I posted awhile back about needing help with a harbor freight leak down tester , here's what i found , on several forums people were having the same problem with this tester (US General item # 94190 ) . By the instructions : before you hook up the tester you turn the regulator on the tester all the way down, hook it to your compressor with over a 100 psi from the compressor going to the tester, now screw the hose with the spark plug fitting into the spark plug hole and connect it to the tester . at this point everything is hooked up inline ready to go , now all you need to do ( per the instructions ) is turn the regulator on the tester until the leak down percentage gauge ( right gauge in picture 1 ) is at 0% , now you can read the percentage loss .
This is totally wrong ! when you put the percentage gauge at 0% the psi gauge is only at 15psi. not nearly enough to do a leak down test.What iv read and come up with by messing around with this is that the percentage gauge on this tester is set it be 0% or no leakage at all , with only 15 psi , once you go past 15 psi the percentage gauge will start to wrap around which the instructions say not to do because it will damage the gauge . NOTE : Wikapedia says that you can do a leak down test with 15 psi . this is bull .
what i did at this point was somthing i read about this gauge , it said that the instructions were wrong "per the tech support" You need to turn the regulator on the tester all the way down ( counter clockwise ) then hook it to you compressor which has over 100psi in it , now you turn the regulator on the tester ( clock wise ) until the psi on the tester is at 100psi ( at this point the tester is connected to the compressor but not the spark plug adaptor ) your leakage gauge is not built for this amount of pressure and will wrap aroung and probably be damaged but you dont need it to do this test , it only calculates the numbers from the pressure gauge into a percentage for those who cant do math , next you put the line into the spark plug hole . now with your regulator on the tester set to 100 psi and the piston set to TDC , you hook the tester to the spark plug adaptor , your pressure gauge will drop at this point to what ever the cylinder will hold , this is a constant flow of air so you compressor may try to kick on after awhile. if your tester gauge is regulated to 100psi and you hook it to the cylinder hose and it drops to 95 and stays there then your loss is 5%. in the second and third pics you will see that i put a psi gauge inplace of the leakage gauge on the right now there are two psi gauges there numbers are off from each other by about 5% because they are both shitty gauges. in hind sight i would have just put black tape over the leakage gauge to cover it up as it is usless when testing at 100psi.
Now to my problem : I pulled the engine months ago to put turbos on as my z was smokin its ass off and drinkn oil . my dumb ass put rebuilt turbos on and my car is still smokn its ass off and using oil . the tubros are under warranty and are going back but i was worried that i had a cylinder problem due to all the smoke comming out both sides of the exhaust. I did a compression test and a leak down test and everything seems ok ...tell me what you think of these numbers below . NOTE; My plenum has oil all over the bottom and a puddle in the back of both sides , i did replace the pcv valves , but damn !
compression in all cylinders was between 140 and 145 leakage in all cylinders was between 5% and 7% my newly rebuilt turbos are leaking / dripping oil between the cartridge and the hot side. i dont know if i just have shitty luck and have bad turbos again or if i have another problem..... hows all that oil getting into the plenum ?? the pcv valves ???
here's a pic of a new US General leakage tester
now a pic with the leakage gauge removed and another psi gauge installed in it place . notice the gauge on the left is regulated to 100psi and the connection at the top of the pic is disconnected from the #6 cylinder. 
now a pic with the cylinder connected , notice now that the gauge has dropped to but maintains a steady 95 psi. if you disconnected the cylinder quick connect at this point the pressure should jump right back up to 100 psi on the gauge. 
the gauges are off about 5% from each other in the pics because thay are not correctly calibrated to each other but it doesnt matter you only need to look at one or the other . infact the gauge on the right can be discarded and the port blocked off.
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Harbor freight leak down tester results....here we go.. - 
