What is the compression on a 01 Mazda Tribute 3.0 L.

It should be between 120 psi, and 150 psi , but shouldn't vary more than 10 % between cylinders

According to the ultimate specs.com page, the Mazda Tribute Compression ratio is 10:1. At standard barometric pressure at sea level the atmospheric pressure is 14.9696. The maximum internal cylinder pressure at this barometric pressure would be 149.696 psi but you need to account for the fact that the gage is zeroed at standard atmospheric pressure so 149.696 - 14.9696 = 134.7264 psi. Which would be the theoretical ideal compression for the engine at standard atmospheric pressure as read on a perfectly calibrated compression gage.

Note if your gage is reading in psig (pounds per square inch gage) you need to subtract off the base atmospheric pressure like we did above to get the 134.7264 figure. If your gage is calibrated in psia (pounds per square inch absolute), then you don't do the subtraction and you simply multiply your atmospheric pressure by the compression ratio. So if you your atmospheric pressure is 14.7, then your compression gage in psia should read 147 psia assuming the Mazda 3.0L engine compression ratio of 10:1.

Thus in theory if you know the compression ratio you can do the arithmetic to figure out the rest. To know what the ideal compression at the time and place of measurement, you would need to know the actual atmospheric pressure, which changes with temperature and altitude and weather conditions.

If you have a barometer which reads in in/hg, you can figure out your atmospheric pressure in psi with the formula: 1 in Hg to psi = 0.49115 psi. so if you have a reading of 30 in Hg then 30 * .49115 = 14.7345 psia. So with a store bought barometer and knowledge of your engine compression ratio, you can figure out what your gage ought to be reading in a perfect world.

Now with everything I said, I will tell you that I am working on a 2002 Mazda Tribute ES, and I am getting the following compression readings:

1) 190 2) 185 3) 200 4) 132 5) 155 and 6) 150. So sometimes theory and fact don't always line up and personally I am finding the readings rather puzzling. The worst part of it is that the only thing the Mazda Shop manual says about interpreting the results of the compression test is that it is in spec if all cylinders are within 75% of the highest reading, thanks for that Mazda.