Well i had a new engine out in about 3 3 months ago and i broke it in and my vacuum was great,it was 18-20 at idle.I broke it in first 500 hundred miles didn't get on the boost,stayed around 2 k rpms,did oil change,drove it alittle harder but still no boost untill 1500.My vacuum was 16-18 at idle and my idle is about 250 -400 rpms. Well i installed the boost gauge when i had the new engine,so when i broke thee engine past 2000 miles i started to get on the boost and my boost pattern was like 5-4-5,So i drove it for a month like and now my vaccum reading at idle is at best 14 and most of the time 12.Which is low.I have the cat off now and only getting 6 to 7 lbs of boost with rebuilt turbos.What could making my vacuum reading so low,should i be concerned,do i newed a better remanufactured motor?

 

If all you are getting is 7 lbs of boost then your hoses might be leaking. This would also cause the vacuum pressure to be down. After I installed my hi flow cat and cat back (downpipe was already on) my vacuum pressure that used to be 20-22 is now at 16-18. I guess the higher flowing exhaust has something to do with it too.

 

Don't the electrical systems also have to do with the vacuum readings? More electrical load = less vacuum?
I know when I had a bad fan relay my vacuum wasn't all that it should be...