Vacuum a little on the low side? Should I be worried yet?

gottadiesel

Flyin Low
Feb 16, 2009
459
0
0
Vancouver, Washington
As some of you are already aware, I am in the break-in phase of a rebuild. With much help of other members I have been successful in getting past all of my start-up issues so far!

So now I have about 385 miles on it, still running with TruBoost off, so WG spring only and still have not breached 60% throttle. But I did several runs up to 4.5k 2nd - 4th and let engine brake back down during the 1st couple of miles on it, but did not go over Zero (no vacuum no boost)

So my issue when reading the list below by "SupraCentral" is I am hovering in the low zone during idle. At idle 650-700rpms I average 16-18 on my TruBoost readout, I have double checked with gauge at plenum and is close to the same. It does not fluctuate between 16-18 , it might between 16-17 or 17-18 but holds pretty steady.

So is the an issue of break-in period of should I worry about something else being wrong, as some of you may have already seen the testing and such I went through to find issue with missing... also covers this issue also - compression, leak-down, new intake gaskets when I pulled injectors, checked with brake cleaner where I could around intake gaskets but didn't want to get to crazy with the stuff and start a fire :icon_surp...

Any thoughts would be appreciated - Thanks!


* gauge reading steady 17-22 in Hg indicates normal engine in good condition.
* gauge reading low but steady indicates late ignition or valve timing, low compression, stuck throttle valve, leaking manifold gasket, etc..
* gauge reading steady but dropping regularly indicates burnt valve or improper valve clearance.
* gauge reading dropping gradually at idle indicates obstructed exhaust.
* gauge reading slowly dropping to zero as engine speeds up indicates obtructed exhaust.
* gauge reading fluctuating between 15 and 20 in Hg at idle indicates stuck valve or ignition miss.
* gauge reading drifting indicates a minor intake leak at the manifold.
* gauge reading fluctuating as engine speed increases indicates weak valve springs, worn valve stem guides.
* gauge reading vibrating excessively at idle but steady as engine speeds up indicates worn valve guides.
* gauge reading vibrating excessively at all speeds (when not under boost) indicates a blown head gasket.
* healthy decelerating engine reading should jump to 21 thru 27 in Hg as open throttle released.
 

Supracentral

Active Member
Mar 30, 2005
10,542
10
36
Your rings probably haven't seated yet. I wouldn't sweat it. Get 1,000 miles on it and let us know how it's doing then.
 

gottadiesel

Flyin Low
Feb 16, 2009
459
0
0
Vancouver, Washington
Supracentral;1588285 said:
Your rings probably haven't seated yet. I wouldn't sweat it. Get 1,000 miles on it and let us know how it's doing then.

Thank You! That is what I am hoping is going on... I will re-post in about 2 weeks when I am there.. will also have a tuned dyno done in about 2 weeks also...
 

Supracentral

Active Member
Mar 30, 2005
10,542
10
36
montego6500;1588379 said:
not to jack it but i got like 4000 miles on my rebuild and i have hks evc 6 and on that read out vac is only like -11 lbs ov vac is that to low or is it ok

-11 pound/square inch = -22.396 in/hg

That's as good as it gets in a 4 stroke internal combustion engine...
 

gottadiesel

Flyin Low
Feb 16, 2009
459
0
0
Vancouver, Washington
Well after some struggles with some other issues, I have about 2,500 miles on the rebuild... but my vacuum is still at 18-19, I know this is within range, but considering my results for leak-down and compression that I did awhile back, I would think I would be in the 21 range... not sure that I should worry too much, still trying to get a group together to get on a dyno, so far just still working on a street tune.