crazywhiteboy89

iTrader: (1)

on the boost gague when idealing what sould it idea at -hg what ? and is -17.6 to -18.5 hh good or bad?

Nighthawk243

Normal levels. You don't really need to worry about Vac all that much.

crazywhiteboy89

iTrader: (1)

really that good what would bad be?

Nighthawk243

Say your car is idling and sitting at 5mmHg at idle... that would be considered bad. If it starts wavering back and forth at a steady rpm, thats a sign of trouble. The boost gauge when the engine is held at a particular RPM should stay steady. This is a general guide of what the VAC side of gauge says about the engine:

http://www.classictruckshop.com/club...ts/vac/uum.htm

Since you have a boosted vehicle, your car will show boost. On a naturally aspirated car, the vehicle won't go into boost at all, just get closer to 0mmHG at WOT.

crazywhiteboy89

iTrader: (1)

thanks alot. what does ur car idle at just to know and mine at idle is not really steady it bounch from -17.6 to -18.5hg and sometime goes to -19.1hg brought to the dealer they told me that no vaccume leaks but other on the forum told me it is so idk lol. but is that ok?

slowswap

-15 inHg or less and I'd do a compression test. A healthy motor is around -18 to -20 inHg at idle.

crazywhiteboy89

iTrader: (1)

just had one done couple months ago it was fine. i started driven it again less that 2 months ago and -15 or less is ok ?

slowswap

-16 to -20 is ok. 0 to -15 at idle and it's time for a compression test.

crazywhiteboy89

iTrader: (1)

yea no where near that but i have one done just incase thank

dannysauer

iTrader: (3)

I know this is old but my car idles at -15hg and was wondering if anyone knows what would cause this. I did a compression test and came out good replaced all the vac lines and checked my intake manifold gasket that was ok

mrbelvedere

iTrader: (3)

what was the compression on the cylinders the main things that will cause low vacuum readings is cams out of time and low cylinder pressure vacuum at idle should be 19in

dannysauer

iTrader: (3)

155 155 160 155

mrbelvedere

iTrader: (3)

that is why your manifold vacuum is low your cylinder pressure is really low the the compression should be 180 to 210 time for a rebuild

dannysauer

iTrader: (3)

I figure my compression was ok for being 5280 ft above sea level but I'm going to do a leak down test and go from there thanks for the input

chris88z24

The factory autometer gages aren't that accurate, btw.