I need to do a compression test on my car. I need to know the pressure that the guage is supposed to read. I looked in my haynes manual but it doesnt say.

 

Well it should be around 130 - 160 psi depending on mileage and what not. And you shouldn't get a huge gap between each Cyl. So if one is at 150 psi, and the other is 120psi, you've found a problem.

 

Here's some quick thoughts on compression tests...

Less than 5% variation between cylinders = good...

Squirt a bit of oil inside the cylinder being tested, run the test.. if the compression goes up dramatically, you've got o-ring problems...

Compression varies with engine type, heads, ci, combustion chamber size etc...

 

The actual reading isn't nearly as important as the variance. Just make sure that all readings are similar.