1984 Camaro Z28 Leakdown Test - Pressure Points

After connecting the air source, we turned the unlocked regulator knob clockwise until the needle on the right-hand "Cylinder Leakage" gauge was positioned in the middle of the area marked "Set." We pushed the regulator knob down to lock it into place.

With the leakdown tester ready and waiting, we ran the engine until it was good and warm. Then we removed our Z28's air cleaner, oil filler cap, dipstick, radiator cap, and all eight spark plugs. The last two are tough when working with a hot engine, but unlike a compression test, it's critical that the engine be warm for a leakdown test to be accurate. We hand-tightened the adapter hose into the cylinder to be tested, which is quite a feat on a third-gen Camaro with headers-this is one of the few cylinders we could actually see to photograph.

Once the adapter hose was in place in cylinder No. 1, our starting point, we rotated the engine until this cylinder was at top dead center (TDC) on the compression stroke. In our experience, most accurate results were achieved by rotating the engine to this point by hand rather than bumping it with the starter. We've also heard of removing the rocker arms to ensure that both the intake and exhaust valves are closed. Once TDC was acquired, we inserted the free end of the adapter hose into the quick coupler on the test unit

The tester told the tale for this cylinder: 45 percent leakdown, which the Proform unit classifies as moderate. It wasn't as good as we hoped for, or as bad as we feared, but while testing this cylinder, we could actually hear the air escaping through the crankcase breather tube, which meant it was getting past the rings. Given that this engine has new heads but its original lower end, it makes sense.

For the most part, our test subjects came in somewhere between 30 and 45 percent leakdown. It's not great but it is mostly consistent from cylinder to cylinder, which is what you want to see. Cylinder 7, on the other hand, registered a very low 20 percent

For comparison's sake, we also ran a standard cold-cranking compression test on our 305, registering 140-150 psi on all but cylinder 7, which came in at only 130 psi. Well within 10 percent of the other cylinders, it's not a bad number. We mention it to highlight the fact that the two measure different things-this cylinder doesn't create as much pressure as the others, but it also leaks less than the others. Both pieces of info are valuable in determining an engine's condition