Vacuum Test 20inHG and reved 22inHG (good ?)

[mlunsford]

At idle my 4.0L has 20 HG/in and when I rev it the vaccuum drops for a second then the vacuum goes up to about 22HG/in. Does this sound about right ?

I am trying to make sure my cats are not creating back-pressure.

 

[gotmudd]

not sure about a 4.0 but if it was a V8, i'd say it's healthy enough.

 

[Earl43P]

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

http://www.fordf150.net/howto/diagnoseengine.php

 

[MAKG]

That's a golden result.

Very nice.

As long as the needle doesn't have a jitter or periodic low.

It's definitely not a restricted exhaust.

 

[mlunsford]

Thanks,
Nice link too. I would recommend that link be put on the tech page!!

 

[Bird]

Most of the time, a quick jab of the throttle from idle won't show a thing if your cats are clogged unless they're TOTALLY clogged - a steady 1/3+ throttle will actually show you more clearly if they're clogged or another restriction exists in your exhaust system by a slowly dropping vacuum reading.

Bird