Miasma

Hey all,
I just tested my vacuum, and i am getting about 14.5-15inHg. I am wondering if this is ok since I am in Boulder CO. The stuff i have read says that every 1000ft above sea level should drop 1inHg. So at sea level I should have 19.5-20inHg vacuum. Is this right? This is a pretty good reading for a car that turns 8 on march 18th right?

edit: oh, and when i open the throttle, it drops real low, maybe 0, and goes to 20 or so before returning to 15. I am a bit concerned with piston ring leakage though, can anyone comment?

240sxxx

i want to do my vacum test too , but i can't find the place to plug it in . is it on the monifold ?

thanks.

Miasma

i tested from the PCV valve and another random hose connecting to the throttle body.

btw, after 'pinging' the throttle, it only rises up to 17-18inHg, not 20.

i will do a compression test this weekend.

MacGyver265

I think the 1" per 1000 ft is for atmospheric pressure, not engine vacuum. I'm pretty sure the pressure differential should be the same regardless of altitude. I'm not positive on this, but it makes sense to me given the volumetric efficiency of an N/A engine.

iansw

iTrader: (7)

Mine's always read 15hg at idle, 12 in D, and jumps to 18 or 19 when blipping.

But my compression is perfect - mechanics tell me sometimes that's just the way it is....I spent 6 months looking for leaks in the SC System/manifold (removed and changed every gasket on the manifold twice).

I just gave up - it seems to run fine anyway. But I'm at sea level.

Dave B

That's a good point. Does altitude affect the vacuum of an engine? I wouldn't think so because you'd think the Chilton's/Hayne's service manuals would mention something about it.

My vacuum is a steady 20 when the engine is warmed up (1100' above sea level). When I crack the throttle, the vacuum drops like an anvil, and when the throttle is released, the vacuum shoots up to around 25 for a split second before coming back down to a steady 20.

A steady 16-22 is normal. If it's steady, but below 16, you've got a vacuum leak somewhere. If the vacuum jumps back and forth (not steady at all), you could have sticking valves or worn out rings.

I plug my vacuum gauge (MityVac) into the fuel regulator vacuum line located on the fuel rail.


Dave

Miasma

no, i am TELLING you guys that the manual for the vacuum meter AND all the online sites I have seen say that the actual vacuum reading will drop about 1inHg for every 1000ft. i wanted someone to confirm their vacuum at altitude. i will test compression this weekend though, i do not exhibit any signs of leaks and the vacuum gauge response was attributable with a good seal, in that it did not drop slowly and shoot sky high whin bliping the throttle like a leaky seal would. i would be concerned if people above 3000ft (where the logarithmic part of the atmospheric pressure takes over) are getting higher than 19-20inHg. and also, if anyone knew for certain, not speculation, that my reading is ok.