vacuum and bov leak

[winterftbl]

SO i have heard that normal vacuum is 15-18. Mine starts at 25 and drops to 30 between shifts. So I did a boost leak test and the only leak was by my greddy type s. Could this be the problem why my vacuum is so high. Thanks Winter

 

[winterftbl]

anyone?

 

[TalonTSIawd1991]

Your BOV shouldnt be leaking at all, fix that first then check your vac. again.

 

[LocknessMonster]

I had a similar problem with my greddy rs. Couple of the screws where loose on it that hold the two peices together. I would just go over the bov and make sure that nothing is loose.

 

[Talesin]

Manifold vacuum that high sounds like either jumped timing, or a broken vac gauge. A boost leak will not affect your vacuum. A vacuum leak will drop it (and 15in/Hg is low vacuum unless you're cammed or well above sea level). Only thing that will *actually* raise it, especially that high will be mechanical timing being WAY off (timing belt jumped teeth) or being at an extremely low altitude. Our cars should idle at around 20in/Hg at sea level, just for reference. At 8,000', mine would idle at 16in/Hg. Normal driving sees around 18-20in/Hg with a jump to 22-23in/Hg while engine braking, again at sea level.

 

[winterftbl]

Well i know that my belts are fine cause I just checked them. Could a leak be from the exhaust manifold cause I just found out that one of my bolts is missing?

 

[Icarus]

Only thing that will *actually* raise it, especially that high will be mechanical timing being WAY off (timing belt jumped teeth) or being at an extremely low altitude. Our cars should idle at around 20in/Hg at sea level, just for reference. At 8,000', mine would idle at 16in/Hg.

I wasn't quite sure if you meant higher as in lower pressure, but usually pressure decrases as altitude increases. So you see lower pressure at high altitude. Approx. -12.5"/Hg per 9,000'. But that's just the general rule subject to changes in weather and such.

Talesin is absolutely correct about the possiblity of there being something mechaincally wrong with the engine. That is the only way to get dramatically lower pressures at sea level. Considering you both are from around LA his pressure readings should be pretty close to yours.

I would check that timing again.

 

[winterftbl]

Well when I start my car my gauge will read 20, but then in a couple of seconds it will drop to 25-28. So maybe my boost gauge is off. This problem has only started since I installed my 16g. So then there is no way I have a vacuum leak?

 

[Talesin]

A vacuum leak will make you read LESS vacuum, not more. A vacuum leak you'll show 10-15in/Hg with an average leak. You're getting way too MUCH vacuum (30in/Hg)... FAR more than our cars are supposed to provide. Again, timing being off sounds like the only thing I can think of, assuming the gauge isn't broken. Check your timing marks.

 

[16gpoweredgsx]

Also, check to make sure your vacuum lines(especially the one for the boost gauge) are not pinched.

 

[Icarus]

A vacuum leak will make you read LESS vacuum, not more.

More vacuum = less pressure. A leak will equalize pressure/vacuum to atmospheric norm.

I think Talesin is correct on this matter, check your timing.

 

[Talesin]

The vacuum line being pinched would again read less vacuum. A boost/vac gauge exposed to open air should read at zero. It's calibrated to an atmospheric normal. When you apply vacuum (negative pressure as compared to ambient normal), it moves into the vacuum portion of the gauge. When you apply positive pressure (positive pressure as compared to ambient normal) it moves into the 'boost' portion of the gauge. A leak or line restriction (such as a 'pinched' line) will cause it to read closer to zero, NOT further toward the vacuum side of the dial.

The only way to read MORE vacuum is to either have a broken gauge, or to actually apply that amount of vacuum to the gauge. A vacuum/boost leak WILL NOT do it. A kinked line WILL NOT do it. Period. Either of those conditions will show less vacuum... more toward the zero-point on the gauge, as a leak will allow ambient air to equalize the vacuum slightly, and a kink will not allow the air in the lines to go past it (keeping ambient level air in the gauge-side of the lines).

Skipped/retarded mechanical timing, usually the cams, is the only thing I can think of that would cause MORE than ~22in/Hg of vacuum on our cars. And reading the OP's location... Santa Ana is pretty much at sea level (a quick google says 110' above sea level), so he should be seeing the same numbers I get, without having jumped timing a tooth or even two (or if he has adjustable cam gears, having the securing bolts slip).
REALLY needs to check that ALL of his timing marks line up, with a straightedge to the middle of the cam gear bolts and cylinder 1 at proper TDC. Not sure if he just looked at the belt and said 'yup, still on there', or hit it with a timing gun (ignition timing is NOT mechanical timing!) or what.

 

[16gpoweredgsx]

"Pinched vacuum line"

My bad, Talesin & winterftbl. I was thinking of fpr gauge. Was doing routine maintenance/check-up on my car right before that post. Sorry for the mis-information.

 

[123212321]

I just want to add that a vacuum of 25 when cruising at an RPM above idle is not bad. As your RPMs go up, as long as you are out of boost, your vacuum will increase as well.

 

[winterftbl]

Thank you guys for the responses, i am going to check my timing. Thanks again