Normal Vacuum?

[scottxd45]

What is the normal vacuum reading supposed to be at idle? Mine is pretty steady at around 15. I was thinking it was supposed to be like 14.7 but I may be thinking of something else.

[FB71]

18-21 inHg

[FestYboy]

i'm pulling 20-23@ 600rpm (depends on temp) out of my B6... and it has head work. i'v also had a stock B3 carby engine idle down to almost 250 w/o stalling and still pulling decent vaccum. so yeah, 15 is LOW, check for leaks...

[WmWatt]

23 on my '89 with 109k km and good compression.
needle should be rock steady, no fluxuation.

[scottxd45]

Cool thanks for the input everybody. I'll try and find/fix my vacuum leak here in the next couple days if I can find some time. There's just not enough hours in a day.

[FB71]

low vacuum does not equal a leak. Other engine issues can cause low vacuum. Incorrect valve or ignition timing, poorly sealing valves or rings, etc.

[miami man]

fb71 is correct

[scottxd45]

low vacuum does not equal a leak. Other engine issues can cause low vacuum. Incorrect valve or ignition timing, poorly sealing valves or rings, etc.

Well I fixed the only vacuum leak I could find, gasket under carb. I think it idles a little smoother but it didn't effect the vacuum reading. My timing light quit working so I can't accuratly set the timing but I did mess with it. If I turned it counterclockwise I could get the vacuum up to a little over 20 at the most but then the idle was too high. I would turn out the idle screw all the way and still it wouldn't come down. Then if I turned it clockwise I could get the idle down where it should be but the vacuum would be low. Very frustrating.

How do you adjust the idle mixture? I just got the manual I bought off ebay in the mail today but it tells you to hook up an exhaust gas analyzer to set it, which of course I don't have.

[jglutz]

Finding a vacuum leak that is external to the engine
Take a propane torch (Benzo-Matic) and turn it on....do not light it.
Run the torch along all of the hoses....connections....and gasket surfaces.
If the idle changes....you located the vacuum leak.

Low vacuum readings and not a tremendous difference in driving....engine power....would most likely be a valve problem.

Also...don't trust your vacuum gage...may be it has a leak or just is not very accurate.

[scottxd45]

Finding a vacuum leak that is external to the engine
Take a propane torch (Benzo-Matic) and turn it on....do not light it.
Run the torch along all of the hoses....connections....and gasket surfaces.
If the idle changes....you located the vacuum leak.

Low vacuum readings and not a tremendous difference in driving....engine power....would most likely be a valve problem.

Also...don't trust your vacuum gage...may be it has a leak or just is not very accurate.

I really don't have any power loss. I don't really have much to compare it with but it's a lot more powerful than I thought a Festiva would be. It doesn't run bad at all except for maybe a finicky idle, it likes to fluctuate sometimes. It's just that I only get about 25 MPG at best. I just got back from driving to indy and back and it didn't even get that good, probly about 20-22. I should have just drove my truck. It get's only about 17 but the improved ride would have been worth it. I hope I can get this figured out before festiva festival!

[WmWatt]

The vaccum diagnosis article at the top of theforum says to check for worn piston rings if vacuum is low. That would be a wet-and-wet compression test. Inexpensive and easy to do at home.

[jglutz]

Scott....I had a recent idle problem that has since been corrected....Thou I'm EFI.

After the engine had warmed up, either by driving or by idle-ing away in the garage, the engine would idle fine/steady at 700RPM, then about every minute or two the idle would drop below 600RPM..putt...putt...putt...for a second or two then kick back up to 700RPM...This was continous situation for over two months before I brought home some elaborate test quipment to figure it out.

I recorded the O2 sensor, crank (CPS) sensor, VAF, and No.1 FI signal. When plotted out, I found that the O2 sensor signal would drift just prior to the RPM hunting. It was a matter of what came first...the chick or the egg. I then disconnected the O2 sensor and generated my own signal; hence, I could make the idel problem come and go on demand. Changed the O2 sensor, no problems since.

[scottxd45]

I think I got this one figured out. I got tired of messing with it so I took it to the dealer. They called me back and said it was running rich and wouldn't idle right because the carb was bad. They said they thought something was warped maybe and they couldn't get another carb so they couldn't do anything. I was a little sceptical at first and thought they were just blowing me off and didn't want to mess with it but I decided to trust their diagnosis. I took the carb off my parts car a brought it to them. The next day they called and said it was done. He installed and adjusted the carb set the timing correctly and corrected a few vacuum lines that were in the wrong spots. It idles perfectly now! Hopefully I will get better gas mileage too! I'll post what I got next time I fill up.