Low Vacume, full boost??

[Bmxr152]

My car is freshly rebuilt but has like only a -10 vacume and idles kinda iratically. When i hot boost though everything clears up!???? I have an open downpipe exhuast if that makes a diffrence. Also seems to be running rich, Whats the proper o2 voltage for idle and for WOT?? thanks in advance guys

 

[black93es]

Well, check all of your vacuum lines to make sure they are all stable and not sucking flat, either that or one of your vacuum lines isnt correctly connected or your have a crimp or a pin hole in a line. Check that, listen to see if hear a boost leak even though your gettin full boost. Hope I could help buddy, Good Luck!

 

[jeremy19984g63]

ya it does sound like a small vacume or boost leak. Does it idle a little higher than normal? if so its a vacume leak

 

[chris4g63t]

It could also be your cam timing(timing belt side) being off a tooth or so. This happened to me when I first put my motor together a year or so ago. I actually felt more top end when it was off a tooth. But make sure you check that.

 

[jeremy19984g63]

mine idles at -15 vac but its a 2g if that makes a difference

 

[oldman]

mine idles at -15 vac but its a 2g if that makes a difference

You probably have leaks, normal is -18 to -20 inHG.

 

[jeremy19984g63]

You probably have leaks, normal is -18 to -20 inHG.

i am using 8.3-1 pistons would that cause -10 -15 at idle?

 

[Bmxr152]

im using the same Wiseco 8.3.1 pistons, and it right about 700 or 600 at idle but idles like it has HKS 272 cams

 

[jeremy19984g63]

egr valve may be stuck open

 

[jeremy19984g63]

no never mind about egr

 

[erebusknight]

whats the background of that rebuild? you or a shop or what? Any sensors that may have been overlooked or broken off? If you can see your O2 voltage then check to see if front sits around 450mV. Seeing that you dont have the rear intact, its possible that it may be throwing a false signal to the computer. Is it just hanging there? in the old pipe?

 

[chris4g63t]

Elevation is a big factor but it should not be at -10, especially if you have stock cams. My fresh motor pulls -15 @ idle with stock cams. All my friends cars with 272's pull about -10. This is at 5000 ft though. When I'm at sea level it pull -18 to -19 @ idle.

 

[Bmxr152]

Alright here is my Data log pull look at the O2 vaoltage. http://www.cardomain.com/member_pages/show_image.pl?bg=FF0000&image=http://memimage.cardomain.net/member_images/2/web/2282000-2282999/2282369_17_full.jpg

 

[DSM90AWD]

Alright here is my Data log pull look at the O2 vaoltage. http://www.cardomain.com/member_pages/show_image.pl?bg=FF0000&image=http://memimage.cardomain.net/member_images/2/web/2282000-2282999/2282369_17_full.jpg

Yuck, part throttle knock What does your LTFTs look like?

Your low vacuume reading is consistant with what I'd experienced when my exhaust cam was off by one tooth (tends to rotate when instaling the T-Belt). Aftermarket cams with a longer duration can also lower idle vacuume, but not that significantly (my FP2s only brought me from -20 to -16).

I'd also run a compression test to check for leaking valves / HG / compression rings and perform a boost leak test of the intake

 

[black93es]

Well, even -15 vac isn't that good. Your car should always be running vac from -18 to -22 -22 being MAX and -18 being MIN, nothing lower or higher. -10 vac is NOT OKAY, neither is -15 but it's better than -10. Good Luck bro.

 

[oldman]

i am using 8.3-1 pistons would that cause -10 -15 at idle?

No, CR has very little effect on vacuum reading. If anything, higher CR should increase vacuum not decrease.

 

[chris4g63t]

Well, even -15 vac isn't that good. Your car should always be running vac from -18 to -22 -22 being MAX and -18 being MIN, nothing lower or higher. -10 vac is NOT OKAY, neither is -15 but it's better than -10. Good Luck bro.

Not true. Even brand new evo's only pull -15 up here. But he most likely has a problem with either his compression ie head gasket or piston rings, or with valve timing. I say this because a car usually doesn't run right with that big of a boost leak.

 

[DSM90AWD]

Not true. Even brand new evo's only pull -15 up here

I took it to mean in Bakersfield, CA not the Top of Everest

 

[black93es]

Not true. Even brand new evo's only pull -15 up here. But he most likely has a problem with either his compression ie head gasket or piston rings, or with valve timing. I say this because a car usually doesn't run right with that big of a boost leak.

...okay, well we're not talking about a "brand new Evo" now are we? Anyways, if you do a lil' research, you'll find that a relativley stock Eagle Talon TSi (Eclipse,Laser) for vaccum SHOULD BE RUNNING -18 to -20 vac, if I am wrong...show me proof I am wrong...which is doubtfull. Sorry but hey. And as for the person were trying to help, hows that goin? Iam gunna say check your cams, they may be f'd or whatnot. Good Luck dude.

 

[Bmxr152]

they dont exactly line up the exhaust cam is a line higher. is that right???

 

[oldman]

they dont exactly line up the exhaust cam is a line higher. is that right???

Your low vacuume reading is consistant with what I'd experienced when my exhaust cam was off by one tooth (tends to rotate when instaling the T-Belt). Aftermarket cams with a longer duration can also lower idle vacuume, but not that significantly (my FP2s only brought me from -20 to -16).

Take a picture and post it.

 

[Bmxr152]

Here is a picture of my cam gears... http://www.cardomain.com/member_pages/show_image.pl?bg=FF0000&image=http://memimage.cardomain.net/member_images/2/web/2282000-2282999/2282369_20_full.jpg

 

[dnhieu]

obviously your off about 2 teeth buddy....

also im experiencing -11 vacumme but i KNOW i got blown turbo seals and a slightly leaking pcv valve. i dont really understand the turbo seal one because my car boosts just fine and there is no oil in the intake but when i boost leak test from the intercooler piping the blow by goes away so i assume my turbo seals are bad. is this true? do you guys think between the seals and the pcv valve that im loosing -9hg?

i have done the following to fix.
boost leak test (none besides blowby)
compression test 165-170-170-170
all new vacumme lines
checked timing (right on)

thanks in advance
david

 

[chris4g63t]

Here is a picture of my cam gears... http://www.cardomain.com/member_pages/show_image.pl?bg=FF0000&image=http://memimage.cardomain.net/member_images/2/web/2282000-2282999/2282369_20_full.jpg

This is at tdc correct?

 

[oldman]

Here is a picture of my cam gears... http://www.cardomain.com/member_pages/show_image.pl?bg=FF0000&image=http://memimage.cardomain.net/member_images/2/web/2282000-2282999/2282369_20_full.jpg

How did you put it in TDC?