It might be a little difficult to see it but I have a slight fluctuation in the vacuum gauge. I remember my old truck had this but a little worse and I had to replace the valve.

The counter weight in the AFM bounces too. Do I need to be concerned? 

 

 

https://youtu.be/woHqz7JVLQ0

Edited March 17, 201511 yr by rcb280z

Here's another video

https://youtu.be/woHqz7JVLQ0

 

Oops same video. Will get right one loaded soon.

Edited March 17, 201511 yr by rcb280z

Here we go.

https://youtu.be/J9ZxMdVgP9k

BTW, its my 77 280. The one that is in the "Got bored so...." thread. 

 

Im probably sweating over nothing but I don't recall seeing this a couple months ago. I just wonder if there is any correlation between this and the lower compression I got in a couple cylinders when I did a compression test about 6 months ago. A couple of the cylinders were down about 20 psi IIRC. 

If you're concerned about it I would do another compression test.  Remember you looking for the results to stay about 10% of each other, not 10 psi.  If you find 1 cylinder with lower compression you could then do a leak down test to zero in on an exhaust or inlet valve, or a bad gasket leaking into the cooling system, or a bad piston ring.  I've also read about 2 cylinders next to each other with low compression due to a gasket leak between the cylinders.

The good thing is the 2 lower cylinders are not adjacent ones.

I was able to verify exhaust valve problem with the old fashioned way with a piece of paper at the tail pipe. The paper does want to suck into the exhaust. 

Will perform another compression test soon. Have never done a leak down test but am looking forward to doing one.

So are the "leak down" test's easy to perform? I have never done one.

You need a leak down tester tool, you might be able to rent one from orielly or autozone.  The gist is you use compressed air to fill up a cylinder with this gauge attached and it tells you how quickly it leaks out.  Its not hard to do but its not a tool most people have lying around.  I googled this guide for you:

 

http://www.hotrod.com/how-to/engine/116-0406-cylinder-leakdown-tester/

I just looked at a leak down tester at Harbor freight. Might pick up one.

 

Edited March 17, 201511 yr by rcb280z

You need a leak down tester tool, you might be able to rent one from orielly or autozone.  The gist is you use compressed air to fill up a cylinder with this gauge attached and it tells you how quickly it leaks out.  Its not hard to do but its not a tool most people have lying around.  I googled this guide for you:

 

http://www.hotrod.com/how-to/engine/116-0406-cylinder-leakdown-tester/

 

This was really good reading! Thanks for the link.