Best Vacuum source?

[lostscotiaguy]

I realize that there's several places I can attach a vacuum gauge, but I was hoping to get people's opinions on the BEST location for a hook-up. I'm planning on using a t-fitting and basically hooking up a gauge permanently (or semi-permanently) mostly just for carb tuning.

[lostforawhile]

I realize that there's several places I can attach a vacuum gauge, but I was hoping to get people's opinions on the BEST location for a hook-up. I'm planning on using a t-fitting and basically hooking up a gauge permanently (or semi-permanently) mostly just for carb tuning.you want manifold vaccume, so anything tied into the manifold just T into it, A vaccume gauge is a great tool to permanently have in the car, it will tell you all kinds of stuff about what the engine is doing, everyone wants an AF gauge, but the lowly vacuum gauge is a huge tuning help and engine monitoring help

[lostforawhile]

here's an excellent link for you all about reading the gauge, you can click on each scenario and it shows the gauge moving and what it means

http://www.secondchancegarage.com/public/186.cfm

[lostscotiaguy]

"everyone wants an AF gauge" LOL Amen to that, If I had a drill press and knew how to weld, I'd put my own O2 Sensor in! It sure would make things easier, as I've never managed to get my friggin carb dialed in properly! Otherwise, thanks for the help!

[Dr_Snooz]

I bought an A/F meter from Edelbrock to get my truck's carb dialed in. It wasn't cheap and I had to pay a muffler shop to weld the O2 sensor threads into place. For all the good it did me, I might as well have shoved the sensor up my butt. It has pretty lights, but is fairly well useless otherwise. I've bought two things from Edelbrock now and both were equally bad so maybe it's just Edelbrock, but I'd still say save your money. I finally got the carb tuned (and passed smog) using my nose and feeling how the truck ran down the road with different jet settings. You have to spend a lot of time learning what all the carb adjustments do, what rich exhaust smells like and what lean misfire feels like. Then just tinker until you get it right.

Anyway, the best vacuum source is the one closest to where you want to run the gauge and the easiest to get to that isn't controlled in some way or other by a smog device.

[lostforawhile]

I bought an A/F meter from Edelbrock to get my truck's carb dialed in. It wasn't cheap and I had to pay a muffler shop to weld the O2 sensor threads into place. For all the good it did me, I might as well have shoved the sensor up my butt. It has pretty lights, but is fairly well useless otherwise. I've bought two things from Edelbrock now and both were equally bad so maybe it's just Edelbrock, but I'd still say save your money. I finally got the carb tuned (and passed smog) using my nose and feeling how the truck ran down the road with different jet settings. You have to spend a lot of time learning what all the carb adjustments do, what rich exhaust smells like and what lean misfire feels like. Then just tinker until you get it right.

Anyway, the best vacuum source is the one closest to where you want to run the gauge and the easiest to get to that isn't controlled in some way or other by a smog device.
those eldebrock gauges are a narrow band gauge, basically the sensor is producing voltage or not, a wideband gauge is much more accurate and is very useful in tuning, the narrow band basically show rich or lean, the wideband gauges will show the actual mixture

[Dr_Snooz]

I'd be happy with rich or lean. It doesn't do either. Unless it does both. Sometimes it's blank and others blinking too rich, or too lean, or just right, under the exact same conditions. Sometimes the lights flash sporadically around a level and other times they are stone solid. Good grief. I still say you can do better by deepening your understanding of how carbs control the mixture under various conditions (jets, metering rods, stepup springs, floats, accelerator pumps, etc.) and learning what lean misfire feels like. Once you have that all figured out, you just lean each control out until it misfires and then back off until it stops. If it stinks like raw fuel, it's too rich. The A/F gauge did help to sort of confirm what my nose told me, but it was so variable in its readings that I ultimately just went with my nose.

[cygnus x-1]

I'd be happy with rich or lean. It doesn't do either. Unless it does both. Sometimes it's blank and others blinking too rich, or too lean, or just right, under the exact same conditions. Sometimes the lights flash sporadically around a level and other times they are stone solid. Good grief. I still say you can do better by deepening your understanding of how carbs control the mixture under various conditions (jets, metering rods, stepup springs, floats, accelerator pumps, etc.) and learning what lean misfire feels like. Once you have that all figured out, you just lean each control out until it misfires and then back off until it stops. If it stinks like raw fuel, it's too rich. The A/F gauge did help to sort of confirm what my nose told me, but it was so variable in its readings that I ultimately just went with my nose.


Narrow band sensors are useless for actually *measuring* AFR. All they tell you is which side of the stoichiometric point you're on, rich or lean. That's fine for the stock computer because all it want's to do is keep the mixture at the stoich point for most driving conditions. Under hard throttle the computer goes open loop (no O2 feedback) and uses preprogrammed values.

If you don't want to shell out the bucks for a wideband O2 then you can learn to read the plugs. That's how it was done before WBO2.


C|

[POS carb]

what happened to the original question?
You can get a solid vacuum signal from the metal "pipe" sticking out of the back of the intake manifold, below the booster hose. they point towards the firewall.

http://memimage.cardomain.com/ride_images/1/3036/2781/7588890059_large.jpg

a side note on the a/f
it is true, regular o2 sensors are more like on/off switches.
a wideband is necessary for accurate tuning.
I was working on a Mustang with an AEM a/f gauge kit that had a burned up sensor. I found out that the 03 Altima has the same exact wideband sensor and can be had a lot cheaper than getting it through AEM

[POS carb]

Anyway, the best vacuum source is the one closest to where you want to run the gauge and the easiest to get to that isn't controlled in some way or other by a smog device.

my bad snooz :flash: