Compression Issues

[SSplaytoy]

So as I was testing the problems on the truck, I drove it down the street with the lack of power problem being way worse now and heard a few backfires, but they werent that loud. So out of curiosity I ran another compression test after pulling a few plugs to check to see how it was running. They are white as always, so I do another compression test and find that half the cylinders on both banks have low compression. The gauge bounces up and down between 65 and 75 and when you cut the engine off the gauge holds steady at about 84. I am guessing this would probably mean valves right? I did pull the valve covers again and oil is coming up, rods look fine, and so do the springs. Doubt it is the lifters too. And just an assumption, if I was losing compression due to rings, I would have a steady low compression reading correct?

 

Thanks for any insight

[desrtrat]

try doing a wet compression test to check your rings. if you are getting some back fire, it's possible you burnt some valves. i know that not what you would like to hear.

 

good lick

 

 

edit.. have you run a vacume gauge hooked to intake at idle?

Edited October 13, 2009 by desrtrat (see edit history)

[Punisher]

try doing a wet compression test to check your rings. if you are getting some back fire, it's possible you burnt some valves. i know that not what you would like to hear.

 

good lick

 

 

Squirt some oil in your cylinders that you are doing the test on. Wet compression tests are the most accurate.

Edited October 13, 2009 by Punisher (see edit history)

[SSplaytoy]

I would rather it be the valves than the rings. Swapping heads is a lot easier than pulling the motor out and rebuilding it.

 

I haven't had time to do the leakdown test either, nor have I hooked up a vacuum gauge on the intake. Since I have a lower engine noise I was actually thinking it was blow-by I was hearing down in the crankcase. I just wondered what it meant when the compression jumped up and down.