i get somewhere between 14-16 on my vacume. is that normal? i have a 93 with 34k miles and DP,MP,CB,intake,Pettit ECU.
thanks

 

Yep, sounds good to me.
~Tom

 

My vacuum at idle is around 18. Forgive my ignorance but, what exactly does this mean? what would cause a discrepancy ?

 

If you don't have any vacuum leaks:

* Normal stock motor will show 18" or better.
* Mildly ported motors show 14"-16".
* Heavily ported motors can go down to 10"-12".


Mine is around 20 (on the 19 side).

 

Mine dives to -22 on deceleration, 18-19 normal idle. Is there ever a driving condition where the needle should/can be at "0 psi", other than engine shut-off?

 

Other than shutoff, 0 psi also occurs under slight load. Where a full load would read full boost, a slight load may read 0 psi. For example, mild acceleration (light load) with little or no boost may give a 0 psi reading. But this reading would be only temporary until more load is applied or the load is decreased.

 

Any Idea what low vacuum pressure would be an indication of, if anything on stock motor ?

 

Possible vacuum/boost leak.

 

Apex seals giving out will cause lower vacuum as well.
~Tom

 

Idle speed and gauge error also play a large role. Higher idles will raise your vacuum and lower idle lowers it, up until a certain point (that no idles at) then the turbos take over and counteract that. I usually read around 16-17 at 800rpm, when the car is cold and idling more around 1100rpm, then its like 18-19. I see around 24 on strong engine braking.

 

Yes, I think the errors from idle speed and gauge error are quite large as Nathan pointed out. Altitude also plays a significant role.

I don't think car-to-car comparisons are very useful, given the large amount of deviation you'll see. But, a change in idle vacuum on a particular car can give you an indication of lowered compression (or a vacuum leak, or an idle speed problem, or bad plugs, ...)

-Max