How Accurate are Vacuum Gauges?

[savatreatabvr]

Everyone I talked to told me to buy a vacuum gauge to help troubleshoot why my mid 70's 454 acts like it's running on 7 cylinders! I finally broke down and bought a vacuum gauge thinking it was the answer, thinking it was some magical tool that would point me in the right direction! WRONG! I hooked it up to manifold vacuum and long behold, it says everything is pretty much normal! Well I've done everything short of rebuilding the motor so now I'm at a complete loss! So here's the question, how accurate are these vacuum gauges?

[JMac11]

It holds a steady 20 at idle? Goes down as you open the throttle??

[Pyrotechnic]

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

That may help you interpret the readings and needle motion. It's best to have the gauge mounted in the cab where you can see it while driving.

[savatreatabvr]

According to your link, http://www.classictruckshop.com/club...ts/vac/uum.htm, it says my timing is retarded! If anything is retarded it's me, lol because I've been trying to figure this out for over a year! I'm close to concurring this beast so any help on fine tuning my timing would be mucho appreciateo!

Originally Posted by Pyrotechnic

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

That may help you interpret the readings and needle motion. It's best to have the gauge mounted in the cab where you can see it while driving.

[savatreatabvr]

If average vacuum at idle is right around 20Hg, then mine idling right around 16 or 17 means a vacuum leak, right?

[geezer#99]

Your vacuum may be lower due to elevation, timing, mixture screw adjustment, type of camshaft used, compression or cam position.
16 HG doesn't indicate a vacuum leak.

[savatreatabvr]

I QUIT! I gave it my best shot and failed! According to several friends it runs fine, I am kind of a perfectionist so I may have been wanting to much out of it but I've got other projects to attend to so I'm either parking it or selling it!!!

[Redcap]

Originally Posted by savatreatabvr

I QUIT! I gave it my best shot and failed! According to several friends it runs fine, I am kind of a perfectionist so I may have been wanting to much out of it but I've got other projects to attend to so I'm either parking it or selling it!!!

No one likes a quitter.

[INSIDIOUS '86]

Originally Posted by savatreatabvr

I QUIT! I gave it my best shot and failed! According to several friends it runs fine, I am kind of a perfectionist so I may have been wanting to much out of it but I've got other projects to attend to so I'm either parking it or selling it!!!

Put a real cam intake and headers in that 454 260hp is nothing to fart about in a big block so just build a real big block
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[fanmanj]

FIRST.. cool down... relax.. go have a beer or 2 if you drink. Come back to it later... when you do.. loosen the holddown on the distributor slightly, and turn the cap clockwise slightly with the engine idling... watch your vacuum gauge. did it go up? if so keep going till you get around 20" of vacuum... go drive the truck... romp on it hard a few times... does it ping? if so, turn your distrubitor back slightly until you can drive it with the highest vacuum reading, most power, and NO ping. there, you have timed your engine.. try that before you sell it

[86 K-10]

Originally Posted by savatreatabvr

Everyone I talked to told me to buy a vacuum gauge to help troubleshoot why my mid 70's 454 acts like it's running on 7 cylinders! I finally broke down and bought a vacuum gauge thinking it was the answer, thinking it was some magical tool that would point me in the right direction! WRONG! I hooked it up to manifold vacuum and long behold, it says everything is pretty much normal! Well I've done everything short of rebuilding the motor so now I'm at a complete loss! So here's the question, how accurate are these vacuum gauges?

that's because it's a 70's 454. a vacuum gauge is a valuable diagnostic tool, but it can't polish a turd (i'm assuming it's a stock engine)

are you still running all the smog equipment?

[Corts60]

I never a vacuum gauge for anything more than checking my air/fuel mixture screws. I set initial and full advance with a timing light and then lastly set the air/fuel screws with the vacuum gauge. Normal engine vacuum at idle can be anywhere from 16-21 in hg, depending on your set up and all the things geezer mentioned above.
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[savatreatabvr]

As far as I know it's stock except chrome valve covers and air cleaner! No smog equipment, not even an EGR valve! I set the air/fuel mixture and timing and it runs much better but I'm still tuning!

Originally Posted by 86 K-10

that's because it's a 70's 454. a vacuum gauge is a valuable diagnostic tool, but it can't polish a turd (i'm assuming it's a stock engine)

are you still running all the smog equipment?

[savatreatabvr]

I still have questions on the initial and full advance timing? I've set the initial timing but how do I set the advanced timing?