I present comparative engine health testing results on my '99 Corolla... with about 127,000 miles on it. Car was acquired with about 100,000 miles, some 15 or so years ago. Not much use 
.
I tested the car cold, using the FAA directed leakdown testing method (used for piston engined aircraft). My reason for the FAA process is because in the automotive world no standard exists for the orifice used for the leakdown testing equipment. FAA is, by comparison, very specific. Limits of rejection for the FAA test is 25% leakdown.
I also tested the car hot, using the same test rig. Finally, I tested with my compression tester, hot, with throttle on the floor and fuel inj. relay pulled.
See comparative results, attached.
My Dad's '50's or 60's vintage SnapOn compression tester says, on the face of the gauge, that cylinders should be no more than 10 psi different from one another. Others say cylinders should be no more than 10% different from one another (using the classic compression test). Incidentally, I did not use my old SnapOn; it's too old and likely has lost accuracy, leaks, etc. I have a much newer device.
My point in showing the comparison between traditional compression testing and leakdown testing is that they tell different stories, sometimes. With a traditional compression test, not only the final figure is important, but the vigour with which it reaches the final figure. If you get high compression pressures, even on the 2nd "hit", that's vigorous and healthy. If it agonizingly slowly gets to final... that's not so good.
Incidentally, all quick-connect fittings downstream of the restriction orifice, on my (rather ugly) leakdown tester are pressure washer type... low restriction/through-bore. If they were traditional compressed air type couplers they might affect the results.
Discussion on this would be welcomed!
.I tested the car cold, using the FAA directed leakdown testing method (used for piston engined aircraft). My reason for the FAA process is because in the automotive world no standard exists for the orifice used for the leakdown testing equipment. FAA is, by comparison, very specific. Limits of rejection for the FAA test is 25% leakdown.
I also tested the car hot, using the same test rig. Finally, I tested with my compression tester, hot, with throttle on the floor and fuel inj. relay pulled.
See comparative results, attached.
My Dad's '50's or 60's vintage SnapOn compression tester says, on the face of the gauge, that cylinders should be no more than 10 psi different from one another. Others say cylinders should be no more than 10% different from one another (using the classic compression test). Incidentally, I did not use my old SnapOn; it's too old and likely has lost accuracy, leaks, etc. I have a much newer device.
My point in showing the comparison between traditional compression testing and leakdown testing is that they tell different stories, sometimes. With a traditional compression test, not only the final figure is important, but the vigour with which it reaches the final figure. If you get high compression pressures, even on the 2nd "hit", that's vigorous and healthy. If it agonizingly slowly gets to final... that's not so good.
Incidentally, all quick-connect fittings downstream of the restriction orifice, on my (rather ugly) leakdown tester are pressure washer type... low restriction/through-bore. If they were traditional compressed air type couplers they might affect the results.
Discussion on this would be welcomed!
