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weird vacuum at idle

4127 Views 7 Replies 3 Participants Last post by  ic2drop
just asked this in the sr20det section, but i've only had one view so far in a couple of days.. so i thought i'd post it here. if someone wants to delete the other one, or this one, feel free to. i just would like some advice:

Hey, i have a redtop sr20 in my 92 240.. and i'm having a weird vacuum problem at idle. sometimes it idles with 10 mm/hg and sometimes it is 15 mm/hg. i know it should be around 20 mm/hg, and i'm really not sure why it fluctuates sometimes. if i rev it above 1k rpms, the vacuum starts to go more towards 20 mm/hg, so i'm really not sure what this could mean. i've checked the timing, and it seems good... the next thing on my list is to build a boost leak tester, but i was just wondering if anyone else had any ideas on what this could be.

i can hit 7psi easily by the way, just to let whoever know, in case that would help

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If you rev, it shouldn't make more vacuum, it should start moving towards the boost side of the gauge. Also, 200 mm/hg does not seem to be enough. Mine sits near 500 at idle. Are you sure you tapped in to read at the right location? You could also possibly have a vacuum leak.
sorry, i meant to say 20 in. hg.. i have an autometer boost gauge and that is what form the vacuum part is in... its tapped into right spot, i just gave you the wrong units of measure..

and when i said i rev it up, i mean if i give it a little bit of throttle, then it'll go to 20 in. hg when i'm at like 1300 rpms.. but anywhere below 1000 rpms it is at 10 in. hg...
if i step on it to get it into boost, it'll spool up just fine..

i thought it might be a vacuum leak, but it sounds too weird to me.. could i really be losing 10 in. hg by idling? i honestly dont get it.
That's what I was saying, if you add RPM, the vacuum should go down and move more to the positive side. You shouldn't drop to 20 at 1300rpm, it should be opposite. It should sit at 20ish at idle and then go to 10, then past zero and around to the boost pressure side.
so whats wrong here
Not sure, either we are getting mixed up between us, the gauge is bad, or it's hooked up in the wrong spot or there's leak somewhere or I'm picturing the gauge wrong. :scratch:
i'll upload a video tomorrow to show you what i mean
multi threads for the same reason are wrong.
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