve in a few days to see if that works.

survey:What vacuum do your cars run at idle?(about 1000rpm)thanks

[SpeedRacer1]

I run at about -70 kilopascal-0.7 Bar (not sure if these are the negative equivalants)-20.6 inches of merc

I am not sure what your vacuum equates too. But the Evo 8 runs up to 18 PSI stock, while SR's run at 7 max PSI stock. That might be the reason you find different results when comparing these engines.

[compression]

What the engine is boosted to is not important. Hearing that your SR is pulling about 20 inches of merc, and mine is pulling about 10 inches of merc, that worries me.I am going to have to do some trouble shooting tonight.what are other vacuum numbers are people running at idle?

[SpeedRacer1]

If it has a BOV the idle boost will be a little higher than mine . If the IACV is not working the idle boost will be lower than mine.

If your vacuum hoses are set up incorrectly you can end up with higher boost at idle. My friend used to have the same idle boost you do now. After changing the hoses his boost is closer to mine.

[chrispy]

mine is about .78 hkpa at idle

[BaliLover]

Around -18 or -20 at idle here

[VitaminT]

I don't get it. My car runs around 20psi vac at Idle. Is that not about 40 inches of mercury?

[Cyberkreig]

I run around -11psi at idle, depending on what my car feels like.

11psi = .75bar = 22inhg

[VitaminT]

Dang I pull 20psi at idle every time I take her out. Is that bad?

[RobDET]

i think he means -20 speed....

I pull -18 to -21 psi

Try unplugging your O2 sensor at idle and see what happens. My o2 sensor caused all kinds of problems untill i got it straight....

Also does it idle smooth?

[compression]

Thanks for all the replies. The car is running on the AEM programmable EMS, so the O2 is not messing me up. It idles smoothly and drives fairly well considering I tuned it myself and I dont have any experience tuning (it will be tuned soon by a pro).

Last night I plumbed the idle into the intercooler-to-throttlebody pipe (where the BOV is also). I drove the car around and it was phenomenal, the boost was almost instantaneous and it pulled much harder than it did with the idle tube open to the atmosphere (I am not using a MAF sensor, so I thought I could do this).I unbolted the greddy type-r BOV and put tape over the hole on the pipe. I was shocked to see this tape bulging out at idle, telling me that the system is under positive pressure at idle, weird.Speedracer 1, can you elaborate a little on your experiences?I have two vacuum hoses, one on each of the 2 nipples on top of the throttle body. One of the hoses (larger one) goes to the MAP sensor, the other goes to my BOV, Fuel pressure regulator, and boost gauge(mechanical). There are no other vacuum fittings on the manifold (no power brakes) except for the factory hoses that go to the valve cover(right by the ports).Any ideas why I am seeing boost at idle in the intercooler/piping system????I talked to a tech at AEM and he said set the ign timing to 20 degrees at idle, that should help. I will try that tonight.

[SpeedRacer1]

Well if the tape is bulging at idle then wouldnt that mean your BOV is leaking air at idle? If you are doing this and the engine is trying to maintain idle while losing air, couldnt the engine be sucking in more air than normal trying to make up for that lost air?

Perhaps, but probably not, besides you dont have a MAFS anymore.

As for what I have noticed, that pic is of my car at idle with the recirc and my IACV fully functional, stock = -0.7 bar. When I add a BOV the pressure moves to about -0.45 bar at idle. If I cut the auxilliery power to the IACV (I have a switch for this) the boost at idle will go down about -0.1 from wherever it was at before.

But you are running a different system from my stock one, with a MAPS, and an open IACV so I doubt this helps.

[Cyberkreig]

I have two vacuum hoses, one on each of the 2 nipples on top of the throttle body..... There are no other vacuum fittings...

You do know about that small vac fitting on the underside of the TB right?

[compression]

yeah, thats the one for the carbon canister, its plugged.

[240r]

I'm having the same problem to, only I have everything stock. I found out before that I was getting some leak through my BOV and maybe a little through my pipe, but I just replaced all my pipes and took my bov off and capped all the vacuum hoses off leaving only one for my gauge, but I am still only getting 10inhg. I think it might be leaking at my brake booster but I have not had time to get around to check that yet, because it does not seem to be working to good. My car is also idleing at around 2500 rpm. Do you guys have any input on this?

[compression]

I have done some more investigating and it comes down to the fact that it pretty much has to be a vacuum leak on the manifold. I was told to check ignition timing (?) but it is at 17 degrees which is just fine.The next step will be to remove the manifold, and tripple check every fitting and gasket and reassemble it.

The BOV is not working because when the throttle slams shut because it is not getting enough vacuum to raise the plunger, I have tried both a greddy type-s and a greddy type-r, both brand new.Anyway, hopefully i will find the source of the leak, I have a feeling the car will drive better when I do.

[gtune4]

mine idles at -17.7 to -18.9 inches of mercury or -.60 to -.64 hkpa.would you guys consider this to be enough??

[compression]

I have since fixed the vacuum problem, so the reason this post originated is dead. But to answer your question...

-17 to 18 inches at idle (850 rpm or so) is kinda low, is that the reading after the car is warmed up and idleing low? A Healthy SR should be at least 20 inches or merc at idle.

Have you had the cams out? THat was the reason mine was off, the cams were installed two teeth advanced. I could not get 20 inches at idle, I was always in the 17-18 range. then I fixed the cams and BAM!, 21-22 inches at idle, beautiful.

[gtune4]

could be my timing??cams are still untouched

[compression]

Yes check your timing(its quick and easy), and do a compression check and a leak down check, if you cant do these, then have a mechanic do it. These are the most important checks and will tell you if and where any loss of compression is occuring(especially the leakdown).If those dont reveal any problems, then THUROUGHLY check the complete intake manifold for any leaks. Look closely around the rubber o-ring seats for the injectors, also examine pcv hose that goes to the valve cover, anywhere air can be leaking.

Does the car run fine, just low vacuum?Is it making the Hp it is supposed to?At what RPM did you get those numbers?Did this just start happening?WHere did you get those numbers from?

[gtune4]

the car had 2 "brian farts" i guess in the past two days. when they occured, they were occompanied by low jumpy idle, about half vaccum, black smoke like a boost leak. checked everything, no leak? today, i cleaned all of my elec connectors from the ecu out and replaced the pcv valve, tightedned my bov a bit (sound better, less choppy), took the metal screw out of the idle air control valve (iacv) and sprayed carb cleaner in it, let it sit, started it up, repeated, cleaned the screw and used a little 100% silicon on the o ring on the screw (adjusts nicely). started it up and ran the cleaner through the motor. reset the idle ect... now i am getting between -17.7and-18.3 during the middle of a warm day. i imagine that it will go to -18.9 at night. the guy at HT said that 18 was ok. 20 was right on.

so what can cause this slightly low vaccum other than tiny hidden leaks i have yet to find?

timing is at 15 deg and idle is at 750 with approx -18.3 vacuum at idle.

why does my car occasionally have a brain fart. it has happened a total of about 10 times. acts funny, then stops acting up. (maybe after cleaning all that **** it wont do it anymore. i think it was a combo of my idler and bov?!?!?)

also, this all seemed to start when i took out the temp sensor for the gauge and put it back in (dont ask why), mabey i didnt bleed the sys enough?

**** it, it works :ylsuper

does it ever end.... not that i mind.... i love my car... i hate my car... i love my car....like my ex girlfriend?:D

[gtune4]

http://www.convert-me.com/en/convert/pressure

i dont know how long this has been here, but it helps me!