I just got my FD back from the paint shop last nite. Now before I left it there 4 weeks ago it was running perfect. I noticed this morning that it is idealing at only 12lbs. of vacuume now.... Any ideas?

 

12lbs of vacum?!?!

 

At ideal the engine used to sit around 16lbs. of vacuume.. now the needle is between 10 and 12. When i gently press the throttle. it goes back to 16 or so. Didn't know if sitting for 3 weeks hurt it or if the shop had been playing with it and damaged the engine.

 

I think he was confused with your unit of measure. Only positive pressure is measured in psi.

 

exactly. thats why im a little confused on what you mean. if you were pulling 12lbs while idling the you'd have to be idling at about 7000 rpm.

vacum is usually measured in either inHg or mmHg. a good running motor will make between 17 and 19 inHg or 420-480 mmHg.

 

oh. gotcha .. well then i'm only pulling @ 12 inhg at ideal. My bad... so you know what i mean now?

 

That really is pretty low. Mine is normally between 19 and 21 which is pretty high.

 

think a line could be loose.. if so where should i look first?

 

I am assuming the 3rd gen vacuum and 2nd gen vacuum are some what related...that said.

Even the smallest leak in the vacuum system could cause it to go up to that. my 2nd gen sits at 13 at idle and goes to 20->21 when I press and let go of the throttle, that says that IDEALLY I should be at 20-21, however there is a small leak that is making it show only 13, that is caused by 3 hoses that I have located and will replace soon.

I wouldn't worry about it too too much, but it would be good to inspect some of those vacuum lines. (its bad on a 2nd gen, probably 10x worse on a 3rd).

Good Luck!

 

What rpm is it idleing at ? 850rpm? Is this with any electrical load on? Fans?

 

it was idleing around 650-700 with no load.

 

Drove it to dinner last nite and it did the same thing on the way over but was fine when i left. Still going ok today also..... I have no idea, it has a mind of it's own.

 

at idle (clutch in rolling) i'm at about 650

at a stand still at idle i'm at 450

are these good levels?

 

My assumption would be that they screwed up your motor if it was just fine before.

650 is a low idle but is ok, I think the ideal idle is at 750-800. Take it to a rotary specialist and have them check it out but first check all the vacuum lines you can.

 

A good solid vacuum at idle *with no load* ie, lights on or AC on, is or should be 15-18. Ported motors have less 12-15 depending on the degree of the port job. My car unported draws 17inHg when at no load idle of 750rpms - the no load factory idle spec IIRC is 720rpms. Lower idel = lowe vacuum, higher idle = more vacuum. Just my thoughts.
Crispy

 

these are vacuum readings not Idles...forgot to mention that

 

Nope! See my post above. Idle this low *will*
result in a vacuum reading of less than normal.
Crispy
Crispy

 

are you guys positive????

I was told that Ideal Vacuum was @ 12hg,
or what ever..

So what does low vacuum signify??
a lose hose or a sign of something more
severe?

 

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

 

OK let me make sure i understand..

My car isn't ported at all. Just bolts ons

CB, DP SMIC, INtake..

and the Vacuum I have on my boost gauge
at idle is 12HG , or what ever...

So Should I BE WORRIEDD???

Dave, Ryan if you two are reading this..
Could a Pill or check valve be on backwards
somewhere or what ever????

 

I left my car at a body shop for about 2 weeks one time and when I got it back I could barely get it started. It had extremely low vacume and if I had too much electrical load and hit the brakes coming to a stop, it would stall out. After a couple days of driving, and a couple of hard runs the car went back to normal. My battery was in good shape, so I believe that the system just needed a good flush after sitting for a couple weeks. So try driving it hard a couple times, go to redline, drive some more and see if it clears it up.

I've noticed that my vacume and idle greatly depend on the amount of fuel I give it at idle. If I lean my idle down with my haltech, my agressive street ported motor will read vacume between 14-15, and idle around 820-880. If I leave the fuel at idle on the normal rich side, it will vacume around 12-13, and idle around 760-820. Of course any kind of electrical load really bogs the car down for some reason, which is probably normal.