Vacuum reading
 

Hey I jus installed a vacuum gauge on my car and was wondering what all us Non-turbo guys are pullin on the average! I'm between 15 and 16.5 at idle and when I let out throttle in gear about 23-24?

Even for turbo guys we get the same thing.... Sounds bang on to mine

yep - mine too (also turbo).

How much could pre-mix or a de-carbon cleaning change those numbers?

My 07 8 gt auto idles smooth at about 750 rpm, 4 or 5 maf, and 16 constant vacuum at 2900ft elevation.

Unless you have some sort of seal failure I dont think it should change:icon5:

I am usually closer to 18 warmed up for me. 21-22 cold (higher idle) . Same with or without the supercharger. 24ish in gear off throttle.

true dat

So if you live near Fairfield, Ca., you could be under 100ft elevation which would account for your good 18 inches of vaccum.

You generally lose 1 inch for every increase of 1000 ft of elevation assuming same temp, etc.

So mine should read 18 to 19 inches in Fairfield, Ca. ;)

So I don't know much about these things....what's the simplest way to test the idle vacuum reading? (Aside from paying mazda $100 to do it...) Assuming you hook up some tool to the accessory/vaccum nipple thing?
I know my compression numbers are borderline, and that mazda now uses vacuum readings as a measure of engine health, so i'm very curious....

I see -9 PSI cold and a little over -7 PSI hot.
That translates roughly to 18" & 14", respectively.

I am at 1300 feet.

Thanks for that tip Charles!

How much does a vacuum reading equate to determining low compression?

There is a correlation, but it is kinda fuzzy as the range of vacuum readings for both a "good" and "bad" motor overlap quite a bit.
In my experience, a warm 90 PSI motor will make about the same vacuum as a warm 115 PSI motor.

Accessory load can decrease vacuum. Make sure you turn everything off.

Okay, so I tested mine. I have about 26,000 on my Mazda reman. This picture is what I was seeing hot at idle.

http://www.flickr.com/photos/9krpmrx8/5565947762/

I was a little worried at the somewhat low reading for such a low mileage engine. But then I tested Hoss-05's car (05' M/T 10k on reman) and sillwhitegirls car (07' M/T 43k original engine) and basically their readings were the same.

Thoughts? I did a zoom zoom cleaning right now and I will test after I get back from a drive.

Okay I tested mine with a different vacuum tester I had and it was still at a tad bit past 15 at hot idle after the zoom zoom cleaning. So both of my vacuum testers seem to be inline with each other. I also tested grungepups 07' M/T with 50k on original engine and he was steady at about 14 :(

Hot idle on a healthy motor can be anywhere from 13" to 20", depending on altitude and other things.

Oh ok, I thought factory spec was 17-20. I have a secondary air leak (blip of powerloss) somewhere that only shows at 6,000-7,000RPM. You can see it on the data logs and I am trying to diagnose and I was worried my motor might not be up to snuff. The issue does not happen all the time, but about half the time I take her to redline. But my MAF readings at redline (195 or so) seem lower than others are.

Last time I was in SA, I tested 18 inches vacuum hot at idle on my VW vacuum guage from my 1980 Scirocco.

When, I come over Thursday after your workday, we can test with both guages if you want.

We can even put those new plugs in mine, and see if that improves it some more if you like testing stuff. :eyetwitch

Mine was sitting steady however grungepup had the lowest reading and it was moving a bit back and forth. He has kind of suspected his engine was on the outs but his car runs really strong so who knows.

I will have to look into testing the APV motor, it does have 122,000 on it. On a side note though, I cleaned my ESS after doing the zoom zoom cleaning and the problem has not came up since but we will see after a couple of days of driving if it comes back.

trying to analyze engine sealing outside of gross variations is a waste of time & effort, which makes it the perfect forum topic

Yeah, well hopefully I will have a compression tester soon enough and I can test it that way as well.

Sub, My car seems to be acting the same way...

Replacing my plugs fixed it. I will get some vacuum readings tonight to see if that changed.