Welcome to the SR20 Community Forum - The Dash.
SR20 forum logo

Thread: Vacuum leak, but not a boost leak? Possible?

+ Reply To Thread
Posts: 21-27 of 27
2012-10-24 20:40:24
Ok I will give this test a shot.

I know my Pcv valve is functioning because I checked it two weeks ago.

I'll ask around for a compression tester.
2012-10-25 00:47:18
So i pulled off the breather filter and looked to see if any smoke came out. I didn't see anything noticable and I bumped up the RPM's some.

There was also suction when I covered that port so I'm guessing that means the PCV is working fine.
2012-10-25 00:55:42
I dont know how accurate this is or if this helps but I found this during some research, maybe you can find it useful

Idle 16" - 22" steady Healthy
Idle 14" - 20" steady Fair but worn
Snap throttle Jumps to 2" then on decel moves to 25" Healthy
Snap throttle Jumps to 1" then on decel moves to 22" Fair but worn
Idle 8" or less Vacuum leak, loose intake manifold
Idle Fluctuated between 14" - 19" Worn valve guides or head gasket blown between 2 cylinders
Idle Reading drops from normal Burnt valve, valve stuck open, misfiring spark plug
Idle 8" - 14" Valve timing incorrect or large camshaft overlap
Idle 14" - 16" Ignition timing wrong
Idle Moves between 12" - 16" Idle mixture incorrect
Slow engine speed rise Needle falls then rises suddenly Blocked exhaustWeak valve springs
3000 rpm Needle fluctuates and worsens with higher rpm Weak valve springs

Using a vacuum gauge
2012-10-25 01:40:01
yeah if your getting suction then your pcv and more than likely ring lands are still fine and your low vac is caused from somewhere else.

I do know with S4 cams or similar vac at idle on average is 14-16"

That source obviously doesnt take into account any type of damage such as ring lands but broken lands will result in lower readings as ive seen it many times both on my old motors when i was overboosting the t25 and cracked and broke lands. My vac depending on the sevarity would end up around 10-12".
2012-10-26 13:14:18
Check your cam timing. The engine can still run good being off by one tooth and will affect your vac.

Also check the lines going to your gauge and you can check the gauge also.
Last edited by kevwal on 2012-10-26 at 13-18-30.
2012-10-26 19:06:35
Boost leak tester will be your best friend at this point. It will narrow any possible leak down in the system.
2014-09-05 20:57:53
Sorry for bumping the dead :P

I have the same issue, low vac -10 at idle and I've been thru three engines and had it. The car is at 5,280ft and performs like it should, pulls hard at 15psi. I have went over the car tightening clamps, switching all vac lines and done the whole soap water thing, checks out...

Was there any resolution @OP ?
+ Reply To Thread
  • [Type to search users.]
  • Quick Reply
    Thread Information
    There are currently ? users browsing this thread. (? members & ? guests)

    Back to top